Merge branches 'irq/genirq' and 'linus' into irq/core
[pandora-kernel.git] / net / ipv4 / tcp_input.c
1 /*
2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
3  *              operating system.  INET is implemented using the  BSD Socket
4  *              interface as the means of communication with the user level.
5  *
6  *              Implementation of the Transmission Control Protocol(TCP).
7  *
8  * Authors:     Ross Biro
9  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10  *              Mark Evans, <evansmp@uhura.aston.ac.uk>
11  *              Corey Minyard <wf-rch!minyard@relay.EU.net>
12  *              Florian La Roche, <flla@stud.uni-sb.de>
13  *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14  *              Linus Torvalds, <torvalds@cs.helsinki.fi>
15  *              Alan Cox, <gw4pts@gw4pts.ampr.org>
16  *              Matthew Dillon, <dillon@apollo.west.oic.com>
17  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18  *              Jorge Cwik, <jorge@laser.satlink.net>
19  */
20
21 /*
22  * Changes:
23  *              Pedro Roque     :       Fast Retransmit/Recovery.
24  *                                      Two receive queues.
25  *                                      Retransmit queue handled by TCP.
26  *                                      Better retransmit timer handling.
27  *                                      New congestion avoidance.
28  *                                      Header prediction.
29  *                                      Variable renaming.
30  *
31  *              Eric            :       Fast Retransmit.
32  *              Randy Scott     :       MSS option defines.
33  *              Eric Schenk     :       Fixes to slow start algorithm.
34  *              Eric Schenk     :       Yet another double ACK bug.
35  *              Eric Schenk     :       Delayed ACK bug fixes.
36  *              Eric Schenk     :       Floyd style fast retrans war avoidance.
37  *              David S. Miller :       Don't allow zero congestion window.
38  *              Eric Schenk     :       Fix retransmitter so that it sends
39  *                                      next packet on ack of previous packet.
40  *              Andi Kleen      :       Moved open_request checking here
41  *                                      and process RSTs for open_requests.
42  *              Andi Kleen      :       Better prune_queue, and other fixes.
43  *              Andrey Savochkin:       Fix RTT measurements in the presence of
44  *                                      timestamps.
45  *              Andrey Savochkin:       Check sequence numbers correctly when
46  *                                      removing SACKs due to in sequence incoming
47  *                                      data segments.
48  *              Andi Kleen:             Make sure we never ack data there is not
49  *                                      enough room for. Also make this condition
50  *                                      a fatal error if it might still happen.
51  *              Andi Kleen:             Add tcp_measure_rcv_mss to make
52  *                                      connections with MSS<min(MTU,ann. MSS)
53  *                                      work without delayed acks.
54  *              Andi Kleen:             Process packets with PSH set in the
55  *                                      fast path.
56  *              J Hadi Salim:           ECN support
57  *              Andrei Gurtov,
58  *              Pasi Sarolahti,
59  *              Panu Kuhlberg:          Experimental audit of TCP (re)transmission
60  *                                      engine. Lots of bugs are found.
61  *              Pasi Sarolahti:         F-RTO for dealing with spurious RTOs
62  */
63
64 #include <linux/mm.h>
65 #include <linux/module.h>
66 #include <linux/sysctl.h>
67 #include <net/dst.h>
68 #include <net/tcp.h>
69 #include <net/inet_common.h>
70 #include <linux/ipsec.h>
71 #include <asm/unaligned.h>
72 #include <net/netdma.h>
73
74 int sysctl_tcp_timestamps __read_mostly = 1;
75 int sysctl_tcp_window_scaling __read_mostly = 1;
76 int sysctl_tcp_sack __read_mostly = 1;
77 int sysctl_tcp_fack __read_mostly = 1;
78 int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
79 int sysctl_tcp_ecn __read_mostly;
80 int sysctl_tcp_dsack __read_mostly = 1;
81 int sysctl_tcp_app_win __read_mostly = 31;
82 int sysctl_tcp_adv_win_scale __read_mostly = 2;
83
84 int sysctl_tcp_stdurg __read_mostly;
85 int sysctl_tcp_rfc1337 __read_mostly;
86 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
87 int sysctl_tcp_frto __read_mostly = 2;
88 int sysctl_tcp_frto_response __read_mostly;
89 int sysctl_tcp_nometrics_save __read_mostly;
90
91 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
92 int sysctl_tcp_abc __read_mostly;
93
94 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
95 #define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
96 #define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
97 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
98 #define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
99 #define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
100 #define FLAG_ECE                0x40 /* ECE in this ACK                         */
101 #define FLAG_DATA_LOST          0x80 /* SACK detected data lossage.             */
102 #define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
103 #define FLAG_ONLY_ORIG_SACKED   0x200 /* SACKs only non-rexmit sent before RTO */
104 #define FLAG_SND_UNA_ADVANCED   0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
105 #define FLAG_DSACKING_ACK       0x800 /* SACK blocks contained D-SACK info */
106 #define FLAG_NONHEAD_RETRANS_ACKED      0x1000 /* Non-head rexmitted data was ACKed */
107 #define FLAG_SACK_RENEGING      0x2000 /* snd_una advanced to a sacked seq */
108
109 #define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
110 #define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
111 #define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
112 #define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
113 #define FLAG_ANY_PROGRESS       (FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
114
115 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
116 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
117
118 /* Adapt the MSS value used to make delayed ack decision to the
119  * real world.
120  */
121 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
122 {
123         struct inet_connection_sock *icsk = inet_csk(sk);
124         const unsigned int lss = icsk->icsk_ack.last_seg_size;
125         unsigned int len;
126
127         icsk->icsk_ack.last_seg_size = 0;
128
129         /* skb->len may jitter because of SACKs, even if peer
130          * sends good full-sized frames.
131          */
132         len = skb_shinfo(skb)->gso_size ? : skb->len;
133         if (len >= icsk->icsk_ack.rcv_mss) {
134                 icsk->icsk_ack.rcv_mss = len;
135         } else {
136                 /* Otherwise, we make more careful check taking into account,
137                  * that SACKs block is variable.
138                  *
139                  * "len" is invariant segment length, including TCP header.
140                  */
141                 len += skb->data - skb_transport_header(skb);
142                 if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
143                     /* If PSH is not set, packet should be
144                      * full sized, provided peer TCP is not badly broken.
145                      * This observation (if it is correct 8)) allows
146                      * to handle super-low mtu links fairly.
147                      */
148                     (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
149                      !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
150                         /* Subtract also invariant (if peer is RFC compliant),
151                          * tcp header plus fixed timestamp option length.
152                          * Resulting "len" is MSS free of SACK jitter.
153                          */
154                         len -= tcp_sk(sk)->tcp_header_len;
155                         icsk->icsk_ack.last_seg_size = len;
156                         if (len == lss) {
157                                 icsk->icsk_ack.rcv_mss = len;
158                                 return;
159                         }
160                 }
161                 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
162                         icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
163                 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
164         }
165 }
166
167 static void tcp_incr_quickack(struct sock *sk)
168 {
169         struct inet_connection_sock *icsk = inet_csk(sk);
170         unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
171
172         if (quickacks == 0)
173                 quickacks = 2;
174         if (quickacks > icsk->icsk_ack.quick)
175                 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
176 }
177
178 void tcp_enter_quickack_mode(struct sock *sk)
179 {
180         struct inet_connection_sock *icsk = inet_csk(sk);
181         tcp_incr_quickack(sk);
182         icsk->icsk_ack.pingpong = 0;
183         icsk->icsk_ack.ato = TCP_ATO_MIN;
184 }
185
186 /* Send ACKs quickly, if "quick" count is not exhausted
187  * and the session is not interactive.
188  */
189
190 static inline int tcp_in_quickack_mode(const struct sock *sk)
191 {
192         const struct inet_connection_sock *icsk = inet_csk(sk);
193         return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
194 }
195
196 static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp)
197 {
198         if (tp->ecn_flags & TCP_ECN_OK)
199                 tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
200 }
201
202 static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, struct sk_buff *skb)
203 {
204         if (tcp_hdr(skb)->cwr)
205                 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
206 }
207
208 static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp)
209 {
210         tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
211 }
212
213 static inline void TCP_ECN_check_ce(struct tcp_sock *tp, struct sk_buff *skb)
214 {
215         if (tp->ecn_flags & TCP_ECN_OK) {
216                 if (INET_ECN_is_ce(TCP_SKB_CB(skb)->flags))
217                         tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
218                 /* Funny extension: if ECT is not set on a segment,
219                  * it is surely retransmit. It is not in ECN RFC,
220                  * but Linux follows this rule. */
221                 else if (INET_ECN_is_not_ect((TCP_SKB_CB(skb)->flags)))
222                         tcp_enter_quickack_mode((struct sock *)tp);
223         }
224 }
225
226 static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, struct tcphdr *th)
227 {
228         if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
229                 tp->ecn_flags &= ~TCP_ECN_OK;
230 }
231
232 static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, struct tcphdr *th)
233 {
234         if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
235                 tp->ecn_flags &= ~TCP_ECN_OK;
236 }
237
238 static inline int TCP_ECN_rcv_ecn_echo(struct tcp_sock *tp, struct tcphdr *th)
239 {
240         if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
241                 return 1;
242         return 0;
243 }
244
245 /* Buffer size and advertised window tuning.
246  *
247  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
248  */
249
250 static void tcp_fixup_sndbuf(struct sock *sk)
251 {
252         int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
253                      sizeof(struct sk_buff);
254
255         if (sk->sk_sndbuf < 3 * sndmem)
256                 sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
257 }
258
259 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
260  *
261  * All tcp_full_space() is split to two parts: "network" buffer, allocated
262  * forward and advertised in receiver window (tp->rcv_wnd) and
263  * "application buffer", required to isolate scheduling/application
264  * latencies from network.
265  * window_clamp is maximal advertised window. It can be less than
266  * tcp_full_space(), in this case tcp_full_space() - window_clamp
267  * is reserved for "application" buffer. The less window_clamp is
268  * the smoother our behaviour from viewpoint of network, but the lower
269  * throughput and the higher sensitivity of the connection to losses. 8)
270  *
271  * rcv_ssthresh is more strict window_clamp used at "slow start"
272  * phase to predict further behaviour of this connection.
273  * It is used for two goals:
274  * - to enforce header prediction at sender, even when application
275  *   requires some significant "application buffer". It is check #1.
276  * - to prevent pruning of receive queue because of misprediction
277  *   of receiver window. Check #2.
278  *
279  * The scheme does not work when sender sends good segments opening
280  * window and then starts to feed us spaghetti. But it should work
281  * in common situations. Otherwise, we have to rely on queue collapsing.
282  */
283
284 /* Slow part of check#2. */
285 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
286 {
287         struct tcp_sock *tp = tcp_sk(sk);
288         /* Optimize this! */
289         int truesize = tcp_win_from_space(skb->truesize) >> 1;
290         int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
291
292         while (tp->rcv_ssthresh <= window) {
293                 if (truesize <= skb->len)
294                         return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
295
296                 truesize >>= 1;
297                 window >>= 1;
298         }
299         return 0;
300 }
301
302 static void tcp_grow_window(struct sock *sk, struct sk_buff *skb)
303 {
304         struct tcp_sock *tp = tcp_sk(sk);
305
306         /* Check #1 */
307         if (tp->rcv_ssthresh < tp->window_clamp &&
308             (int)tp->rcv_ssthresh < tcp_space(sk) &&
309             !tcp_memory_pressure) {
310                 int incr;
311
312                 /* Check #2. Increase window, if skb with such overhead
313                  * will fit to rcvbuf in future.
314                  */
315                 if (tcp_win_from_space(skb->truesize) <= skb->len)
316                         incr = 2 * tp->advmss;
317                 else
318                         incr = __tcp_grow_window(sk, skb);
319
320                 if (incr) {
321                         tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
322                                                tp->window_clamp);
323                         inet_csk(sk)->icsk_ack.quick |= 1;
324                 }
325         }
326 }
327
328 /* 3. Tuning rcvbuf, when connection enters established state. */
329
330 static void tcp_fixup_rcvbuf(struct sock *sk)
331 {
332         struct tcp_sock *tp = tcp_sk(sk);
333         int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
334
335         /* Try to select rcvbuf so that 4 mss-sized segments
336          * will fit to window and corresponding skbs will fit to our rcvbuf.
337          * (was 3; 4 is minimum to allow fast retransmit to work.)
338          */
339         while (tcp_win_from_space(rcvmem) < tp->advmss)
340                 rcvmem += 128;
341         if (sk->sk_rcvbuf < 4 * rcvmem)
342                 sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
343 }
344
345 /* 4. Try to fixup all. It is made immediately after connection enters
346  *    established state.
347  */
348 static void tcp_init_buffer_space(struct sock *sk)
349 {
350         struct tcp_sock *tp = tcp_sk(sk);
351         int maxwin;
352
353         if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
354                 tcp_fixup_rcvbuf(sk);
355         if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
356                 tcp_fixup_sndbuf(sk);
357
358         tp->rcvq_space.space = tp->rcv_wnd;
359
360         maxwin = tcp_full_space(sk);
361
362         if (tp->window_clamp >= maxwin) {
363                 tp->window_clamp = maxwin;
364
365                 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
366                         tp->window_clamp = max(maxwin -
367                                                (maxwin >> sysctl_tcp_app_win),
368                                                4 * tp->advmss);
369         }
370
371         /* Force reservation of one segment. */
372         if (sysctl_tcp_app_win &&
373             tp->window_clamp > 2 * tp->advmss &&
374             tp->window_clamp + tp->advmss > maxwin)
375                 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
376
377         tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
378         tp->snd_cwnd_stamp = tcp_time_stamp;
379 }
380
381 /* 5. Recalculate window clamp after socket hit its memory bounds. */
382 static void tcp_clamp_window(struct sock *sk)
383 {
384         struct tcp_sock *tp = tcp_sk(sk);
385         struct inet_connection_sock *icsk = inet_csk(sk);
386
387         icsk->icsk_ack.quick = 0;
388
389         if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
390             !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
391             !tcp_memory_pressure &&
392             atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
393                 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
394                                     sysctl_tcp_rmem[2]);
395         }
396         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
397                 tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
398 }
399
400 /* Initialize RCV_MSS value.
401  * RCV_MSS is an our guess about MSS used by the peer.
402  * We haven't any direct information about the MSS.
403  * It's better to underestimate the RCV_MSS rather than overestimate.
404  * Overestimations make us ACKing less frequently than needed.
405  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
406  */
407 void tcp_initialize_rcv_mss(struct sock *sk)
408 {
409         struct tcp_sock *tp = tcp_sk(sk);
410         unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
411
412         hint = min(hint, tp->rcv_wnd / 2);
413         hint = min(hint, TCP_MIN_RCVMSS);
414         hint = max(hint, TCP_MIN_MSS);
415
416         inet_csk(sk)->icsk_ack.rcv_mss = hint;
417 }
418
419 /* Receiver "autotuning" code.
420  *
421  * The algorithm for RTT estimation w/o timestamps is based on
422  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
423  * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
424  *
425  * More detail on this code can be found at
426  * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
427  * though this reference is out of date.  A new paper
428  * is pending.
429  */
430 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
431 {
432         u32 new_sample = tp->rcv_rtt_est.rtt;
433         long m = sample;
434
435         if (m == 0)
436                 m = 1;
437
438         if (new_sample != 0) {
439                 /* If we sample in larger samples in the non-timestamp
440                  * case, we could grossly overestimate the RTT especially
441                  * with chatty applications or bulk transfer apps which
442                  * are stalled on filesystem I/O.
443                  *
444                  * Also, since we are only going for a minimum in the
445                  * non-timestamp case, we do not smooth things out
446                  * else with timestamps disabled convergence takes too
447                  * long.
448                  */
449                 if (!win_dep) {
450                         m -= (new_sample >> 3);
451                         new_sample += m;
452                 } else if (m < new_sample)
453                         new_sample = m << 3;
454         } else {
455                 /* No previous measure. */
456                 new_sample = m << 3;
457         }
458
459         if (tp->rcv_rtt_est.rtt != new_sample)
460                 tp->rcv_rtt_est.rtt = new_sample;
461 }
462
463 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
464 {
465         if (tp->rcv_rtt_est.time == 0)
466                 goto new_measure;
467         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
468                 return;
469         tcp_rcv_rtt_update(tp, jiffies - tp->rcv_rtt_est.time, 1);
470
471 new_measure:
472         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
473         tp->rcv_rtt_est.time = tcp_time_stamp;
474 }
475
476 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
477                                           const struct sk_buff *skb)
478 {
479         struct tcp_sock *tp = tcp_sk(sk);
480         if (tp->rx_opt.rcv_tsecr &&
481             (TCP_SKB_CB(skb)->end_seq -
482              TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
483                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
484 }
485
486 /*
487  * This function should be called every time data is copied to user space.
488  * It calculates the appropriate TCP receive buffer space.
489  */
490 void tcp_rcv_space_adjust(struct sock *sk)
491 {
492         struct tcp_sock *tp = tcp_sk(sk);
493         int time;
494         int space;
495
496         if (tp->rcvq_space.time == 0)
497                 goto new_measure;
498
499         time = tcp_time_stamp - tp->rcvq_space.time;
500         if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
501                 return;
502
503         space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
504
505         space = max(tp->rcvq_space.space, space);
506
507         if (tp->rcvq_space.space != space) {
508                 int rcvmem;
509
510                 tp->rcvq_space.space = space;
511
512                 if (sysctl_tcp_moderate_rcvbuf &&
513                     !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
514                         int new_clamp = space;
515
516                         /* Receive space grows, normalize in order to
517                          * take into account packet headers and sk_buff
518                          * structure overhead.
519                          */
520                         space /= tp->advmss;
521                         if (!space)
522                                 space = 1;
523                         rcvmem = (tp->advmss + MAX_TCP_HEADER +
524                                   16 + sizeof(struct sk_buff));
525                         while (tcp_win_from_space(rcvmem) < tp->advmss)
526                                 rcvmem += 128;
527                         space *= rcvmem;
528                         space = min(space, sysctl_tcp_rmem[2]);
529                         if (space > sk->sk_rcvbuf) {
530                                 sk->sk_rcvbuf = space;
531
532                                 /* Make the window clamp follow along.  */
533                                 tp->window_clamp = new_clamp;
534                         }
535                 }
536         }
537
538 new_measure:
539         tp->rcvq_space.seq = tp->copied_seq;
540         tp->rcvq_space.time = tcp_time_stamp;
541 }
542
543 /* There is something which you must keep in mind when you analyze the
544  * behavior of the tp->ato delayed ack timeout interval.  When a
545  * connection starts up, we want to ack as quickly as possible.  The
546  * problem is that "good" TCP's do slow start at the beginning of data
547  * transmission.  The means that until we send the first few ACK's the
548  * sender will sit on his end and only queue most of his data, because
549  * he can only send snd_cwnd unacked packets at any given time.  For
550  * each ACK we send, he increments snd_cwnd and transmits more of his
551  * queue.  -DaveM
552  */
553 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
554 {
555         struct tcp_sock *tp = tcp_sk(sk);
556         struct inet_connection_sock *icsk = inet_csk(sk);
557         u32 now;
558
559         inet_csk_schedule_ack(sk);
560
561         tcp_measure_rcv_mss(sk, skb);
562
563         tcp_rcv_rtt_measure(tp);
564
565         now = tcp_time_stamp;
566
567         if (!icsk->icsk_ack.ato) {
568                 /* The _first_ data packet received, initialize
569                  * delayed ACK engine.
570                  */
571                 tcp_incr_quickack(sk);
572                 icsk->icsk_ack.ato = TCP_ATO_MIN;
573         } else {
574                 int m = now - icsk->icsk_ack.lrcvtime;
575
576                 if (m <= TCP_ATO_MIN / 2) {
577                         /* The fastest case is the first. */
578                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
579                 } else if (m < icsk->icsk_ack.ato) {
580                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
581                         if (icsk->icsk_ack.ato > icsk->icsk_rto)
582                                 icsk->icsk_ack.ato = icsk->icsk_rto;
583                 } else if (m > icsk->icsk_rto) {
584                         /* Too long gap. Apparently sender failed to
585                          * restart window, so that we send ACKs quickly.
586                          */
587                         tcp_incr_quickack(sk);
588                         sk_mem_reclaim(sk);
589                 }
590         }
591         icsk->icsk_ack.lrcvtime = now;
592
593         TCP_ECN_check_ce(tp, skb);
594
595         if (skb->len >= 128)
596                 tcp_grow_window(sk, skb);
597 }
598
599 static u32 tcp_rto_min(struct sock *sk)
600 {
601         struct dst_entry *dst = __sk_dst_get(sk);
602         u32 rto_min = TCP_RTO_MIN;
603
604         if (dst && dst_metric_locked(dst, RTAX_RTO_MIN))
605                 rto_min = dst_metric_rtt(dst, RTAX_RTO_MIN);
606         return rto_min;
607 }
608
609 /* Called to compute a smoothed rtt estimate. The data fed to this
610  * routine either comes from timestamps, or from segments that were
611  * known _not_ to have been retransmitted [see Karn/Partridge
612  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
613  * piece by Van Jacobson.
614  * NOTE: the next three routines used to be one big routine.
615  * To save cycles in the RFC 1323 implementation it was better to break
616  * it up into three procedures. -- erics
617  */
618 static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
619 {
620         struct tcp_sock *tp = tcp_sk(sk);
621         long m = mrtt; /* RTT */
622
623         /*      The following amusing code comes from Jacobson's
624          *      article in SIGCOMM '88.  Note that rtt and mdev
625          *      are scaled versions of rtt and mean deviation.
626          *      This is designed to be as fast as possible
627          *      m stands for "measurement".
628          *
629          *      On a 1990 paper the rto value is changed to:
630          *      RTO = rtt + 4 * mdev
631          *
632          * Funny. This algorithm seems to be very broken.
633          * These formulae increase RTO, when it should be decreased, increase
634          * too slowly, when it should be increased quickly, decrease too quickly
635          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
636          * does not matter how to _calculate_ it. Seems, it was trap
637          * that VJ failed to avoid. 8)
638          */
639         if (m == 0)
640                 m = 1;
641         if (tp->srtt != 0) {
642                 m -= (tp->srtt >> 3);   /* m is now error in rtt est */
643                 tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
644                 if (m < 0) {
645                         m = -m;         /* m is now abs(error) */
646                         m -= (tp->mdev >> 2);   /* similar update on mdev */
647                         /* This is similar to one of Eifel findings.
648                          * Eifel blocks mdev updates when rtt decreases.
649                          * This solution is a bit different: we use finer gain
650                          * for mdev in this case (alpha*beta).
651                          * Like Eifel it also prevents growth of rto,
652                          * but also it limits too fast rto decreases,
653                          * happening in pure Eifel.
654                          */
655                         if (m > 0)
656                                 m >>= 3;
657                 } else {
658                         m -= (tp->mdev >> 2);   /* similar update on mdev */
659                 }
660                 tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
661                 if (tp->mdev > tp->mdev_max) {
662                         tp->mdev_max = tp->mdev;
663                         if (tp->mdev_max > tp->rttvar)
664                                 tp->rttvar = tp->mdev_max;
665                 }
666                 if (after(tp->snd_una, tp->rtt_seq)) {
667                         if (tp->mdev_max < tp->rttvar)
668                                 tp->rttvar -= (tp->rttvar - tp->mdev_max) >> 2;
669                         tp->rtt_seq = tp->snd_nxt;
670                         tp->mdev_max = tcp_rto_min(sk);
671                 }
672         } else {
673                 /* no previous measure. */
674                 tp->srtt = m << 3;      /* take the measured time to be rtt */
675                 tp->mdev = m << 1;      /* make sure rto = 3*rtt */
676                 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
677                 tp->rtt_seq = tp->snd_nxt;
678         }
679 }
680
681 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
682  * routine referred to above.
683  */
684 static inline void tcp_set_rto(struct sock *sk)
685 {
686         const struct tcp_sock *tp = tcp_sk(sk);
687         /* Old crap is replaced with new one. 8)
688          *
689          * More seriously:
690          * 1. If rtt variance happened to be less 50msec, it is hallucination.
691          *    It cannot be less due to utterly erratic ACK generation made
692          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
693          *    to do with delayed acks, because at cwnd>2 true delack timeout
694          *    is invisible. Actually, Linux-2.4 also generates erratic
695          *    ACKs in some circumstances.
696          */
697         inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
698
699         /* 2. Fixups made earlier cannot be right.
700          *    If we do not estimate RTO correctly without them,
701          *    all the algo is pure shit and should be replaced
702          *    with correct one. It is exactly, which we pretend to do.
703          */
704
705         /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
706          * guarantees that rto is higher.
707          */
708         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
709                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
710 }
711
712 /* Save metrics learned by this TCP session.
713    This function is called only, when TCP finishes successfully
714    i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
715  */
716 void tcp_update_metrics(struct sock *sk)
717 {
718         struct tcp_sock *tp = tcp_sk(sk);
719         struct dst_entry *dst = __sk_dst_get(sk);
720
721         if (sysctl_tcp_nometrics_save)
722                 return;
723
724         dst_confirm(dst);
725
726         if (dst && (dst->flags & DST_HOST)) {
727                 const struct inet_connection_sock *icsk = inet_csk(sk);
728                 int m;
729                 unsigned long rtt;
730
731                 if (icsk->icsk_backoff || !tp->srtt) {
732                         /* This session failed to estimate rtt. Why?
733                          * Probably, no packets returned in time.
734                          * Reset our results.
735                          */
736                         if (!(dst_metric_locked(dst, RTAX_RTT)))
737                                 dst->metrics[RTAX_RTT - 1] = 0;
738                         return;
739                 }
740
741                 rtt = dst_metric_rtt(dst, RTAX_RTT);
742                 m = rtt - tp->srtt;
743
744                 /* If newly calculated rtt larger than stored one,
745                  * store new one. Otherwise, use EWMA. Remember,
746                  * rtt overestimation is always better than underestimation.
747                  */
748                 if (!(dst_metric_locked(dst, RTAX_RTT))) {
749                         if (m <= 0)
750                                 set_dst_metric_rtt(dst, RTAX_RTT, tp->srtt);
751                         else
752                                 set_dst_metric_rtt(dst, RTAX_RTT, rtt - (m >> 3));
753                 }
754
755                 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
756                         unsigned long var;
757                         if (m < 0)
758                                 m = -m;
759
760                         /* Scale deviation to rttvar fixed point */
761                         m >>= 1;
762                         if (m < tp->mdev)
763                                 m = tp->mdev;
764
765                         var = dst_metric_rtt(dst, RTAX_RTTVAR);
766                         if (m >= var)
767                                 var = m;
768                         else
769                                 var -= (var - m) >> 2;
770
771                         set_dst_metric_rtt(dst, RTAX_RTTVAR, var);
772                 }
773
774                 if (tp->snd_ssthresh >= 0xFFFF) {
775                         /* Slow start still did not finish. */
776                         if (dst_metric(dst, RTAX_SSTHRESH) &&
777                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
778                             (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
779                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
780                         if (!dst_metric_locked(dst, RTAX_CWND) &&
781                             tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
782                                 dst->metrics[RTAX_CWND - 1] = tp->snd_cwnd;
783                 } else if (tp->snd_cwnd > tp->snd_ssthresh &&
784                            icsk->icsk_ca_state == TCP_CA_Open) {
785                         /* Cong. avoidance phase, cwnd is reliable. */
786                         if (!dst_metric_locked(dst, RTAX_SSTHRESH))
787                                 dst->metrics[RTAX_SSTHRESH-1] =
788                                         max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
789                         if (!dst_metric_locked(dst, RTAX_CWND))
790                                 dst->metrics[RTAX_CWND-1] = (dst_metric(dst, RTAX_CWND) + tp->snd_cwnd) >> 1;
791                 } else {
792                         /* Else slow start did not finish, cwnd is non-sense,
793                            ssthresh may be also invalid.
794                          */
795                         if (!dst_metric_locked(dst, RTAX_CWND))
796                                 dst->metrics[RTAX_CWND-1] = (dst_metric(dst, RTAX_CWND) + tp->snd_ssthresh) >> 1;
797                         if (dst_metric(dst, RTAX_SSTHRESH) &&
798                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
799                             tp->snd_ssthresh > dst_metric(dst, RTAX_SSTHRESH))
800                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
801                 }
802
803                 if (!dst_metric_locked(dst, RTAX_REORDERING)) {
804                         if (dst_metric(dst, RTAX_REORDERING) < tp->reordering &&
805                             tp->reordering != sysctl_tcp_reordering)
806                                 dst->metrics[RTAX_REORDERING-1] = tp->reordering;
807                 }
808         }
809 }
810
811 /* Numbers are taken from RFC3390.
812  *
813  * John Heffner states:
814  *
815  *      The RFC specifies a window of no more than 4380 bytes
816  *      unless 2*MSS > 4380.  Reading the pseudocode in the RFC
817  *      is a bit misleading because they use a clamp at 4380 bytes
818  *      rather than use a multiplier in the relevant range.
819  */
820 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
821 {
822         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
823
824         if (!cwnd) {
825                 if (tp->mss_cache > 1460)
826                         cwnd = 2;
827                 else
828                         cwnd = (tp->mss_cache > 1095) ? 3 : 4;
829         }
830         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
831 }
832
833 /* Set slow start threshold and cwnd not falling to slow start */
834 void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
835 {
836         struct tcp_sock *tp = tcp_sk(sk);
837         const struct inet_connection_sock *icsk = inet_csk(sk);
838
839         tp->prior_ssthresh = 0;
840         tp->bytes_acked = 0;
841         if (icsk->icsk_ca_state < TCP_CA_CWR) {
842                 tp->undo_marker = 0;
843                 if (set_ssthresh)
844                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
845                 tp->snd_cwnd = min(tp->snd_cwnd,
846                                    tcp_packets_in_flight(tp) + 1U);
847                 tp->snd_cwnd_cnt = 0;
848                 tp->high_seq = tp->snd_nxt;
849                 tp->snd_cwnd_stamp = tcp_time_stamp;
850                 TCP_ECN_queue_cwr(tp);
851
852                 tcp_set_ca_state(sk, TCP_CA_CWR);
853         }
854 }
855
856 /*
857  * Packet counting of FACK is based on in-order assumptions, therefore TCP
858  * disables it when reordering is detected
859  */
860 static void tcp_disable_fack(struct tcp_sock *tp)
861 {
862         /* RFC3517 uses different metric in lost marker => reset on change */
863         if (tcp_is_fack(tp))
864                 tp->lost_skb_hint = NULL;
865         tp->rx_opt.sack_ok &= ~2;
866 }
867
868 /* Take a notice that peer is sending D-SACKs */
869 static void tcp_dsack_seen(struct tcp_sock *tp)
870 {
871         tp->rx_opt.sack_ok |= 4;
872 }
873
874 /* Initialize metrics on socket. */
875
876 static void tcp_init_metrics(struct sock *sk)
877 {
878         struct tcp_sock *tp = tcp_sk(sk);
879         struct dst_entry *dst = __sk_dst_get(sk);
880
881         if (dst == NULL)
882                 goto reset;
883
884         dst_confirm(dst);
885
886         if (dst_metric_locked(dst, RTAX_CWND))
887                 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
888         if (dst_metric(dst, RTAX_SSTHRESH)) {
889                 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
890                 if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
891                         tp->snd_ssthresh = tp->snd_cwnd_clamp;
892         }
893         if (dst_metric(dst, RTAX_REORDERING) &&
894             tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
895                 tcp_disable_fack(tp);
896                 tp->reordering = dst_metric(dst, RTAX_REORDERING);
897         }
898
899         if (dst_metric(dst, RTAX_RTT) == 0)
900                 goto reset;
901
902         if (!tp->srtt && dst_metric_rtt(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
903                 goto reset;
904
905         /* Initial rtt is determined from SYN,SYN-ACK.
906          * The segment is small and rtt may appear much
907          * less than real one. Use per-dst memory
908          * to make it more realistic.
909          *
910          * A bit of theory. RTT is time passed after "normal" sized packet
911          * is sent until it is ACKed. In normal circumstances sending small
912          * packets force peer to delay ACKs and calculation is correct too.
913          * The algorithm is adaptive and, provided we follow specs, it
914          * NEVER underestimate RTT. BUT! If peer tries to make some clever
915          * tricks sort of "quick acks" for time long enough to decrease RTT
916          * to low value, and then abruptly stops to do it and starts to delay
917          * ACKs, wait for troubles.
918          */
919         if (dst_metric_rtt(dst, RTAX_RTT) > tp->srtt) {
920                 tp->srtt = dst_metric_rtt(dst, RTAX_RTT);
921                 tp->rtt_seq = tp->snd_nxt;
922         }
923         if (dst_metric_rtt(dst, RTAX_RTTVAR) > tp->mdev) {
924                 tp->mdev = dst_metric_rtt(dst, RTAX_RTTVAR);
925                 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
926         }
927         tcp_set_rto(sk);
928         if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
929                 goto reset;
930         tp->snd_cwnd = tcp_init_cwnd(tp, dst);
931         tp->snd_cwnd_stamp = tcp_time_stamp;
932         return;
933
934 reset:
935         /* Play conservative. If timestamps are not
936          * supported, TCP will fail to recalculate correct
937          * rtt, if initial rto is too small. FORGET ALL AND RESET!
938          */
939         if (!tp->rx_opt.saw_tstamp && tp->srtt) {
940                 tp->srtt = 0;
941                 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
942                 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
943         }
944 }
945
946 static void tcp_update_reordering(struct sock *sk, const int metric,
947                                   const int ts)
948 {
949         struct tcp_sock *tp = tcp_sk(sk);
950         if (metric > tp->reordering) {
951                 int mib_idx;
952
953                 tp->reordering = min(TCP_MAX_REORDERING, metric);
954
955                 /* This exciting event is worth to be remembered. 8) */
956                 if (ts)
957                         mib_idx = LINUX_MIB_TCPTSREORDER;
958                 else if (tcp_is_reno(tp))
959                         mib_idx = LINUX_MIB_TCPRENOREORDER;
960                 else if (tcp_is_fack(tp))
961                         mib_idx = LINUX_MIB_TCPFACKREORDER;
962                 else
963                         mib_idx = LINUX_MIB_TCPSACKREORDER;
964
965                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
966 #if FASTRETRANS_DEBUG > 1
967                 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
968                        tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
969                        tp->reordering,
970                        tp->fackets_out,
971                        tp->sacked_out,
972                        tp->undo_marker ? tp->undo_retrans : 0);
973 #endif
974                 tcp_disable_fack(tp);
975         }
976 }
977
978 /* This must be called before lost_out is incremented */
979 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
980 {
981         if ((tp->retransmit_skb_hint == NULL) ||
982             before(TCP_SKB_CB(skb)->seq,
983                    TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
984                 tp->retransmit_skb_hint = skb;
985
986         if (!tp->lost_out ||
987             after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
988                 tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
989 }
990
991 static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
992 {
993         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
994                 tcp_verify_retransmit_hint(tp, skb);
995
996                 tp->lost_out += tcp_skb_pcount(skb);
997                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
998         }
999 }
1000
1001 static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp,
1002                                             struct sk_buff *skb)
1003 {
1004         tcp_verify_retransmit_hint(tp, skb);
1005
1006         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1007                 tp->lost_out += tcp_skb_pcount(skb);
1008                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1009         }
1010 }
1011
1012 /* This procedure tags the retransmission queue when SACKs arrive.
1013  *
1014  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
1015  * Packets in queue with these bits set are counted in variables
1016  * sacked_out, retrans_out and lost_out, correspondingly.
1017  *
1018  * Valid combinations are:
1019  * Tag  InFlight        Description
1020  * 0    1               - orig segment is in flight.
1021  * S    0               - nothing flies, orig reached receiver.
1022  * L    0               - nothing flies, orig lost by net.
1023  * R    2               - both orig and retransmit are in flight.
1024  * L|R  1               - orig is lost, retransmit is in flight.
1025  * S|R  1               - orig reached receiver, retrans is still in flight.
1026  * (L|S|R is logically valid, it could occur when L|R is sacked,
1027  *  but it is equivalent to plain S and code short-curcuits it to S.
1028  *  L|S is logically invalid, it would mean -1 packet in flight 8))
1029  *
1030  * These 6 states form finite state machine, controlled by the following events:
1031  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
1032  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
1033  * 3. Loss detection event of one of three flavors:
1034  *      A. Scoreboard estimator decided the packet is lost.
1035  *         A'. Reno "three dupacks" marks head of queue lost.
1036  *         A''. Its FACK modfication, head until snd.fack is lost.
1037  *      B. SACK arrives sacking data transmitted after never retransmitted
1038  *         hole was sent out.
1039  *      C. SACK arrives sacking SND.NXT at the moment, when the
1040  *         segment was retransmitted.
1041  * 4. D-SACK added new rule: D-SACK changes any tag to S.
1042  *
1043  * It is pleasant to note, that state diagram turns out to be commutative,
1044  * so that we are allowed not to be bothered by order of our actions,
1045  * when multiple events arrive simultaneously. (see the function below).
1046  *
1047  * Reordering detection.
1048  * --------------------
1049  * Reordering metric is maximal distance, which a packet can be displaced
1050  * in packet stream. With SACKs we can estimate it:
1051  *
1052  * 1. SACK fills old hole and the corresponding segment was not
1053  *    ever retransmitted -> reordering. Alas, we cannot use it
1054  *    when segment was retransmitted.
1055  * 2. The last flaw is solved with D-SACK. D-SACK arrives
1056  *    for retransmitted and already SACKed segment -> reordering..
1057  * Both of these heuristics are not used in Loss state, when we cannot
1058  * account for retransmits accurately.
1059  *
1060  * SACK block validation.
1061  * ----------------------
1062  *
1063  * SACK block range validation checks that the received SACK block fits to
1064  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1065  * Note that SND.UNA is not included to the range though being valid because
1066  * it means that the receiver is rather inconsistent with itself reporting
1067  * SACK reneging when it should advance SND.UNA. Such SACK block this is
1068  * perfectly valid, however, in light of RFC2018 which explicitly states
1069  * that "SACK block MUST reflect the newest segment.  Even if the newest
1070  * segment is going to be discarded ...", not that it looks very clever
1071  * in case of head skb. Due to potentional receiver driven attacks, we
1072  * choose to avoid immediate execution of a walk in write queue due to
1073  * reneging and defer head skb's loss recovery to standard loss recovery
1074  * procedure that will eventually trigger (nothing forbids us doing this).
1075  *
1076  * Implements also blockage to start_seq wrap-around. Problem lies in the
1077  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1078  * there's no guarantee that it will be before snd_nxt (n). The problem
1079  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1080  * wrap (s_w):
1081  *
1082  *         <- outs wnd ->                          <- wrapzone ->
1083  *         u     e      n                         u_w   e_w  s n_w
1084  *         |     |      |                          |     |   |  |
1085  * |<------------+------+----- TCP seqno space --------------+---------->|
1086  * ...-- <2^31 ->|                                           |<--------...
1087  * ...---- >2^31 ------>|                                    |<--------...
1088  *
1089  * Current code wouldn't be vulnerable but it's better still to discard such
1090  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1091  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1092  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1093  * equal to the ideal case (infinite seqno space without wrap caused issues).
1094  *
1095  * With D-SACK the lower bound is extended to cover sequence space below
1096  * SND.UNA down to undo_marker, which is the last point of interest. Yet
1097  * again, D-SACK block must not to go across snd_una (for the same reason as
1098  * for the normal SACK blocks, explained above). But there all simplicity
1099  * ends, TCP might receive valid D-SACKs below that. As long as they reside
1100  * fully below undo_marker they do not affect behavior in anyway and can
1101  * therefore be safely ignored. In rare cases (which are more or less
1102  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1103  * fragmentation and packet reordering past skb's retransmission. To consider
1104  * them correctly, the acceptable range must be extended even more though
1105  * the exact amount is rather hard to quantify. However, tp->max_window can
1106  * be used as an exaggerated estimate.
1107  */
1108 static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack,
1109                                   u32 start_seq, u32 end_seq)
1110 {
1111         /* Too far in future, or reversed (interpretation is ambiguous) */
1112         if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1113                 return 0;
1114
1115         /* Nasty start_seq wrap-around check (see comments above) */
1116         if (!before(start_seq, tp->snd_nxt))
1117                 return 0;
1118
1119         /* In outstanding window? ...This is valid exit for D-SACKs too.
1120          * start_seq == snd_una is non-sensical (see comments above)
1121          */
1122         if (after(start_seq, tp->snd_una))
1123                 return 1;
1124
1125         if (!is_dsack || !tp->undo_marker)
1126                 return 0;
1127
1128         /* ...Then it's D-SACK, and must reside below snd_una completely */
1129         if (!after(end_seq, tp->snd_una))
1130                 return 0;
1131
1132         if (!before(start_seq, tp->undo_marker))
1133                 return 1;
1134
1135         /* Too old */
1136         if (!after(end_seq, tp->undo_marker))
1137                 return 0;
1138
1139         /* Undo_marker boundary crossing (overestimates a lot). Known already:
1140          *   start_seq < undo_marker and end_seq >= undo_marker.
1141          */
1142         return !before(start_seq, end_seq - tp->max_window);
1143 }
1144
1145 /* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
1146  * Event "C". Later note: FACK people cheated me again 8), we have to account
1147  * for reordering! Ugly, but should help.
1148  *
1149  * Search retransmitted skbs from write_queue that were sent when snd_nxt was
1150  * less than what is now known to be received by the other end (derived from
1151  * highest SACK block). Also calculate the lowest snd_nxt among the remaining
1152  * retransmitted skbs to avoid some costly processing per ACKs.
1153  */
1154 static void tcp_mark_lost_retrans(struct sock *sk)
1155 {
1156         const struct inet_connection_sock *icsk = inet_csk(sk);
1157         struct tcp_sock *tp = tcp_sk(sk);
1158         struct sk_buff *skb;
1159         int cnt = 0;
1160         u32 new_low_seq = tp->snd_nxt;
1161         u32 received_upto = tcp_highest_sack_seq(tp);
1162
1163         if (!tcp_is_fack(tp) || !tp->retrans_out ||
1164             !after(received_upto, tp->lost_retrans_low) ||
1165             icsk->icsk_ca_state != TCP_CA_Recovery)
1166                 return;
1167
1168         tcp_for_write_queue(skb, sk) {
1169                 u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
1170
1171                 if (skb == tcp_send_head(sk))
1172                         break;
1173                 if (cnt == tp->retrans_out)
1174                         break;
1175                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1176                         continue;
1177
1178                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
1179                         continue;
1180
1181                 if (after(received_upto, ack_seq) &&
1182                     (tcp_is_fack(tp) ||
1183                      !before(received_upto,
1184                              ack_seq + tp->reordering * tp->mss_cache))) {
1185                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1186                         tp->retrans_out -= tcp_skb_pcount(skb);
1187
1188                         tcp_skb_mark_lost_uncond_verify(tp, skb);
1189                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT);
1190                 } else {
1191                         if (before(ack_seq, new_low_seq))
1192                                 new_low_seq = ack_seq;
1193                         cnt += tcp_skb_pcount(skb);
1194                 }
1195         }
1196
1197         if (tp->retrans_out)
1198                 tp->lost_retrans_low = new_low_seq;
1199 }
1200
1201 static int tcp_check_dsack(struct sock *sk, struct sk_buff *ack_skb,
1202                            struct tcp_sack_block_wire *sp, int num_sacks,
1203                            u32 prior_snd_una)
1204 {
1205         struct tcp_sock *tp = tcp_sk(sk);
1206         u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1207         u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1208         int dup_sack = 0;
1209
1210         if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1211                 dup_sack = 1;
1212                 tcp_dsack_seen(tp);
1213                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1214         } else if (num_sacks > 1) {
1215                 u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1216                 u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1217
1218                 if (!after(end_seq_0, end_seq_1) &&
1219                     !before(start_seq_0, start_seq_1)) {
1220                         dup_sack = 1;
1221                         tcp_dsack_seen(tp);
1222                         NET_INC_STATS_BH(sock_net(sk),
1223                                         LINUX_MIB_TCPDSACKOFORECV);
1224                 }
1225         }
1226
1227         /* D-SACK for already forgotten data... Do dumb counting. */
1228         if (dup_sack &&
1229             !after(end_seq_0, prior_snd_una) &&
1230             after(end_seq_0, tp->undo_marker))
1231                 tp->undo_retrans--;
1232
1233         return dup_sack;
1234 }
1235
1236 struct tcp_sacktag_state {
1237         int reord;
1238         int fack_count;
1239         int flag;
1240 };
1241
1242 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1243  * the incoming SACK may not exactly match but we can find smaller MSS
1244  * aligned portion of it that matches. Therefore we might need to fragment
1245  * which may fail and creates some hassle (caller must handle error case
1246  * returns).
1247  *
1248  * FIXME: this could be merged to shift decision code
1249  */
1250 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1251                                  u32 start_seq, u32 end_seq)
1252 {
1253         int in_sack, err;
1254         unsigned int pkt_len;
1255         unsigned int mss;
1256
1257         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1258                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1259
1260         if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1261             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1262                 mss = tcp_skb_mss(skb);
1263                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1264
1265                 if (!in_sack) {
1266                         pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1267                         if (pkt_len < mss)
1268                                 pkt_len = mss;
1269                 } else {
1270                         pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1271                         if (pkt_len < mss)
1272                                 return -EINVAL;
1273                 }
1274
1275                 /* Round if necessary so that SACKs cover only full MSSes
1276                  * and/or the remaining small portion (if present)
1277                  */
1278                 if (pkt_len > mss) {
1279                         unsigned int new_len = (pkt_len / mss) * mss;
1280                         if (!in_sack && new_len < pkt_len) {
1281                                 new_len += mss;
1282                                 if (new_len > skb->len)
1283                                         return 0;
1284                         }
1285                         pkt_len = new_len;
1286                 }
1287                 err = tcp_fragment(sk, skb, pkt_len, mss);
1288                 if (err < 0)
1289                         return err;
1290         }
1291
1292         return in_sack;
1293 }
1294
1295 static u8 tcp_sacktag_one(struct sk_buff *skb, struct sock *sk,
1296                           struct tcp_sacktag_state *state,
1297                           int dup_sack, int pcount)
1298 {
1299         struct tcp_sock *tp = tcp_sk(sk);
1300         u8 sacked = TCP_SKB_CB(skb)->sacked;
1301         int fack_count = state->fack_count;
1302
1303         /* Account D-SACK for retransmitted packet. */
1304         if (dup_sack && (sacked & TCPCB_RETRANS)) {
1305                 if (after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1306                         tp->undo_retrans--;
1307                 if (sacked & TCPCB_SACKED_ACKED)
1308                         state->reord = min(fack_count, state->reord);
1309         }
1310
1311         /* Nothing to do; acked frame is about to be dropped (was ACKed). */
1312         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1313                 return sacked;
1314
1315         if (!(sacked & TCPCB_SACKED_ACKED)) {
1316                 if (sacked & TCPCB_SACKED_RETRANS) {
1317                         /* If the segment is not tagged as lost,
1318                          * we do not clear RETRANS, believing
1319                          * that retransmission is still in flight.
1320                          */
1321                         if (sacked & TCPCB_LOST) {
1322                                 sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1323                                 tp->lost_out -= pcount;
1324                                 tp->retrans_out -= pcount;
1325                         }
1326                 } else {
1327                         if (!(sacked & TCPCB_RETRANS)) {
1328                                 /* New sack for not retransmitted frame,
1329                                  * which was in hole. It is reordering.
1330                                  */
1331                                 if (before(TCP_SKB_CB(skb)->seq,
1332                                            tcp_highest_sack_seq(tp)))
1333                                         state->reord = min(fack_count,
1334                                                            state->reord);
1335
1336                                 /* SACK enhanced F-RTO (RFC4138; Appendix B) */
1337                                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark))
1338                                         state->flag |= FLAG_ONLY_ORIG_SACKED;
1339                         }
1340
1341                         if (sacked & TCPCB_LOST) {
1342                                 sacked &= ~TCPCB_LOST;
1343                                 tp->lost_out -= pcount;
1344                         }
1345                 }
1346
1347                 sacked |= TCPCB_SACKED_ACKED;
1348                 state->flag |= FLAG_DATA_SACKED;
1349                 tp->sacked_out += pcount;
1350
1351                 fack_count += pcount;
1352
1353                 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1354                 if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) &&
1355                     before(TCP_SKB_CB(skb)->seq,
1356                            TCP_SKB_CB(tp->lost_skb_hint)->seq))
1357                         tp->lost_cnt_hint += pcount;
1358
1359                 if (fack_count > tp->fackets_out)
1360                         tp->fackets_out = fack_count;
1361         }
1362
1363         /* D-SACK. We can detect redundant retransmission in S|R and plain R
1364          * frames and clear it. undo_retrans is decreased above, L|R frames
1365          * are accounted above as well.
1366          */
1367         if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1368                 sacked &= ~TCPCB_SACKED_RETRANS;
1369                 tp->retrans_out -= pcount;
1370         }
1371
1372         return sacked;
1373 }
1374
1375 static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
1376                            struct tcp_sacktag_state *state,
1377                            unsigned int pcount, int shifted, int mss,
1378                            int dup_sack)
1379 {
1380         struct tcp_sock *tp = tcp_sk(sk);
1381         struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
1382
1383         BUG_ON(!pcount);
1384
1385         /* Tweak before seqno plays */
1386         if (!tcp_is_fack(tp) && tcp_is_sack(tp) && tp->lost_skb_hint &&
1387             !before(TCP_SKB_CB(tp->lost_skb_hint)->seq, TCP_SKB_CB(skb)->seq))
1388                 tp->lost_cnt_hint += pcount;
1389
1390         TCP_SKB_CB(prev)->end_seq += shifted;
1391         TCP_SKB_CB(skb)->seq += shifted;
1392
1393         skb_shinfo(prev)->gso_segs += pcount;
1394         BUG_ON(skb_shinfo(skb)->gso_segs < pcount);
1395         skb_shinfo(skb)->gso_segs -= pcount;
1396
1397         /* When we're adding to gso_segs == 1, gso_size will be zero,
1398          * in theory this shouldn't be necessary but as long as DSACK
1399          * code can come after this skb later on it's better to keep
1400          * setting gso_size to something.
1401          */
1402         if (!skb_shinfo(prev)->gso_size) {
1403                 skb_shinfo(prev)->gso_size = mss;
1404                 skb_shinfo(prev)->gso_type = sk->sk_gso_type;
1405         }
1406
1407         /* CHECKME: To clear or not to clear? Mimics normal skb currently */
1408         if (skb_shinfo(skb)->gso_segs <= 1) {
1409                 skb_shinfo(skb)->gso_size = 0;
1410                 skb_shinfo(skb)->gso_type = 0;
1411         }
1412
1413         /* We discard results */
1414         tcp_sacktag_one(skb, sk, state, dup_sack, pcount);
1415
1416         /* Difference in this won't matter, both ACKed by the same cumul. ACK */
1417         TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1418
1419         if (skb->len > 0) {
1420                 BUG_ON(!tcp_skb_pcount(skb));
1421                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1422                 return 0;
1423         }
1424
1425         /* Whole SKB was eaten :-) */
1426
1427         if (skb == tp->retransmit_skb_hint)
1428                 tp->retransmit_skb_hint = prev;
1429         if (skb == tp->scoreboard_skb_hint)
1430                 tp->scoreboard_skb_hint = prev;
1431         if (skb == tp->lost_skb_hint) {
1432                 tp->lost_skb_hint = prev;
1433                 tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1434         }
1435
1436         TCP_SKB_CB(skb)->flags |= TCP_SKB_CB(prev)->flags;
1437         if (skb == tcp_highest_sack(sk))
1438                 tcp_advance_highest_sack(sk, skb);
1439
1440         tcp_unlink_write_queue(skb, sk);
1441         sk_wmem_free_skb(sk, skb);
1442
1443         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
1444
1445         return 1;
1446 }
1447
1448 /* I wish gso_size would have a bit more sane initialization than
1449  * something-or-zero which complicates things
1450  */
1451 static int tcp_skb_seglen(struct sk_buff *skb)
1452 {
1453         return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1454 }
1455
1456 /* Shifting pages past head area doesn't work */
1457 static int skb_can_shift(struct sk_buff *skb)
1458 {
1459         return !skb_headlen(skb) && skb_is_nonlinear(skb);
1460 }
1461
1462 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1463  * skb.
1464  */
1465 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1466                                           struct tcp_sacktag_state *state,
1467                                           u32 start_seq, u32 end_seq,
1468                                           int dup_sack)
1469 {
1470         struct tcp_sock *tp = tcp_sk(sk);
1471         struct sk_buff *prev;
1472         int mss;
1473         int pcount = 0;
1474         int len;
1475         int in_sack;
1476
1477         if (!sk_can_gso(sk))
1478                 goto fallback;
1479
1480         /* Normally R but no L won't result in plain S */
1481         if (!dup_sack &&
1482             (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1483                 goto fallback;
1484         if (!skb_can_shift(skb))
1485                 goto fallback;
1486         /* This frame is about to be dropped (was ACKed). */
1487         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1488                 goto fallback;
1489
1490         /* Can only happen with delayed DSACK + discard craziness */
1491         if (unlikely(skb == tcp_write_queue_head(sk)))
1492                 goto fallback;
1493         prev = tcp_write_queue_prev(sk, skb);
1494
1495         if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1496                 goto fallback;
1497
1498         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1499                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1500
1501         if (in_sack) {
1502                 len = skb->len;
1503                 pcount = tcp_skb_pcount(skb);
1504                 mss = tcp_skb_seglen(skb);
1505
1506                 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1507                  * drop this restriction as unnecessary
1508                  */
1509                 if (mss != tcp_skb_seglen(prev))
1510                         goto fallback;
1511         } else {
1512                 if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1513                         goto noop;
1514                 /* CHECKME: This is non-MSS split case only?, this will
1515                  * cause skipped skbs due to advancing loop btw, original
1516                  * has that feature too
1517                  */
1518                 if (tcp_skb_pcount(skb) <= 1)
1519                         goto noop;
1520
1521                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1522                 if (!in_sack) {
1523                         /* TODO: head merge to next could be attempted here
1524                          * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1525                          * though it might not be worth of the additional hassle
1526                          *
1527                          * ...we can probably just fallback to what was done
1528                          * previously. We could try merging non-SACKed ones
1529                          * as well but it probably isn't going to buy off
1530                          * because later SACKs might again split them, and
1531                          * it would make skb timestamp tracking considerably
1532                          * harder problem.
1533                          */
1534                         goto fallback;
1535                 }
1536
1537                 len = end_seq - TCP_SKB_CB(skb)->seq;
1538                 BUG_ON(len < 0);
1539                 BUG_ON(len > skb->len);
1540
1541                 /* MSS boundaries should be honoured or else pcount will
1542                  * severely break even though it makes things bit trickier.
1543                  * Optimize common case to avoid most of the divides
1544                  */
1545                 mss = tcp_skb_mss(skb);
1546
1547                 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1548                  * drop this restriction as unnecessary
1549                  */
1550                 if (mss != tcp_skb_seglen(prev))
1551                         goto fallback;
1552
1553                 if (len == mss) {
1554                         pcount = 1;
1555                 } else if (len < mss) {
1556                         goto noop;
1557                 } else {
1558                         pcount = len / mss;
1559                         len = pcount * mss;
1560                 }
1561         }
1562
1563         if (!skb_shift(prev, skb, len))
1564                 goto fallback;
1565         if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1566                 goto out;
1567
1568         /* Hole filled allows collapsing with the next as well, this is very
1569          * useful when hole on every nth skb pattern happens
1570          */
1571         if (prev == tcp_write_queue_tail(sk))
1572                 goto out;
1573         skb = tcp_write_queue_next(sk, prev);
1574
1575         if (!skb_can_shift(skb) ||
1576             (skb == tcp_send_head(sk)) ||
1577             ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1578             (mss != tcp_skb_seglen(skb)))
1579                 goto out;
1580
1581         len = skb->len;
1582         if (skb_shift(prev, skb, len)) {
1583                 pcount += tcp_skb_pcount(skb);
1584                 tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1585         }
1586
1587 out:
1588         state->fack_count += pcount;
1589         return prev;
1590
1591 noop:
1592         return skb;
1593
1594 fallback:
1595         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1596         return NULL;
1597 }
1598
1599 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1600                                         struct tcp_sack_block *next_dup,
1601                                         struct tcp_sacktag_state *state,
1602                                         u32 start_seq, u32 end_seq,
1603                                         int dup_sack_in)
1604 {
1605         struct tcp_sock *tp = tcp_sk(sk);
1606         struct sk_buff *tmp;
1607
1608         tcp_for_write_queue_from(skb, sk) {
1609                 int in_sack = 0;
1610                 int dup_sack = dup_sack_in;
1611
1612                 if (skb == tcp_send_head(sk))
1613                         break;
1614
1615                 /* queue is in-order => we can short-circuit the walk early */
1616                 if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1617                         break;
1618
1619                 if ((next_dup != NULL) &&
1620                     before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1621                         in_sack = tcp_match_skb_to_sack(sk, skb,
1622                                                         next_dup->start_seq,
1623                                                         next_dup->end_seq);
1624                         if (in_sack > 0)
1625                                 dup_sack = 1;
1626                 }
1627
1628                 /* skb reference here is a bit tricky to get right, since
1629                  * shifting can eat and free both this skb and the next,
1630                  * so not even _safe variant of the loop is enough.
1631                  */
1632                 if (in_sack <= 0) {
1633                         tmp = tcp_shift_skb_data(sk, skb, state,
1634                                                  start_seq, end_seq, dup_sack);
1635                         if (tmp != NULL) {
1636                                 if (tmp != skb) {
1637                                         skb = tmp;
1638                                         continue;
1639                                 }
1640
1641                                 in_sack = 0;
1642                         } else {
1643                                 in_sack = tcp_match_skb_to_sack(sk, skb,
1644                                                                 start_seq,
1645                                                                 end_seq);
1646                         }
1647                 }
1648
1649                 if (unlikely(in_sack < 0))
1650                         break;
1651
1652                 if (in_sack) {
1653                         TCP_SKB_CB(skb)->sacked = tcp_sacktag_one(skb, sk,
1654                                                                   state,
1655                                                                   dup_sack,
1656                                                                   tcp_skb_pcount(skb));
1657
1658                         if (!before(TCP_SKB_CB(skb)->seq,
1659                                     tcp_highest_sack_seq(tp)))
1660                                 tcp_advance_highest_sack(sk, skb);
1661                 }
1662
1663                 state->fack_count += tcp_skb_pcount(skb);
1664         }
1665         return skb;
1666 }
1667
1668 /* Avoid all extra work that is being done by sacktag while walking in
1669  * a normal way
1670  */
1671 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1672                                         struct tcp_sacktag_state *state,
1673                                         u32 skip_to_seq)
1674 {
1675         tcp_for_write_queue_from(skb, sk) {
1676                 if (skb == tcp_send_head(sk))
1677                         break;
1678
1679                 if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1680                         break;
1681
1682                 state->fack_count += tcp_skb_pcount(skb);
1683         }
1684         return skb;
1685 }
1686
1687 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1688                                                 struct sock *sk,
1689                                                 struct tcp_sack_block *next_dup,
1690                                                 struct tcp_sacktag_state *state,
1691                                                 u32 skip_to_seq)
1692 {
1693         if (next_dup == NULL)
1694                 return skb;
1695
1696         if (before(next_dup->start_seq, skip_to_seq)) {
1697                 skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1698                 skb = tcp_sacktag_walk(skb, sk, NULL, state,
1699                                        next_dup->start_seq, next_dup->end_seq,
1700                                        1);
1701         }
1702
1703         return skb;
1704 }
1705
1706 static int tcp_sack_cache_ok(struct tcp_sock *tp, struct tcp_sack_block *cache)
1707 {
1708         return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1709 }
1710
1711 static int
1712 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb,
1713                         u32 prior_snd_una)
1714 {
1715         const struct inet_connection_sock *icsk = inet_csk(sk);
1716         struct tcp_sock *tp = tcp_sk(sk);
1717         unsigned char *ptr = (skb_transport_header(ack_skb) +
1718                               TCP_SKB_CB(ack_skb)->sacked);
1719         struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1720         struct tcp_sack_block sp[TCP_NUM_SACKS];
1721         struct tcp_sack_block *cache;
1722         struct tcp_sacktag_state state;
1723         struct sk_buff *skb;
1724         int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1725         int used_sacks;
1726         int found_dup_sack = 0;
1727         int i, j;
1728         int first_sack_index;
1729
1730         state.flag = 0;
1731         state.reord = tp->packets_out;
1732
1733         if (!tp->sacked_out) {
1734                 if (WARN_ON(tp->fackets_out))
1735                         tp->fackets_out = 0;
1736                 tcp_highest_sack_reset(sk);
1737         }
1738
1739         found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1740                                          num_sacks, prior_snd_una);
1741         if (found_dup_sack)
1742                 state.flag |= FLAG_DSACKING_ACK;
1743
1744         /* Eliminate too old ACKs, but take into
1745          * account more or less fresh ones, they can
1746          * contain valid SACK info.
1747          */
1748         if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1749                 return 0;
1750
1751         if (!tp->packets_out)
1752                 goto out;
1753
1754         used_sacks = 0;
1755         first_sack_index = 0;
1756         for (i = 0; i < num_sacks; i++) {
1757                 int dup_sack = !i && found_dup_sack;
1758
1759                 sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1760                 sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1761
1762                 if (!tcp_is_sackblock_valid(tp, dup_sack,
1763                                             sp[used_sacks].start_seq,
1764                                             sp[used_sacks].end_seq)) {
1765                         int mib_idx;
1766
1767                         if (dup_sack) {
1768                                 if (!tp->undo_marker)
1769                                         mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1770                                 else
1771                                         mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1772                         } else {
1773                                 /* Don't count olds caused by ACK reordering */
1774                                 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1775                                     !after(sp[used_sacks].end_seq, tp->snd_una))
1776                                         continue;
1777                                 mib_idx = LINUX_MIB_TCPSACKDISCARD;
1778                         }
1779
1780                         NET_INC_STATS_BH(sock_net(sk), mib_idx);
1781                         if (i == 0)
1782                                 first_sack_index = -1;
1783                         continue;
1784                 }
1785
1786                 /* Ignore very old stuff early */
1787                 if (!after(sp[used_sacks].end_seq, prior_snd_una))
1788                         continue;
1789
1790                 used_sacks++;
1791         }
1792
1793         /* order SACK blocks to allow in order walk of the retrans queue */
1794         for (i = used_sacks - 1; i > 0; i--) {
1795                 for (j = 0; j < i; j++) {
1796                         if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1797                                 struct tcp_sack_block tmp;
1798
1799                                 tmp = sp[j];
1800                                 sp[j] = sp[j + 1];
1801                                 sp[j + 1] = tmp;
1802
1803                                 /* Track where the first SACK block goes to */
1804                                 if (j == first_sack_index)
1805                                         first_sack_index = j + 1;
1806                         }
1807                 }
1808         }
1809
1810         skb = tcp_write_queue_head(sk);
1811         state.fack_count = 0;
1812         i = 0;
1813
1814         if (!tp->sacked_out) {
1815                 /* It's already past, so skip checking against it */
1816                 cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1817         } else {
1818                 cache = tp->recv_sack_cache;
1819                 /* Skip empty blocks in at head of the cache */
1820                 while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1821                        !cache->end_seq)
1822                         cache++;
1823         }
1824
1825         while (i < used_sacks) {
1826                 u32 start_seq = sp[i].start_seq;
1827                 u32 end_seq = sp[i].end_seq;
1828                 int dup_sack = (found_dup_sack && (i == first_sack_index));
1829                 struct tcp_sack_block *next_dup = NULL;
1830
1831                 if (found_dup_sack && ((i + 1) == first_sack_index))
1832                         next_dup = &sp[i + 1];
1833
1834                 /* Event "B" in the comment above. */
1835                 if (after(end_seq, tp->high_seq))
1836                         state.flag |= FLAG_DATA_LOST;
1837
1838                 /* Skip too early cached blocks */
1839                 while (tcp_sack_cache_ok(tp, cache) &&
1840                        !before(start_seq, cache->end_seq))
1841                         cache++;
1842
1843                 /* Can skip some work by looking recv_sack_cache? */
1844                 if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1845                     after(end_seq, cache->start_seq)) {
1846
1847                         /* Head todo? */
1848                         if (before(start_seq, cache->start_seq)) {
1849                                 skb = tcp_sacktag_skip(skb, sk, &state,
1850                                                        start_seq);
1851                                 skb = tcp_sacktag_walk(skb, sk, next_dup,
1852                                                        &state,
1853                                                        start_seq,
1854                                                        cache->start_seq,
1855                                                        dup_sack);
1856                         }
1857
1858                         /* Rest of the block already fully processed? */
1859                         if (!after(end_seq, cache->end_seq))
1860                                 goto advance_sp;
1861
1862                         skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1863                                                        &state,
1864                                                        cache->end_seq);
1865
1866                         /* ...tail remains todo... */
1867                         if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1868                                 /* ...but better entrypoint exists! */
1869                                 skb = tcp_highest_sack(sk);
1870                                 if (skb == NULL)
1871                                         break;
1872                                 state.fack_count = tp->fackets_out;
1873                                 cache++;
1874                                 goto walk;
1875                         }
1876
1877                         skb = tcp_sacktag_skip(skb, sk, &state, cache->end_seq);
1878                         /* Check overlap against next cached too (past this one already) */
1879                         cache++;
1880                         continue;
1881                 }
1882
1883                 if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1884                         skb = tcp_highest_sack(sk);
1885                         if (skb == NULL)
1886                                 break;
1887                         state.fack_count = tp->fackets_out;
1888                 }
1889                 skb = tcp_sacktag_skip(skb, sk, &state, start_seq);
1890
1891 walk:
1892                 skb = tcp_sacktag_walk(skb, sk, next_dup, &state,
1893                                        start_seq, end_seq, dup_sack);
1894
1895 advance_sp:
1896                 /* SACK enhanced FRTO (RFC4138, Appendix B): Clearing correct
1897                  * due to in-order walk
1898                  */
1899                 if (after(end_seq, tp->frto_highmark))
1900                         state.flag &= ~FLAG_ONLY_ORIG_SACKED;
1901
1902                 i++;
1903         }
1904
1905         /* Clear the head of the cache sack blocks so we can skip it next time */
1906         for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1907                 tp->recv_sack_cache[i].start_seq = 0;
1908                 tp->recv_sack_cache[i].end_seq = 0;
1909         }
1910         for (j = 0; j < used_sacks; j++)
1911                 tp->recv_sack_cache[i++] = sp[j];
1912
1913         tcp_mark_lost_retrans(sk);
1914
1915         tcp_verify_left_out(tp);
1916
1917         if ((state.reord < tp->fackets_out) &&
1918             ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) &&
1919             (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
1920                 tcp_update_reordering(sk, tp->fackets_out - state.reord, 0);
1921
1922 out:
1923
1924 #if FASTRETRANS_DEBUG > 0
1925         WARN_ON((int)tp->sacked_out < 0);
1926         WARN_ON((int)tp->lost_out < 0);
1927         WARN_ON((int)tp->retrans_out < 0);
1928         WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1929 #endif
1930         return state.flag;
1931 }
1932
1933 /* Limits sacked_out so that sum with lost_out isn't ever larger than
1934  * packets_out. Returns zero if sacked_out adjustement wasn't necessary.
1935  */
1936 static int tcp_limit_reno_sacked(struct tcp_sock *tp)
1937 {
1938         u32 holes;
1939
1940         holes = max(tp->lost_out, 1U);
1941         holes = min(holes, tp->packets_out);
1942
1943         if ((tp->sacked_out + holes) > tp->packets_out) {
1944                 tp->sacked_out = tp->packets_out - holes;
1945                 return 1;
1946         }
1947         return 0;
1948 }
1949
1950 /* If we receive more dupacks than we expected counting segments
1951  * in assumption of absent reordering, interpret this as reordering.
1952  * The only another reason could be bug in receiver TCP.
1953  */
1954 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1955 {
1956         struct tcp_sock *tp = tcp_sk(sk);
1957         if (tcp_limit_reno_sacked(tp))
1958                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1959 }
1960
1961 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1962
1963 static void tcp_add_reno_sack(struct sock *sk)
1964 {
1965         struct tcp_sock *tp = tcp_sk(sk);
1966         tp->sacked_out++;
1967         tcp_check_reno_reordering(sk, 0);
1968         tcp_verify_left_out(tp);
1969 }
1970
1971 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1972
1973 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1974 {
1975         struct tcp_sock *tp = tcp_sk(sk);
1976
1977         if (acked > 0) {
1978                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1979                 if (acked - 1 >= tp->sacked_out)
1980                         tp->sacked_out = 0;
1981                 else
1982                         tp->sacked_out -= acked - 1;
1983         }
1984         tcp_check_reno_reordering(sk, acked);
1985         tcp_verify_left_out(tp);
1986 }
1987
1988 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1989 {
1990         tp->sacked_out = 0;
1991 }
1992
1993 static int tcp_is_sackfrto(const struct tcp_sock *tp)
1994 {
1995         return (sysctl_tcp_frto == 0x2) && !tcp_is_reno(tp);
1996 }
1997
1998 /* F-RTO can only be used if TCP has never retransmitted anything other than
1999  * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
2000  */
2001 int tcp_use_frto(struct sock *sk)
2002 {
2003         const struct tcp_sock *tp = tcp_sk(sk);
2004         const struct inet_connection_sock *icsk = inet_csk(sk);
2005         struct sk_buff *skb;
2006
2007         if (!sysctl_tcp_frto)
2008                 return 0;
2009
2010         /* MTU probe and F-RTO won't really play nicely along currently */
2011         if (icsk->icsk_mtup.probe_size)
2012                 return 0;
2013
2014         if (tcp_is_sackfrto(tp))
2015                 return 1;
2016
2017         /* Avoid expensive walking of rexmit queue if possible */
2018         if (tp->retrans_out > 1)
2019                 return 0;
2020
2021         skb = tcp_write_queue_head(sk);
2022         if (tcp_skb_is_last(sk, skb))
2023                 return 1;
2024         skb = tcp_write_queue_next(sk, skb);    /* Skips head */
2025         tcp_for_write_queue_from(skb, sk) {
2026                 if (skb == tcp_send_head(sk))
2027                         break;
2028                 if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2029                         return 0;
2030                 /* Short-circuit when first non-SACKed skb has been checked */
2031                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2032                         break;
2033         }
2034         return 1;
2035 }
2036
2037 /* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
2038  * recovery a bit and use heuristics in tcp_process_frto() to detect if
2039  * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
2040  * keep retrans_out counting accurate (with SACK F-RTO, other than head
2041  * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
2042  * bits are handled if the Loss state is really to be entered (in
2043  * tcp_enter_frto_loss).
2044  *
2045  * Do like tcp_enter_loss() would; when RTO expires the second time it
2046  * does:
2047  *  "Reduce ssthresh if it has not yet been made inside this window."
2048  */
2049 void tcp_enter_frto(struct sock *sk)
2050 {
2051         const struct inet_connection_sock *icsk = inet_csk(sk);
2052         struct tcp_sock *tp = tcp_sk(sk);
2053         struct sk_buff *skb;
2054
2055         if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
2056             tp->snd_una == tp->high_seq ||
2057             ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
2058              !icsk->icsk_retransmits)) {
2059                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2060                 /* Our state is too optimistic in ssthresh() call because cwnd
2061                  * is not reduced until tcp_enter_frto_loss() when previous F-RTO
2062                  * recovery has not yet completed. Pattern would be this: RTO,
2063                  * Cumulative ACK, RTO (2xRTO for the same segment does not end
2064                  * up here twice).
2065                  * RFC4138 should be more specific on what to do, even though
2066                  * RTO is quite unlikely to occur after the first Cumulative ACK
2067                  * due to back-off and complexity of triggering events ...
2068                  */
2069                 if (tp->frto_counter) {
2070                         u32 stored_cwnd;
2071                         stored_cwnd = tp->snd_cwnd;
2072                         tp->snd_cwnd = 2;
2073                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2074                         tp->snd_cwnd = stored_cwnd;
2075                 } else {
2076                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2077                 }
2078                 /* ... in theory, cong.control module could do "any tricks" in
2079                  * ssthresh(), which means that ca_state, lost bits and lost_out
2080                  * counter would have to be faked before the call occurs. We
2081                  * consider that too expensive, unlikely and hacky, so modules
2082                  * using these in ssthresh() must deal these incompatibility
2083                  * issues if they receives CA_EVENT_FRTO and frto_counter != 0
2084                  */
2085                 tcp_ca_event(sk, CA_EVENT_FRTO);
2086         }
2087
2088         tp->undo_marker = tp->snd_una;
2089         tp->undo_retrans = 0;
2090
2091         skb = tcp_write_queue_head(sk);
2092         if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2093                 tp->undo_marker = 0;
2094         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2095                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2096                 tp->retrans_out -= tcp_skb_pcount(skb);
2097         }
2098         tcp_verify_left_out(tp);
2099
2100         /* Too bad if TCP was application limited */
2101         tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2102
2103         /* Earlier loss recovery underway (see RFC4138; Appendix B).
2104          * The last condition is necessary at least in tp->frto_counter case.
2105          */
2106         if (tcp_is_sackfrto(tp) && (tp->frto_counter ||
2107             ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
2108             after(tp->high_seq, tp->snd_una)) {
2109                 tp->frto_highmark = tp->high_seq;
2110         } else {
2111                 tp->frto_highmark = tp->snd_nxt;
2112         }
2113         tcp_set_ca_state(sk, TCP_CA_Disorder);
2114         tp->high_seq = tp->snd_nxt;
2115         tp->frto_counter = 1;
2116 }
2117
2118 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
2119  * which indicates that we should follow the traditional RTO recovery,
2120  * i.e. mark everything lost and do go-back-N retransmission.
2121  */
2122 static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
2123 {
2124         struct tcp_sock *tp = tcp_sk(sk);
2125         struct sk_buff *skb;
2126
2127         tp->lost_out = 0;
2128         tp->retrans_out = 0;
2129         if (tcp_is_reno(tp))
2130                 tcp_reset_reno_sack(tp);
2131
2132         tcp_for_write_queue(skb, sk) {
2133                 if (skb == tcp_send_head(sk))
2134                         break;
2135
2136                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2137                 /*
2138                  * Count the retransmission made on RTO correctly (only when
2139                  * waiting for the first ACK and did not get it)...
2140                  */
2141                 if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) {
2142                         /* For some reason this R-bit might get cleared? */
2143                         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
2144                                 tp->retrans_out += tcp_skb_pcount(skb);
2145                         /* ...enter this if branch just for the first segment */
2146                         flag |= FLAG_DATA_ACKED;
2147                 } else {
2148                         if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2149                                 tp->undo_marker = 0;
2150                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2151                 }
2152
2153                 /* Marking forward transmissions that were made after RTO lost
2154                  * can cause unnecessary retransmissions in some scenarios,
2155                  * SACK blocks will mitigate that in some but not in all cases.
2156                  * We used to not mark them but it was causing break-ups with
2157                  * receivers that do only in-order receival.
2158                  *
2159                  * TODO: we could detect presence of such receiver and select
2160                  * different behavior per flow.
2161                  */
2162                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2163                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2164                         tp->lost_out += tcp_skb_pcount(skb);
2165                         tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2166                 }
2167         }
2168         tcp_verify_left_out(tp);
2169
2170         tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
2171         tp->snd_cwnd_cnt = 0;
2172         tp->snd_cwnd_stamp = tcp_time_stamp;
2173         tp->frto_counter = 0;
2174         tp->bytes_acked = 0;
2175
2176         tp->reordering = min_t(unsigned int, tp->reordering,
2177                                sysctl_tcp_reordering);
2178         tcp_set_ca_state(sk, TCP_CA_Loss);
2179         tp->high_seq = tp->snd_nxt;
2180         TCP_ECN_queue_cwr(tp);
2181
2182         tcp_clear_all_retrans_hints(tp);
2183 }
2184
2185 static void tcp_clear_retrans_partial(struct tcp_sock *tp)
2186 {
2187         tp->retrans_out = 0;
2188         tp->lost_out = 0;
2189
2190         tp->undo_marker = 0;
2191         tp->undo_retrans = 0;
2192 }
2193
2194 void tcp_clear_retrans(struct tcp_sock *tp)
2195 {
2196         tcp_clear_retrans_partial(tp);
2197
2198         tp->fackets_out = 0;
2199         tp->sacked_out = 0;
2200 }
2201
2202 /* Enter Loss state. If "how" is not zero, forget all SACK information
2203  * and reset tags completely, otherwise preserve SACKs. If receiver
2204  * dropped its ofo queue, we will know this due to reneging detection.
2205  */
2206 void tcp_enter_loss(struct sock *sk, int how)
2207 {
2208         const struct inet_connection_sock *icsk = inet_csk(sk);
2209         struct tcp_sock *tp = tcp_sk(sk);
2210         struct sk_buff *skb;
2211
2212         /* Reduce ssthresh if it has not yet been made inside this window. */
2213         if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
2214             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
2215                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2216                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2217                 tcp_ca_event(sk, CA_EVENT_LOSS);
2218         }
2219         tp->snd_cwnd       = 1;
2220         tp->snd_cwnd_cnt   = 0;
2221         tp->snd_cwnd_stamp = tcp_time_stamp;
2222
2223         tp->bytes_acked = 0;
2224         tcp_clear_retrans_partial(tp);
2225
2226         if (tcp_is_reno(tp))
2227                 tcp_reset_reno_sack(tp);
2228
2229         if (!how) {
2230                 /* Push undo marker, if it was plain RTO and nothing
2231                  * was retransmitted. */
2232                 tp->undo_marker = tp->snd_una;
2233         } else {
2234                 tp->sacked_out = 0;
2235                 tp->fackets_out = 0;
2236         }
2237         tcp_clear_all_retrans_hints(tp);
2238
2239         tcp_for_write_queue(skb, sk) {
2240                 if (skb == tcp_send_head(sk))
2241                         break;
2242
2243                 if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2244                         tp->undo_marker = 0;
2245                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
2246                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
2247                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
2248                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2249                         tp->lost_out += tcp_skb_pcount(skb);
2250                         tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2251                 }
2252         }
2253         tcp_verify_left_out(tp);
2254
2255         tp->reordering = min_t(unsigned int, tp->reordering,
2256                                sysctl_tcp_reordering);
2257         tcp_set_ca_state(sk, TCP_CA_Loss);
2258         tp->high_seq = tp->snd_nxt;
2259         TCP_ECN_queue_cwr(tp);
2260         /* Abort F-RTO algorithm if one is in progress */
2261         tp->frto_counter = 0;
2262 }
2263
2264 /* If ACK arrived pointing to a remembered SACK, it means that our
2265  * remembered SACKs do not reflect real state of receiver i.e.
2266  * receiver _host_ is heavily congested (or buggy).
2267  *
2268  * Do processing similar to RTO timeout.
2269  */
2270 static int tcp_check_sack_reneging(struct sock *sk, int flag)
2271 {
2272         if (flag & FLAG_SACK_RENEGING) {
2273                 struct inet_connection_sock *icsk = inet_csk(sk);
2274                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
2275
2276                 tcp_enter_loss(sk, 1);
2277                 icsk->icsk_retransmits++;
2278                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
2279                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2280                                           icsk->icsk_rto, TCP_RTO_MAX);
2281                 return 1;
2282         }
2283         return 0;
2284 }
2285
2286 static inline int tcp_fackets_out(struct tcp_sock *tp)
2287 {
2288         return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
2289 }
2290
2291 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2292  * counter when SACK is enabled (without SACK, sacked_out is used for
2293  * that purpose).
2294  *
2295  * Instead, with FACK TCP uses fackets_out that includes both SACKed
2296  * segments up to the highest received SACK block so far and holes in
2297  * between them.
2298  *
2299  * With reordering, holes may still be in flight, so RFC3517 recovery
2300  * uses pure sacked_out (total number of SACKed segments) even though
2301  * it violates the RFC that uses duplicate ACKs, often these are equal
2302  * but when e.g. out-of-window ACKs or packet duplication occurs,
2303  * they differ. Since neither occurs due to loss, TCP should really
2304  * ignore them.
2305  */
2306 static inline int tcp_dupack_heurestics(struct tcp_sock *tp)
2307 {
2308         return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
2309 }
2310
2311 static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
2312 {
2313         return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
2314 }
2315
2316 static inline int tcp_head_timedout(struct sock *sk)
2317 {
2318         struct tcp_sock *tp = tcp_sk(sk);
2319
2320         return tp->packets_out &&
2321                tcp_skb_timedout(sk, tcp_write_queue_head(sk));
2322 }
2323
2324 /* Linux NewReno/SACK/FACK/ECN state machine.
2325  * --------------------------------------
2326  *
2327  * "Open"       Normal state, no dubious events, fast path.
2328  * "Disorder"   In all the respects it is "Open",
2329  *              but requires a bit more attention. It is entered when
2330  *              we see some SACKs or dupacks. It is split of "Open"
2331  *              mainly to move some processing from fast path to slow one.
2332  * "CWR"        CWND was reduced due to some Congestion Notification event.
2333  *              It can be ECN, ICMP source quench, local device congestion.
2334  * "Recovery"   CWND was reduced, we are fast-retransmitting.
2335  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
2336  *
2337  * tcp_fastretrans_alert() is entered:
2338  * - each incoming ACK, if state is not "Open"
2339  * - when arrived ACK is unusual, namely:
2340  *      * SACK
2341  *      * Duplicate ACK.
2342  *      * ECN ECE.
2343  *
2344  * Counting packets in flight is pretty simple.
2345  *
2346  *      in_flight = packets_out - left_out + retrans_out
2347  *
2348  *      packets_out is SND.NXT-SND.UNA counted in packets.
2349  *
2350  *      retrans_out is number of retransmitted segments.
2351  *
2352  *      left_out is number of segments left network, but not ACKed yet.
2353  *
2354  *              left_out = sacked_out + lost_out
2355  *
2356  *     sacked_out: Packets, which arrived to receiver out of order
2357  *                 and hence not ACKed. With SACKs this number is simply
2358  *                 amount of SACKed data. Even without SACKs
2359  *                 it is easy to give pretty reliable estimate of this number,
2360  *                 counting duplicate ACKs.
2361  *
2362  *       lost_out: Packets lost by network. TCP has no explicit
2363  *                 "loss notification" feedback from network (for now).
2364  *                 It means that this number can be only _guessed_.
2365  *                 Actually, it is the heuristics to predict lossage that
2366  *                 distinguishes different algorithms.
2367  *
2368  *      F.e. after RTO, when all the queue is considered as lost,
2369  *      lost_out = packets_out and in_flight = retrans_out.
2370  *
2371  *              Essentially, we have now two algorithms counting
2372  *              lost packets.
2373  *
2374  *              FACK: It is the simplest heuristics. As soon as we decided
2375  *              that something is lost, we decide that _all_ not SACKed
2376  *              packets until the most forward SACK are lost. I.e.
2377  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
2378  *              It is absolutely correct estimate, if network does not reorder
2379  *              packets. And it loses any connection to reality when reordering
2380  *              takes place. We use FACK by default until reordering
2381  *              is suspected on the path to this destination.
2382  *
2383  *              NewReno: when Recovery is entered, we assume that one segment
2384  *              is lost (classic Reno). While we are in Recovery and
2385  *              a partial ACK arrives, we assume that one more packet
2386  *              is lost (NewReno). This heuristics are the same in NewReno
2387  *              and SACK.
2388  *
2389  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
2390  *  deflation etc. CWND is real congestion window, never inflated, changes
2391  *  only according to classic VJ rules.
2392  *
2393  * Really tricky (and requiring careful tuning) part of algorithm
2394  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2395  * The first determines the moment _when_ we should reduce CWND and,
2396  * hence, slow down forward transmission. In fact, it determines the moment
2397  * when we decide that hole is caused by loss, rather than by a reorder.
2398  *
2399  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2400  * holes, caused by lost packets.
2401  *
2402  * And the most logically complicated part of algorithm is undo
2403  * heuristics. We detect false retransmits due to both too early
2404  * fast retransmit (reordering) and underestimated RTO, analyzing
2405  * timestamps and D-SACKs. When we detect that some segments were
2406  * retransmitted by mistake and CWND reduction was wrong, we undo
2407  * window reduction and abort recovery phase. This logic is hidden
2408  * inside several functions named tcp_try_undo_<something>.
2409  */
2410
2411 /* This function decides, when we should leave Disordered state
2412  * and enter Recovery phase, reducing congestion window.
2413  *
2414  * Main question: may we further continue forward transmission
2415  * with the same cwnd?
2416  */
2417 static int tcp_time_to_recover(struct sock *sk)
2418 {
2419         struct tcp_sock *tp = tcp_sk(sk);
2420         __u32 packets_out;
2421
2422         /* Do not perform any recovery during F-RTO algorithm */
2423         if (tp->frto_counter)
2424                 return 0;
2425
2426         /* Trick#1: The loss is proven. */
2427         if (tp->lost_out)
2428                 return 1;
2429
2430         /* Not-A-Trick#2 : Classic rule... */
2431         if (tcp_dupack_heurestics(tp) > tp->reordering)
2432                 return 1;
2433
2434         /* Trick#3 : when we use RFC2988 timer restart, fast
2435          * retransmit can be triggered by timeout of queue head.
2436          */
2437         if (tcp_is_fack(tp) && tcp_head_timedout(sk))
2438                 return 1;
2439
2440         /* Trick#4: It is still not OK... But will it be useful to delay
2441          * recovery more?
2442          */
2443         packets_out = tp->packets_out;
2444         if (packets_out <= tp->reordering &&
2445             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
2446             !tcp_may_send_now(sk)) {
2447                 /* We have nothing to send. This connection is limited
2448                  * either by receiver window or by application.
2449                  */
2450                 return 1;
2451         }
2452
2453         return 0;
2454 }
2455
2456 /* Mark head of queue up as lost. With RFC3517 SACK, the packets is
2457  * is against sacked "cnt", otherwise it's against facked "cnt"
2458  */
2459 static void tcp_mark_head_lost(struct sock *sk, int packets)
2460 {
2461         struct tcp_sock *tp = tcp_sk(sk);
2462         struct sk_buff *skb;
2463         int cnt, oldcnt;
2464         int err;
2465         unsigned int mss;
2466
2467         WARN_ON(packets > tp->packets_out);
2468         if (tp->lost_skb_hint) {
2469                 skb = tp->lost_skb_hint;
2470                 cnt = tp->lost_cnt_hint;
2471         } else {
2472                 skb = tcp_write_queue_head(sk);
2473                 cnt = 0;
2474         }
2475
2476         tcp_for_write_queue_from(skb, sk) {
2477                 if (skb == tcp_send_head(sk))
2478                         break;
2479                 /* TODO: do this better */
2480                 /* this is not the most efficient way to do this... */
2481                 tp->lost_skb_hint = skb;
2482                 tp->lost_cnt_hint = cnt;
2483
2484                 if (after(TCP_SKB_CB(skb)->end_seq, tp->high_seq))
2485                         break;
2486
2487                 oldcnt = cnt;
2488                 if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2489                     (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2490                         cnt += tcp_skb_pcount(skb);
2491
2492                 if (cnt > packets) {
2493                         if (tcp_is_sack(tp) || (oldcnt >= packets))
2494                                 break;
2495
2496                         mss = skb_shinfo(skb)->gso_size;
2497                         err = tcp_fragment(sk, skb, (packets - oldcnt) * mss, mss);
2498                         if (err < 0)
2499                                 break;
2500                         cnt = packets;
2501                 }
2502
2503                 tcp_skb_mark_lost(tp, skb);
2504         }
2505         tcp_verify_left_out(tp);
2506 }
2507
2508 /* Account newly detected lost packet(s) */
2509
2510 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2511 {
2512         struct tcp_sock *tp = tcp_sk(sk);
2513
2514         if (tcp_is_reno(tp)) {
2515                 tcp_mark_head_lost(sk, 1);
2516         } else if (tcp_is_fack(tp)) {
2517                 int lost = tp->fackets_out - tp->reordering;
2518                 if (lost <= 0)
2519                         lost = 1;
2520                 tcp_mark_head_lost(sk, lost);
2521         } else {
2522                 int sacked_upto = tp->sacked_out - tp->reordering;
2523                 if (sacked_upto < fast_rexmit)
2524                         sacked_upto = fast_rexmit;
2525                 tcp_mark_head_lost(sk, sacked_upto);
2526         }
2527
2528         /* New heuristics: it is possible only after we switched
2529          * to restart timer each time when something is ACKed.
2530          * Hence, we can detect timed out packets during fast
2531          * retransmit without falling to slow start.
2532          */
2533         if (tcp_is_fack(tp) && tcp_head_timedout(sk)) {
2534                 struct sk_buff *skb;
2535
2536                 skb = tp->scoreboard_skb_hint ? tp->scoreboard_skb_hint
2537                         : tcp_write_queue_head(sk);
2538
2539                 tcp_for_write_queue_from(skb, sk) {
2540                         if (skb == tcp_send_head(sk))
2541                                 break;
2542                         if (!tcp_skb_timedout(sk, skb))
2543                                 break;
2544
2545                         tcp_skb_mark_lost(tp, skb);
2546                 }
2547
2548                 tp->scoreboard_skb_hint = skb;
2549
2550                 tcp_verify_left_out(tp);
2551         }
2552 }
2553
2554 /* CWND moderation, preventing bursts due to too big ACKs
2555  * in dubious situations.
2556  */
2557 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2558 {
2559         tp->snd_cwnd = min(tp->snd_cwnd,
2560                            tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2561         tp->snd_cwnd_stamp = tcp_time_stamp;
2562 }
2563
2564 /* Lower bound on congestion window is slow start threshold
2565  * unless congestion avoidance choice decides to overide it.
2566  */
2567 static inline u32 tcp_cwnd_min(const struct sock *sk)
2568 {
2569         const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
2570
2571         return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
2572 }
2573
2574 /* Decrease cwnd each second ack. */
2575 static void tcp_cwnd_down(struct sock *sk, int flag)
2576 {
2577         struct tcp_sock *tp = tcp_sk(sk);
2578         int decr = tp->snd_cwnd_cnt + 1;
2579
2580         if ((flag & (FLAG_ANY_PROGRESS | FLAG_DSACKING_ACK)) ||
2581             (tcp_is_reno(tp) && !(flag & FLAG_NOT_DUP))) {
2582                 tp->snd_cwnd_cnt = decr & 1;
2583                 decr >>= 1;
2584
2585                 if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
2586                         tp->snd_cwnd -= decr;
2587
2588                 tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2589                 tp->snd_cwnd_stamp = tcp_time_stamp;
2590         }
2591 }
2592
2593 /* Nothing was retransmitted or returned timestamp is less
2594  * than timestamp of the first retransmission.
2595  */
2596 static inline int tcp_packet_delayed(struct tcp_sock *tp)
2597 {
2598         return !tp->retrans_stamp ||
2599                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2600                  before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp));
2601 }
2602
2603 /* Undo procedures. */
2604
2605 #if FASTRETRANS_DEBUG > 1
2606 static void DBGUNDO(struct sock *sk, const char *msg)
2607 {
2608         struct tcp_sock *tp = tcp_sk(sk);
2609         struct inet_sock *inet = inet_sk(sk);
2610
2611         if (sk->sk_family == AF_INET) {
2612                 printk(KERN_DEBUG "Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2613                        msg,
2614                        &inet->daddr, ntohs(inet->dport),
2615                        tp->snd_cwnd, tcp_left_out(tp),
2616                        tp->snd_ssthresh, tp->prior_ssthresh,
2617                        tp->packets_out);
2618         }
2619 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
2620         else if (sk->sk_family == AF_INET6) {
2621                 struct ipv6_pinfo *np = inet6_sk(sk);
2622                 printk(KERN_DEBUG "Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2623                        msg,
2624                        &np->daddr, ntohs(inet->dport),
2625                        tp->snd_cwnd, tcp_left_out(tp),
2626                        tp->snd_ssthresh, tp->prior_ssthresh,
2627                        tp->packets_out);
2628         }
2629 #endif
2630 }
2631 #else
2632 #define DBGUNDO(x...) do { } while (0)
2633 #endif
2634
2635 static void tcp_undo_cwr(struct sock *sk, const int undo)
2636 {
2637         struct tcp_sock *tp = tcp_sk(sk);
2638
2639         if (tp->prior_ssthresh) {
2640                 const struct inet_connection_sock *icsk = inet_csk(sk);
2641
2642                 if (icsk->icsk_ca_ops->undo_cwnd)
2643                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2644                 else
2645                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2646
2647                 if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
2648                         tp->snd_ssthresh = tp->prior_ssthresh;
2649                         TCP_ECN_withdraw_cwr(tp);
2650                 }
2651         } else {
2652                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2653         }
2654         tcp_moderate_cwnd(tp);
2655         tp->snd_cwnd_stamp = tcp_time_stamp;
2656 }
2657
2658 static inline int tcp_may_undo(struct tcp_sock *tp)
2659 {
2660         return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2661 }
2662
2663 /* People celebrate: "We love our President!" */
2664 static int tcp_try_undo_recovery(struct sock *sk)
2665 {
2666         struct tcp_sock *tp = tcp_sk(sk);
2667
2668         if (tcp_may_undo(tp)) {
2669                 int mib_idx;
2670
2671                 /* Happy end! We did not retransmit anything
2672                  * or our original transmission succeeded.
2673                  */
2674                 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2675                 tcp_undo_cwr(sk, 1);
2676                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2677                         mib_idx = LINUX_MIB_TCPLOSSUNDO;
2678                 else
2679                         mib_idx = LINUX_MIB_TCPFULLUNDO;
2680
2681                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2682                 tp->undo_marker = 0;
2683         }
2684         if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2685                 /* Hold old state until something *above* high_seq
2686                  * is ACKed. For Reno it is MUST to prevent false
2687                  * fast retransmits (RFC2582). SACK TCP is safe. */
2688                 tcp_moderate_cwnd(tp);
2689                 return 1;
2690         }
2691         tcp_set_ca_state(sk, TCP_CA_Open);
2692         return 0;
2693 }
2694
2695 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2696 static void tcp_try_undo_dsack(struct sock *sk)
2697 {
2698         struct tcp_sock *tp = tcp_sk(sk);
2699
2700         if (tp->undo_marker && !tp->undo_retrans) {
2701                 DBGUNDO(sk, "D-SACK");
2702                 tcp_undo_cwr(sk, 1);
2703                 tp->undo_marker = 0;
2704                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2705         }
2706 }
2707
2708 /* Undo during fast recovery after partial ACK. */
2709
2710 static int tcp_try_undo_partial(struct sock *sk, int acked)
2711 {
2712         struct tcp_sock *tp = tcp_sk(sk);
2713         /* Partial ACK arrived. Force Hoe's retransmit. */
2714         int failed = tcp_is_reno(tp) || (tcp_fackets_out(tp) > tp->reordering);
2715
2716         if (tcp_may_undo(tp)) {
2717                 /* Plain luck! Hole if filled with delayed
2718                  * packet, rather than with a retransmit.
2719                  */
2720                 if (tp->retrans_out == 0)
2721                         tp->retrans_stamp = 0;
2722
2723                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2724
2725                 DBGUNDO(sk, "Hoe");
2726                 tcp_undo_cwr(sk, 0);
2727                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2728
2729                 /* So... Do not make Hoe's retransmit yet.
2730                  * If the first packet was delayed, the rest
2731                  * ones are most probably delayed as well.
2732                  */
2733                 failed = 0;
2734         }
2735         return failed;
2736 }
2737
2738 /* Undo during loss recovery after partial ACK. */
2739 static int tcp_try_undo_loss(struct sock *sk)
2740 {
2741         struct tcp_sock *tp = tcp_sk(sk);
2742
2743         if (tcp_may_undo(tp)) {
2744                 struct sk_buff *skb;
2745                 tcp_for_write_queue(skb, sk) {
2746                         if (skb == tcp_send_head(sk))
2747                                 break;
2748                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2749                 }
2750
2751                 tcp_clear_all_retrans_hints(tp);
2752
2753                 DBGUNDO(sk, "partial loss");
2754                 tp->lost_out = 0;
2755                 tcp_undo_cwr(sk, 1);
2756                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2757                 inet_csk(sk)->icsk_retransmits = 0;
2758                 tp->undo_marker = 0;
2759                 if (tcp_is_sack(tp))
2760                         tcp_set_ca_state(sk, TCP_CA_Open);
2761                 return 1;
2762         }
2763         return 0;
2764 }
2765
2766 static inline void tcp_complete_cwr(struct sock *sk)
2767 {
2768         struct tcp_sock *tp = tcp_sk(sk);
2769         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2770         tp->snd_cwnd_stamp = tcp_time_stamp;
2771         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2772 }
2773
2774 static void tcp_try_keep_open(struct sock *sk)
2775 {
2776         struct tcp_sock *tp = tcp_sk(sk);
2777         int state = TCP_CA_Open;
2778
2779         if (tcp_left_out(tp) || tp->retrans_out || tp->undo_marker)
2780                 state = TCP_CA_Disorder;
2781
2782         if (inet_csk(sk)->icsk_ca_state != state) {
2783                 tcp_set_ca_state(sk, state);
2784                 tp->high_seq = tp->snd_nxt;
2785         }
2786 }
2787
2788 static void tcp_try_to_open(struct sock *sk, int flag)
2789 {
2790         struct tcp_sock *tp = tcp_sk(sk);
2791
2792         tcp_verify_left_out(tp);
2793
2794         if (!tp->frto_counter && tp->retrans_out == 0)
2795                 tp->retrans_stamp = 0;
2796
2797         if (flag & FLAG_ECE)
2798                 tcp_enter_cwr(sk, 1);
2799
2800         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2801                 tcp_try_keep_open(sk);
2802                 tcp_moderate_cwnd(tp);
2803         } else {
2804                 tcp_cwnd_down(sk, flag);
2805         }
2806 }
2807
2808 static void tcp_mtup_probe_failed(struct sock *sk)
2809 {
2810         struct inet_connection_sock *icsk = inet_csk(sk);
2811
2812         icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2813         icsk->icsk_mtup.probe_size = 0;
2814 }
2815
2816 static void tcp_mtup_probe_success(struct sock *sk, struct sk_buff *skb)
2817 {
2818         struct tcp_sock *tp = tcp_sk(sk);
2819         struct inet_connection_sock *icsk = inet_csk(sk);
2820
2821         /* FIXME: breaks with very large cwnd */
2822         tp->prior_ssthresh = tcp_current_ssthresh(sk);
2823         tp->snd_cwnd = tp->snd_cwnd *
2824                        tcp_mss_to_mtu(sk, tp->mss_cache) /
2825                        icsk->icsk_mtup.probe_size;
2826         tp->snd_cwnd_cnt = 0;
2827         tp->snd_cwnd_stamp = tcp_time_stamp;
2828         tp->rcv_ssthresh = tcp_current_ssthresh(sk);
2829
2830         icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2831         icsk->icsk_mtup.probe_size = 0;
2832         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2833 }
2834
2835 /* Do a simple retransmit without using the backoff mechanisms in
2836  * tcp_timer. This is used for path mtu discovery.
2837  * The socket is already locked here.
2838  */
2839 void tcp_simple_retransmit(struct sock *sk)
2840 {
2841         const struct inet_connection_sock *icsk = inet_csk(sk);
2842         struct tcp_sock *tp = tcp_sk(sk);
2843         struct sk_buff *skb;
2844         unsigned int mss = tcp_current_mss(sk, 0);
2845         u32 prior_lost = tp->lost_out;
2846
2847         tcp_for_write_queue(skb, sk) {
2848                 if (skb == tcp_send_head(sk))
2849                         break;
2850                 if (tcp_skb_seglen(skb) > mss &&
2851                     !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2852                         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2853                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2854                                 tp->retrans_out -= tcp_skb_pcount(skb);
2855                         }
2856                         tcp_skb_mark_lost_uncond_verify(tp, skb);
2857                 }
2858         }
2859
2860         tcp_clear_retrans_hints_partial(tp);
2861
2862         if (prior_lost == tp->lost_out)
2863                 return;
2864
2865         if (tcp_is_reno(tp))
2866                 tcp_limit_reno_sacked(tp);
2867
2868         tcp_verify_left_out(tp);
2869
2870         /* Don't muck with the congestion window here.
2871          * Reason is that we do not increase amount of _data_
2872          * in network, but units changed and effective
2873          * cwnd/ssthresh really reduced now.
2874          */
2875         if (icsk->icsk_ca_state != TCP_CA_Loss) {
2876                 tp->high_seq = tp->snd_nxt;
2877                 tp->snd_ssthresh = tcp_current_ssthresh(sk);
2878                 tp->prior_ssthresh = 0;
2879                 tp->undo_marker = 0;
2880                 tcp_set_ca_state(sk, TCP_CA_Loss);
2881         }
2882         tcp_xmit_retransmit_queue(sk);
2883 }
2884
2885 /* Process an event, which can update packets-in-flight not trivially.
2886  * Main goal of this function is to calculate new estimate for left_out,
2887  * taking into account both packets sitting in receiver's buffer and
2888  * packets lost by network.
2889  *
2890  * Besides that it does CWND reduction, when packet loss is detected
2891  * and changes state of machine.
2892  *
2893  * It does _not_ decide what to send, it is made in function
2894  * tcp_xmit_retransmit_queue().
2895  */
2896 static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, int flag)
2897 {
2898         struct inet_connection_sock *icsk = inet_csk(sk);
2899         struct tcp_sock *tp = tcp_sk(sk);
2900         int is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
2901         int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
2902                                     (tcp_fackets_out(tp) > tp->reordering));
2903         int fast_rexmit = 0, mib_idx;
2904
2905         if (WARN_ON(!tp->packets_out && tp->sacked_out))
2906                 tp->sacked_out = 0;
2907         if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2908                 tp->fackets_out = 0;
2909
2910         /* Now state machine starts.
2911          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2912         if (flag & FLAG_ECE)
2913                 tp->prior_ssthresh = 0;
2914
2915         /* B. In all the states check for reneging SACKs. */
2916         if (tcp_check_sack_reneging(sk, flag))
2917                 return;
2918
2919         /* C. Process data loss notification, provided it is valid. */
2920         if (tcp_is_fack(tp) && (flag & FLAG_DATA_LOST) &&
2921             before(tp->snd_una, tp->high_seq) &&
2922             icsk->icsk_ca_state != TCP_CA_Open &&
2923             tp->fackets_out > tp->reordering) {
2924                 tcp_mark_head_lost(sk, tp->fackets_out - tp->reordering);
2925                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSS);
2926         }
2927
2928         /* D. Check consistency of the current state. */
2929         tcp_verify_left_out(tp);
2930
2931         /* E. Check state exit conditions. State can be terminated
2932          *    when high_seq is ACKed. */
2933         if (icsk->icsk_ca_state == TCP_CA_Open) {
2934                 WARN_ON(tp->retrans_out != 0);
2935                 tp->retrans_stamp = 0;
2936         } else if (!before(tp->snd_una, tp->high_seq)) {
2937                 switch (icsk->icsk_ca_state) {
2938                 case TCP_CA_Loss:
2939                         icsk->icsk_retransmits = 0;
2940                         if (tcp_try_undo_recovery(sk))
2941                                 return;
2942                         break;
2943
2944                 case TCP_CA_CWR:
2945                         /* CWR is to be held something *above* high_seq
2946                          * is ACKed for CWR bit to reach receiver. */
2947                         if (tp->snd_una != tp->high_seq) {
2948                                 tcp_complete_cwr(sk);
2949                                 tcp_set_ca_state(sk, TCP_CA_Open);
2950                         }
2951                         break;
2952
2953                 case TCP_CA_Disorder:
2954                         tcp_try_undo_dsack(sk);
2955                         if (!tp->undo_marker ||
2956                             /* For SACK case do not Open to allow to undo
2957                              * catching for all duplicate ACKs. */
2958                             tcp_is_reno(tp) || tp->snd_una != tp->high_seq) {
2959                                 tp->undo_marker = 0;
2960                                 tcp_set_ca_state(sk, TCP_CA_Open);
2961                         }
2962                         break;
2963
2964                 case TCP_CA_Recovery:
2965                         if (tcp_is_reno(tp))
2966                                 tcp_reset_reno_sack(tp);
2967                         if (tcp_try_undo_recovery(sk))
2968                                 return;
2969                         tcp_complete_cwr(sk);
2970                         break;
2971                 }
2972         }
2973
2974         /* F. Process state. */
2975         switch (icsk->icsk_ca_state) {
2976         case TCP_CA_Recovery:
2977                 if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2978                         if (tcp_is_reno(tp) && is_dupack)
2979                                 tcp_add_reno_sack(sk);
2980                 } else
2981                         do_lost = tcp_try_undo_partial(sk, pkts_acked);
2982                 break;
2983         case TCP_CA_Loss:
2984                 if (flag & FLAG_DATA_ACKED)
2985                         icsk->icsk_retransmits = 0;
2986                 if (tcp_is_reno(tp) && flag & FLAG_SND_UNA_ADVANCED)
2987                         tcp_reset_reno_sack(tp);
2988                 if (!tcp_try_undo_loss(sk)) {
2989                         tcp_moderate_cwnd(tp);
2990                         tcp_xmit_retransmit_queue(sk);
2991                         return;
2992                 }
2993                 if (icsk->icsk_ca_state != TCP_CA_Open)
2994                         return;
2995                 /* Loss is undone; fall through to processing in Open state. */
2996         default:
2997                 if (tcp_is_reno(tp)) {
2998                         if (flag & FLAG_SND_UNA_ADVANCED)
2999                                 tcp_reset_reno_sack(tp);
3000                         if (is_dupack)
3001                                 tcp_add_reno_sack(sk);
3002                 }
3003
3004                 if (icsk->icsk_ca_state == TCP_CA_Disorder)
3005                         tcp_try_undo_dsack(sk);
3006
3007                 if (!tcp_time_to_recover(sk)) {
3008                         tcp_try_to_open(sk, flag);
3009                         return;
3010                 }
3011
3012                 /* MTU probe failure: don't reduce cwnd */
3013                 if (icsk->icsk_ca_state < TCP_CA_CWR &&
3014                     icsk->icsk_mtup.probe_size &&
3015                     tp->snd_una == tp->mtu_probe.probe_seq_start) {
3016                         tcp_mtup_probe_failed(sk);
3017                         /* Restores the reduction we did in tcp_mtup_probe() */
3018                         tp->snd_cwnd++;
3019                         tcp_simple_retransmit(sk);
3020                         return;
3021                 }
3022
3023                 /* Otherwise enter Recovery state */
3024
3025                 if (tcp_is_reno(tp))
3026                         mib_idx = LINUX_MIB_TCPRENORECOVERY;
3027                 else
3028                         mib_idx = LINUX_MIB_TCPSACKRECOVERY;
3029
3030                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
3031
3032                 tp->high_seq = tp->snd_nxt;
3033                 tp->prior_ssthresh = 0;
3034                 tp->undo_marker = tp->snd_una;
3035                 tp->undo_retrans = tp->retrans_out;
3036
3037                 if (icsk->icsk_ca_state < TCP_CA_CWR) {
3038                         if (!(flag & FLAG_ECE))
3039                                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
3040                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
3041                         TCP_ECN_queue_cwr(tp);
3042                 }
3043
3044                 tp->bytes_acked = 0;
3045                 tp->snd_cwnd_cnt = 0;
3046                 tcp_set_ca_state(sk, TCP_CA_Recovery);
3047                 fast_rexmit = 1;
3048         }
3049
3050         if (do_lost || (tcp_is_fack(tp) && tcp_head_timedout(sk)))
3051                 tcp_update_scoreboard(sk, fast_rexmit);
3052         tcp_cwnd_down(sk, flag);
3053         tcp_xmit_retransmit_queue(sk);
3054 }
3055
3056 static void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt)
3057 {
3058         tcp_rtt_estimator(sk, seq_rtt);
3059         tcp_set_rto(sk);
3060         inet_csk(sk)->icsk_backoff = 0;
3061 }
3062
3063 /* Read draft-ietf-tcplw-high-performance before mucking
3064  * with this code. (Supersedes RFC1323)
3065  */
3066 static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
3067 {
3068         /* RTTM Rule: A TSecr value received in a segment is used to
3069          * update the averaged RTT measurement only if the segment
3070          * acknowledges some new data, i.e., only if it advances the
3071          * left edge of the send window.
3072          *
3073          * See draft-ietf-tcplw-high-performance-00, section 3.3.
3074          * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
3075          *
3076          * Changed: reset backoff as soon as we see the first valid sample.
3077          * If we do not, we get strongly overestimated rto. With timestamps
3078          * samples are accepted even from very old segments: f.e., when rtt=1
3079          * increases to 8, we retransmit 5 times and after 8 seconds delayed
3080          * answer arrives rto becomes 120 seconds! If at least one of segments
3081          * in window is lost... Voila.                          --ANK (010210)
3082          */
3083         struct tcp_sock *tp = tcp_sk(sk);
3084
3085         tcp_valid_rtt_meas(sk, tcp_time_stamp - tp->rx_opt.rcv_tsecr);
3086 }
3087
3088 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
3089 {
3090         /* We don't have a timestamp. Can only use
3091          * packets that are not retransmitted to determine
3092          * rtt estimates. Also, we must not reset the
3093          * backoff for rto until we get a non-retransmitted
3094          * packet. This allows us to deal with a situation
3095          * where the network delay has increased suddenly.
3096          * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
3097          */
3098
3099         if (flag & FLAG_RETRANS_DATA_ACKED)
3100                 return;
3101
3102         tcp_valid_rtt_meas(sk, seq_rtt);
3103 }
3104
3105 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
3106                                       const s32 seq_rtt)
3107 {
3108         const struct tcp_sock *tp = tcp_sk(sk);
3109         /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
3110         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3111                 tcp_ack_saw_tstamp(sk, flag);
3112         else if (seq_rtt >= 0)
3113                 tcp_ack_no_tstamp(sk, seq_rtt, flag);
3114 }
3115
3116 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
3117 {
3118         const struct inet_connection_sock *icsk = inet_csk(sk);
3119         icsk->icsk_ca_ops->cong_avoid(sk, ack, in_flight);
3120         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
3121 }
3122
3123 /* Restart timer after forward progress on connection.
3124  * RFC2988 recommends to restart timer to now+rto.
3125  */
3126 static void tcp_rearm_rto(struct sock *sk)
3127 {
3128         struct tcp_sock *tp = tcp_sk(sk);
3129
3130         if (!tp->packets_out) {
3131                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3132         } else {
3133                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3134                                           inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3135         }
3136 }
3137
3138 /* If we get here, the whole TSO packet has not been acked. */
3139 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3140 {
3141         struct tcp_sock *tp = tcp_sk(sk);
3142         u32 packets_acked;
3143
3144         BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3145
3146         packets_acked = tcp_skb_pcount(skb);
3147         if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3148                 return 0;
3149         packets_acked -= tcp_skb_pcount(skb);
3150
3151         if (packets_acked) {
3152                 BUG_ON(tcp_skb_pcount(skb) == 0);
3153                 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3154         }
3155
3156         return packets_acked;
3157 }
3158
3159 /* Remove acknowledged frames from the retransmission queue. If our packet
3160  * is before the ack sequence we can discard it as it's confirmed to have
3161  * arrived at the other end.
3162  */
3163 static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3164                                u32 prior_snd_una)
3165 {
3166         struct tcp_sock *tp = tcp_sk(sk);
3167         const struct inet_connection_sock *icsk = inet_csk(sk);
3168         struct sk_buff *skb;
3169         u32 now = tcp_time_stamp;
3170         int fully_acked = 1;
3171         int flag = 0;
3172         u32 pkts_acked = 0;
3173         u32 reord = tp->packets_out;
3174         u32 prior_sacked = tp->sacked_out;
3175         s32 seq_rtt = -1;
3176         s32 ca_seq_rtt = -1;
3177         ktime_t last_ackt = net_invalid_timestamp();
3178
3179         while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3180                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3181                 u32 end_seq;
3182                 u32 acked_pcount;
3183                 u8 sacked = scb->sacked;
3184
3185                 /* Determine how many packets and what bytes were acked, tso and else */
3186                 if (after(scb->end_seq, tp->snd_una)) {
3187                         if (tcp_skb_pcount(skb) == 1 ||
3188                             !after(tp->snd_una, scb->seq))
3189                                 break;
3190
3191                         acked_pcount = tcp_tso_acked(sk, skb);
3192                         if (!acked_pcount)
3193                                 break;
3194
3195                         fully_acked = 0;
3196                         end_seq = tp->snd_una;
3197                 } else {
3198                         acked_pcount = tcp_skb_pcount(skb);
3199                         end_seq = scb->end_seq;
3200                 }
3201
3202                 /* MTU probing checks */
3203                 if (fully_acked && icsk->icsk_mtup.probe_size &&
3204                     !after(tp->mtu_probe.probe_seq_end, scb->end_seq)) {
3205                         tcp_mtup_probe_success(sk, skb);
3206                 }
3207
3208                 if (sacked & TCPCB_RETRANS) {
3209                         if (sacked & TCPCB_SACKED_RETRANS)
3210                                 tp->retrans_out -= acked_pcount;
3211                         flag |= FLAG_RETRANS_DATA_ACKED;
3212                         ca_seq_rtt = -1;
3213                         seq_rtt = -1;
3214                         if ((flag & FLAG_DATA_ACKED) || (acked_pcount > 1))
3215                                 flag |= FLAG_NONHEAD_RETRANS_ACKED;
3216                 } else {
3217                         ca_seq_rtt = now - scb->when;
3218                         last_ackt = skb->tstamp;
3219                         if (seq_rtt < 0) {
3220                                 seq_rtt = ca_seq_rtt;
3221                         }
3222                         if (!(sacked & TCPCB_SACKED_ACKED))
3223                                 reord = min(pkts_acked, reord);
3224                 }
3225
3226                 if (sacked & TCPCB_SACKED_ACKED)
3227                         tp->sacked_out -= acked_pcount;
3228                 if (sacked & TCPCB_LOST)
3229                         tp->lost_out -= acked_pcount;
3230
3231                 tp->packets_out -= acked_pcount;
3232                 pkts_acked += acked_pcount;
3233
3234                 /* Initial outgoing SYN's get put onto the write_queue
3235                  * just like anything else we transmit.  It is not
3236                  * true data, and if we misinform our callers that
3237                  * this ACK acks real data, we will erroneously exit
3238                  * connection startup slow start one packet too
3239                  * quickly.  This is severely frowned upon behavior.
3240                  */
3241                 if (!(scb->flags & TCPCB_FLAG_SYN)) {
3242                         flag |= FLAG_DATA_ACKED;
3243                 } else {
3244                         flag |= FLAG_SYN_ACKED;
3245                         tp->retrans_stamp = 0;
3246                 }
3247
3248                 if (!fully_acked)
3249                         break;
3250
3251                 tcp_unlink_write_queue(skb, sk);
3252                 sk_wmem_free_skb(sk, skb);
3253                 tp->scoreboard_skb_hint = NULL;
3254                 if (skb == tp->retransmit_skb_hint)
3255                         tp->retransmit_skb_hint = NULL;
3256                 if (skb == tp->lost_skb_hint)
3257                         tp->lost_skb_hint = NULL;
3258         }
3259
3260         if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3261                 tp->snd_up = tp->snd_una;
3262
3263         if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3264                 flag |= FLAG_SACK_RENEGING;
3265
3266         if (flag & FLAG_ACKED) {
3267                 const struct tcp_congestion_ops *ca_ops
3268                         = inet_csk(sk)->icsk_ca_ops;
3269
3270                 tcp_ack_update_rtt(sk, flag, seq_rtt);
3271                 tcp_rearm_rto(sk);
3272
3273                 if (tcp_is_reno(tp)) {
3274                         tcp_remove_reno_sacks(sk, pkts_acked);
3275                 } else {
3276                         /* Non-retransmitted hole got filled? That's reordering */
3277                         if (reord < prior_fackets)
3278                                 tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3279
3280                         /* No need to care for underflows here because
3281                          * the lost_skb_hint gets NULLed if we're past it
3282                          * (or something non-trivial happened)
3283                          */
3284                         if (tcp_is_fack(tp))
3285                                 tp->lost_cnt_hint -= pkts_acked;
3286                         else
3287                                 tp->lost_cnt_hint -= prior_sacked - tp->sacked_out;
3288                 }
3289
3290                 tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3291
3292                 if (ca_ops->pkts_acked) {
3293                         s32 rtt_us = -1;
3294
3295                         /* Is the ACK triggering packet unambiguous? */
3296                         if (!(flag & FLAG_RETRANS_DATA_ACKED)) {
3297                                 /* High resolution needed and available? */
3298                                 if (ca_ops->flags & TCP_CONG_RTT_STAMP &&
3299                                     !ktime_equal(last_ackt,
3300                                                  net_invalid_timestamp()))
3301                                         rtt_us = ktime_us_delta(ktime_get_real(),
3302                                                                 last_ackt);
3303                                 else if (ca_seq_rtt > 0)
3304                                         rtt_us = jiffies_to_usecs(ca_seq_rtt);
3305                         }
3306
3307                         ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
3308                 }
3309         }
3310
3311 #if FASTRETRANS_DEBUG > 0
3312         WARN_ON((int)tp->sacked_out < 0);
3313         WARN_ON((int)tp->lost_out < 0);
3314         WARN_ON((int)tp->retrans_out < 0);
3315         if (!tp->packets_out && tcp_is_sack(tp)) {
3316                 icsk = inet_csk(sk);
3317                 if (tp->lost_out) {
3318                         printk(KERN_DEBUG "Leak l=%u %d\n",
3319                                tp->lost_out, icsk->icsk_ca_state);
3320                         tp->lost_out = 0;
3321                 }
3322                 if (tp->sacked_out) {
3323                         printk(KERN_DEBUG "Leak s=%u %d\n",
3324                                tp->sacked_out, icsk->icsk_ca_state);
3325                         tp->sacked_out = 0;
3326                 }
3327                 if (tp->retrans_out) {
3328                         printk(KERN_DEBUG "Leak r=%u %d\n",
3329                                tp->retrans_out, icsk->icsk_ca_state);
3330                         tp->retrans_out = 0;
3331                 }
3332         }
3333 #endif
3334         return flag;
3335 }
3336
3337 static void tcp_ack_probe(struct sock *sk)
3338 {
3339         const struct tcp_sock *tp = tcp_sk(sk);
3340         struct inet_connection_sock *icsk = inet_csk(sk);
3341
3342         /* Was it a usable window open? */
3343
3344         if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
3345                 icsk->icsk_backoff = 0;
3346                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3347                 /* Socket must be waked up by subsequent tcp_data_snd_check().
3348                  * This function is not for random using!
3349                  */
3350         } else {
3351                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3352                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
3353                                           TCP_RTO_MAX);
3354         }
3355 }
3356
3357 static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
3358 {
3359         return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3360                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
3361 }
3362
3363 static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3364 {
3365         const struct tcp_sock *tp = tcp_sk(sk);
3366         return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
3367                 !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
3368 }
3369
3370 /* Check that window update is acceptable.
3371  * The function assumes that snd_una<=ack<=snd_next.
3372  */
3373 static inline int tcp_may_update_window(const struct tcp_sock *tp,
3374                                         const u32 ack, const u32 ack_seq,
3375                                         const u32 nwin)
3376 {
3377         return (after(ack, tp->snd_una) ||
3378                 after(ack_seq, tp->snd_wl1) ||
3379                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
3380 }
3381
3382 /* Update our send window.
3383  *
3384  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3385  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3386  */
3387 static int tcp_ack_update_window(struct sock *sk, struct sk_buff *skb, u32 ack,
3388                                  u32 ack_seq)
3389 {
3390         struct tcp_sock *tp = tcp_sk(sk);
3391         int flag = 0;
3392         u32 nwin = ntohs(tcp_hdr(skb)->window);
3393
3394         if (likely(!tcp_hdr(skb)->syn))
3395                 nwin <<= tp->rx_opt.snd_wscale;
3396
3397         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3398                 flag |= FLAG_WIN_UPDATE;
3399                 tcp_update_wl(tp, ack, ack_seq);
3400
3401                 if (tp->snd_wnd != nwin) {
3402                         tp->snd_wnd = nwin;
3403
3404                         /* Note, it is the only place, where
3405                          * fast path is recovered for sending TCP.
3406                          */
3407                         tp->pred_flags = 0;
3408                         tcp_fast_path_check(sk);
3409
3410                         if (nwin > tp->max_window) {
3411                                 tp->max_window = nwin;
3412                                 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3413                         }
3414                 }
3415         }
3416
3417         tp->snd_una = ack;
3418
3419         return flag;
3420 }
3421
3422 /* A very conservative spurious RTO response algorithm: reduce cwnd and
3423  * continue in congestion avoidance.
3424  */
3425 static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
3426 {
3427         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
3428         tp->snd_cwnd_cnt = 0;
3429         tp->bytes_acked = 0;
3430         TCP_ECN_queue_cwr(tp);
3431         tcp_moderate_cwnd(tp);
3432 }
3433
3434 /* A conservative spurious RTO response algorithm: reduce cwnd using
3435  * rate halving and continue in congestion avoidance.
3436  */
3437 static void tcp_ratehalving_spur_to_response(struct sock *sk)
3438 {
3439         tcp_enter_cwr(sk, 0);
3440 }
3441
3442 static void tcp_undo_spur_to_response(struct sock *sk, int flag)
3443 {
3444         if (flag & FLAG_ECE)
3445                 tcp_ratehalving_spur_to_response(sk);
3446         else
3447                 tcp_undo_cwr(sk, 1);
3448 }
3449
3450 /* F-RTO spurious RTO detection algorithm (RFC4138)
3451  *
3452  * F-RTO affects during two new ACKs following RTO (well, almost, see inline
3453  * comments). State (ACK number) is kept in frto_counter. When ACK advances
3454  * window (but not to or beyond highest sequence sent before RTO):
3455  *   On First ACK,  send two new segments out.
3456  *   On Second ACK, RTO was likely spurious. Do spurious response (response
3457  *                  algorithm is not part of the F-RTO detection algorithm
3458  *                  given in RFC4138 but can be selected separately).
3459  * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
3460  * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
3461  * of Nagle, this is done using frto_counter states 2 and 3, when a new data
3462  * segment of any size sent during F-RTO, state 2 is upgraded to 3.
3463  *
3464  * Rationale: if the RTO was spurious, new ACKs should arrive from the
3465  * original window even after we transmit two new data segments.
3466  *
3467  * SACK version:
3468  *   on first step, wait until first cumulative ACK arrives, then move to
3469  *   the second step. In second step, the next ACK decides.
3470  *
3471  * F-RTO is implemented (mainly) in four functions:
3472  *   - tcp_use_frto() is used to determine if TCP is can use F-RTO
3473  *   - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
3474  *     called when tcp_use_frto() showed green light
3475  *   - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
3476  *   - tcp_enter_frto_loss() is called if there is not enough evidence
3477  *     to prove that the RTO is indeed spurious. It transfers the control
3478  *     from F-RTO to the conventional RTO recovery
3479  */
3480 static int tcp_process_frto(struct sock *sk, int flag)
3481 {
3482         struct tcp_sock *tp = tcp_sk(sk);
3483
3484         tcp_verify_left_out(tp);
3485
3486         /* Duplicate the behavior from Loss state (fastretrans_alert) */
3487         if (flag & FLAG_DATA_ACKED)
3488                 inet_csk(sk)->icsk_retransmits = 0;
3489
3490         if ((flag & FLAG_NONHEAD_RETRANS_ACKED) ||
3491             ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
3492                 tp->undo_marker = 0;
3493
3494         if (!before(tp->snd_una, tp->frto_highmark)) {
3495                 tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
3496                 return 1;
3497         }
3498
3499         if (!tcp_is_sackfrto(tp)) {
3500                 /* RFC4138 shortcoming in step 2; should also have case c):
3501                  * ACK isn't duplicate nor advances window, e.g., opposite dir
3502                  * data, winupdate
3503                  */
3504                 if (!(flag & FLAG_ANY_PROGRESS) && (flag & FLAG_NOT_DUP))
3505                         return 1;
3506
3507                 if (!(flag & FLAG_DATA_ACKED)) {
3508                         tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
3509                                             flag);
3510                         return 1;
3511                 }
3512         } else {
3513                 if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
3514                         /* Prevent sending of new data. */
3515                         tp->snd_cwnd = min(tp->snd_cwnd,
3516                                            tcp_packets_in_flight(tp));
3517                         return 1;
3518                 }
3519
3520                 if ((tp->frto_counter >= 2) &&
3521                     (!(flag & FLAG_FORWARD_PROGRESS) ||
3522                      ((flag & FLAG_DATA_SACKED) &&
3523                       !(flag & FLAG_ONLY_ORIG_SACKED)))) {
3524                         /* RFC4138 shortcoming (see comment above) */
3525                         if (!(flag & FLAG_FORWARD_PROGRESS) &&
3526                             (flag & FLAG_NOT_DUP))
3527                                 return 1;
3528
3529                         tcp_enter_frto_loss(sk, 3, flag);
3530                         return 1;
3531                 }
3532         }
3533
3534         if (tp->frto_counter == 1) {
3535                 /* tcp_may_send_now needs to see updated state */
3536                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
3537                 tp->frto_counter = 2;
3538
3539                 if (!tcp_may_send_now(sk))
3540                         tcp_enter_frto_loss(sk, 2, flag);
3541
3542                 return 1;
3543         } else {
3544                 switch (sysctl_tcp_frto_response) {
3545                 case 2:
3546                         tcp_undo_spur_to_response(sk, flag);
3547                         break;
3548                 case 1:
3549                         tcp_conservative_spur_to_response(tp);
3550                         break;
3551                 default:
3552                         tcp_ratehalving_spur_to_response(sk);
3553                         break;
3554                 }
3555                 tp->frto_counter = 0;
3556                 tp->undo_marker = 0;
3557                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSPURIOUSRTOS);
3558         }
3559         return 0;
3560 }
3561
3562 /* This routine deals with incoming acks, but not outgoing ones. */
3563 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
3564 {
3565         struct inet_connection_sock *icsk = inet_csk(sk);
3566         struct tcp_sock *tp = tcp_sk(sk);
3567         u32 prior_snd_una = tp->snd_una;
3568         u32 ack_seq = TCP_SKB_CB(skb)->seq;
3569         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3570         u32 prior_in_flight;
3571         u32 prior_fackets;
3572         int prior_packets;
3573         int frto_cwnd = 0;
3574
3575         /* If the ack is newer than sent or older than previous acks
3576          * then we can probably ignore it.
3577          */
3578         if (after(ack, tp->snd_nxt))
3579                 goto uninteresting_ack;
3580
3581         if (before(ack, prior_snd_una))
3582                 goto old_ack;
3583
3584         if (after(ack, prior_snd_una))
3585                 flag |= FLAG_SND_UNA_ADVANCED;
3586
3587         if (sysctl_tcp_abc) {
3588                 if (icsk->icsk_ca_state < TCP_CA_CWR)
3589                         tp->bytes_acked += ack - prior_snd_una;
3590                 else if (icsk->icsk_ca_state == TCP_CA_Loss)
3591                         /* we assume just one segment left network */
3592                         tp->bytes_acked += min(ack - prior_snd_una,
3593                                                tp->mss_cache);
3594         }
3595
3596         prior_fackets = tp->fackets_out;
3597         prior_in_flight = tcp_packets_in_flight(tp);
3598
3599         if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3600                 /* Window is constant, pure forward advance.
3601                  * No more checks are required.
3602                  * Note, we use the fact that SND.UNA>=SND.WL2.
3603                  */
3604                 tcp_update_wl(tp, ack, ack_seq);
3605                 tp->snd_una = ack;
3606                 flag |= FLAG_WIN_UPDATE;
3607
3608                 tcp_ca_event(sk, CA_EVENT_FAST_ACK);
3609
3610                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
3611         } else {
3612                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3613                         flag |= FLAG_DATA;
3614                 else
3615                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3616
3617                 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3618
3619                 if (TCP_SKB_CB(skb)->sacked)
3620                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3621
3622                 if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
3623                         flag |= FLAG_ECE;
3624
3625                 tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
3626         }
3627
3628         /* We passed data and got it acked, remove any soft error
3629          * log. Something worked...
3630          */
3631         sk->sk_err_soft = 0;
3632         icsk->icsk_probes_out = 0;
3633         tp->rcv_tstamp = tcp_time_stamp;
3634         prior_packets = tp->packets_out;
3635         if (!prior_packets)
3636                 goto no_queue;
3637
3638         /* See if we can take anything off of the retransmit queue. */
3639         flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
3640
3641         if (tp->frto_counter)
3642                 frto_cwnd = tcp_process_frto(sk, flag);
3643         /* Guarantee sacktag reordering detection against wrap-arounds */
3644         if (before(tp->frto_highmark, tp->snd_una))
3645                 tp->frto_highmark = 0;
3646
3647         if (tcp_ack_is_dubious(sk, flag)) {
3648                 /* Advance CWND, if state allows this. */
3649                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
3650                     tcp_may_raise_cwnd(sk, flag))
3651                         tcp_cong_avoid(sk, ack, prior_in_flight);
3652                 tcp_fastretrans_alert(sk, prior_packets - tp->packets_out,
3653                                       flag);
3654         } else {
3655                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
3656                         tcp_cong_avoid(sk, ack, prior_in_flight);
3657         }
3658
3659         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3660                 dst_confirm(sk->sk_dst_cache);
3661
3662         return 1;
3663
3664 no_queue:
3665         /* If this ack opens up a zero window, clear backoff.  It was
3666          * being used to time the probes, and is probably far higher than
3667          * it needs to be for normal retransmission.
3668          */
3669         if (tcp_send_head(sk))
3670                 tcp_ack_probe(sk);
3671         return 1;
3672
3673 old_ack:
3674         if (TCP_SKB_CB(skb)->sacked) {
3675                 tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3676                 if (icsk->icsk_ca_state == TCP_CA_Open)
3677                         tcp_try_keep_open(sk);
3678         }
3679
3680 uninteresting_ack:
3681         SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3682         return 0;
3683 }
3684
3685 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
3686  * But, this can also be called on packets in the established flow when
3687  * the fast version below fails.
3688  */
3689 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx,
3690                        int estab)
3691 {
3692         unsigned char *ptr;
3693         struct tcphdr *th = tcp_hdr(skb);
3694         int length = (th->doff * 4) - sizeof(struct tcphdr);
3695
3696         ptr = (unsigned char *)(th + 1);
3697         opt_rx->saw_tstamp = 0;
3698
3699         while (length > 0) {
3700                 int opcode = *ptr++;
3701                 int opsize;
3702
3703                 switch (opcode) {
3704                 case TCPOPT_EOL:
3705                         return;
3706                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
3707                         length--;
3708                         continue;
3709                 default:
3710                         opsize = *ptr++;
3711                         if (opsize < 2) /* "silly options" */
3712                                 return;
3713                         if (opsize > length)
3714                                 return; /* don't parse partial options */
3715                         switch (opcode) {
3716                         case TCPOPT_MSS:
3717                                 if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3718                                         u16 in_mss = get_unaligned_be16(ptr);
3719                                         if (in_mss) {
3720                                                 if (opt_rx->user_mss &&
3721                                                     opt_rx->user_mss < in_mss)
3722                                                         in_mss = opt_rx->user_mss;
3723                                                 opt_rx->mss_clamp = in_mss;
3724                                         }
3725                                 }
3726                                 break;
3727                         case TCPOPT_WINDOW:
3728                                 if (opsize == TCPOLEN_WINDOW && th->syn &&
3729                                     !estab && sysctl_tcp_window_scaling) {
3730                                         __u8 snd_wscale = *(__u8 *)ptr;
3731                                         opt_rx->wscale_ok = 1;
3732                                         if (snd_wscale > 14) {
3733                                                 if (net_ratelimit())
3734                                                         printk(KERN_INFO "tcp_parse_options: Illegal window "
3735                                                                "scaling value %d >14 received.\n",
3736                                                                snd_wscale);
3737                                                 snd_wscale = 14;
3738                                         }
3739                                         opt_rx->snd_wscale = snd_wscale;
3740                                 }
3741                                 break;
3742                         case TCPOPT_TIMESTAMP:
3743                                 if ((opsize == TCPOLEN_TIMESTAMP) &&
3744                                     ((estab && opt_rx->tstamp_ok) ||
3745                                      (!estab && sysctl_tcp_timestamps))) {
3746                                         opt_rx->saw_tstamp = 1;
3747                                         opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3748                                         opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3749                                 }
3750                                 break;
3751                         case TCPOPT_SACK_PERM:
3752                                 if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3753                                     !estab && sysctl_tcp_sack) {
3754                                         opt_rx->sack_ok = 1;
3755                                         tcp_sack_reset(opt_rx);
3756                                 }
3757                                 break;
3758
3759                         case TCPOPT_SACK:
3760                                 if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3761                                    !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3762                                    opt_rx->sack_ok) {
3763                                         TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3764                                 }
3765                                 break;
3766 #ifdef CONFIG_TCP_MD5SIG
3767                         case TCPOPT_MD5SIG:
3768                                 /*
3769                                  * The MD5 Hash has already been
3770                                  * checked (see tcp_v{4,6}_do_rcv()).
3771                                  */
3772                                 break;
3773 #endif
3774                         }
3775
3776                         ptr += opsize-2;
3777                         length -= opsize;
3778                 }
3779         }
3780 }
3781
3782 static int tcp_parse_aligned_timestamp(struct tcp_sock *tp, struct tcphdr *th)
3783 {
3784         __be32 *ptr = (__be32 *)(th + 1);
3785
3786         if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3787                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3788                 tp->rx_opt.saw_tstamp = 1;
3789                 ++ptr;
3790                 tp->rx_opt.rcv_tsval = ntohl(*ptr);
3791                 ++ptr;
3792                 tp->rx_opt.rcv_tsecr = ntohl(*ptr);
3793                 return 1;
3794         }
3795         return 0;
3796 }
3797
3798 /* Fast parse options. This hopes to only see timestamps.
3799  * If it is wrong it falls back on tcp_parse_options().
3800  */
3801 static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
3802                                   struct tcp_sock *tp)
3803 {
3804         if (th->doff == sizeof(struct tcphdr) >> 2) {
3805                 tp->rx_opt.saw_tstamp = 0;
3806                 return 0;
3807         } else if (tp->rx_opt.tstamp_ok &&
3808                    th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
3809                 if (tcp_parse_aligned_timestamp(tp, th))
3810                         return 1;
3811         }
3812         tcp_parse_options(skb, &tp->rx_opt, 1);
3813         return 1;
3814 }
3815
3816 #ifdef CONFIG_TCP_MD5SIG
3817 /*
3818  * Parse MD5 Signature option
3819  */
3820 u8 *tcp_parse_md5sig_option(struct tcphdr *th)
3821 {
3822         int length = (th->doff << 2) - sizeof (*th);
3823         u8 *ptr = (u8*)(th + 1);
3824
3825         /* If the TCP option is too short, we can short cut */
3826         if (length < TCPOLEN_MD5SIG)
3827                 return NULL;
3828
3829         while (length > 0) {
3830                 int opcode = *ptr++;
3831                 int opsize;
3832
3833                 switch(opcode) {
3834                 case TCPOPT_EOL:
3835                         return NULL;
3836                 case TCPOPT_NOP:
3837                         length--;
3838                         continue;
3839                 default:
3840                         opsize = *ptr++;
3841                         if (opsize < 2 || opsize > length)
3842                                 return NULL;
3843                         if (opcode == TCPOPT_MD5SIG)
3844                                 return ptr;
3845                 }
3846                 ptr += opsize - 2;
3847                 length -= opsize;
3848         }
3849         return NULL;
3850 }
3851 #endif
3852
3853 static inline void tcp_store_ts_recent(struct tcp_sock *tp)
3854 {
3855         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3856         tp->rx_opt.ts_recent_stamp = get_seconds();
3857 }
3858
3859 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3860 {
3861         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3862                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3863                  * extra check below makes sure this can only happen
3864                  * for pure ACK frames.  -DaveM
3865                  *
3866                  * Not only, also it occurs for expired timestamps.
3867                  */
3868
3869                 if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
3870                    get_seconds() >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
3871                         tcp_store_ts_recent(tp);
3872         }
3873 }
3874
3875 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3876  *
3877  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3878  * it can pass through stack. So, the following predicate verifies that
3879  * this segment is not used for anything but congestion avoidance or
3880  * fast retransmit. Moreover, we even are able to eliminate most of such
3881  * second order effects, if we apply some small "replay" window (~RTO)
3882  * to timestamp space.
3883  *
3884  * All these measures still do not guarantee that we reject wrapped ACKs
3885  * on networks with high bandwidth, when sequence space is recycled fastly,
3886  * but it guarantees that such events will be very rare and do not affect
3887  * connection seriously. This doesn't look nice, but alas, PAWS is really
3888  * buggy extension.
3889  *
3890  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3891  * states that events when retransmit arrives after original data are rare.
3892  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3893  * the biggest problem on large power networks even with minor reordering.
3894  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3895  * up to bandwidth of 18Gigabit/sec. 8) ]
3896  */
3897
3898 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3899 {
3900         struct tcp_sock *tp = tcp_sk(sk);
3901         struct tcphdr *th = tcp_hdr(skb);
3902         u32 seq = TCP_SKB_CB(skb)->seq;
3903         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3904
3905         return (/* 1. Pure ACK with correct sequence number. */
3906                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3907
3908                 /* 2. ... and duplicate ACK. */
3909                 ack == tp->snd_una &&
3910
3911                 /* 3. ... and does not update window. */
3912                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3913
3914                 /* 4. ... and sits in replay window. */
3915                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3916 }
3917
3918 static inline int tcp_paws_discard(const struct sock *sk,
3919                                    const struct sk_buff *skb)
3920 {
3921         const struct tcp_sock *tp = tcp_sk(sk);
3922         return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
3923                 get_seconds() < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
3924                 !tcp_disordered_ack(sk, skb));
3925 }
3926
3927 /* Check segment sequence number for validity.
3928  *
3929  * Segment controls are considered valid, if the segment
3930  * fits to the window after truncation to the window. Acceptability
3931  * of data (and SYN, FIN, of course) is checked separately.
3932  * See tcp_data_queue(), for example.
3933  *
3934  * Also, controls (RST is main one) are accepted using RCV.WUP instead
3935  * of RCV.NXT. Peer still did not advance his SND.UNA when we
3936  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
3937  * (borrowed from freebsd)
3938  */
3939
3940 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
3941 {
3942         return  !before(end_seq, tp->rcv_wup) &&
3943                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
3944 }
3945
3946 /* When we get a reset we do this. */
3947 static void tcp_reset(struct sock *sk)
3948 {
3949         /* We want the right error as BSD sees it (and indeed as we do). */
3950         switch (sk->sk_state) {
3951         case TCP_SYN_SENT:
3952                 sk->sk_err = ECONNREFUSED;
3953                 break;
3954         case TCP_CLOSE_WAIT:
3955                 sk->sk_err = EPIPE;
3956                 break;
3957         case TCP_CLOSE:
3958                 return;
3959         default:
3960                 sk->sk_err = ECONNRESET;
3961         }
3962
3963         if (!sock_flag(sk, SOCK_DEAD))
3964                 sk->sk_error_report(sk);
3965
3966         tcp_done(sk);
3967 }
3968
3969 /*
3970  *      Process the FIN bit. This now behaves as it is supposed to work
3971  *      and the FIN takes effect when it is validly part of sequence
3972  *      space. Not before when we get holes.
3973  *
3974  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
3975  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
3976  *      TIME-WAIT)
3977  *
3978  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
3979  *      close and we go into CLOSING (and later onto TIME-WAIT)
3980  *
3981  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
3982  */
3983 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
3984 {
3985         struct tcp_sock *tp = tcp_sk(sk);
3986
3987         inet_csk_schedule_ack(sk);
3988
3989         sk->sk_shutdown |= RCV_SHUTDOWN;
3990         sock_set_flag(sk, SOCK_DONE);
3991
3992         switch (sk->sk_state) {
3993         case TCP_SYN_RECV:
3994         case TCP_ESTABLISHED:
3995                 /* Move to CLOSE_WAIT */
3996                 tcp_set_state(sk, TCP_CLOSE_WAIT);
3997                 inet_csk(sk)->icsk_ack.pingpong = 1;
3998                 break;
3999
4000         case TCP_CLOSE_WAIT:
4001         case TCP_CLOSING:
4002                 /* Received a retransmission of the FIN, do
4003                  * nothing.
4004                  */
4005                 break;
4006         case TCP_LAST_ACK:
4007                 /* RFC793: Remain in the LAST-ACK state. */
4008                 break;
4009
4010         case TCP_FIN_WAIT1:
4011                 /* This case occurs when a simultaneous close
4012                  * happens, we must ack the received FIN and
4013                  * enter the CLOSING state.
4014                  */
4015                 tcp_send_ack(sk);
4016                 tcp_set_state(sk, TCP_CLOSING);
4017                 break;
4018         case TCP_FIN_WAIT2:
4019                 /* Received a FIN -- send ACK and enter TIME_WAIT. */
4020                 tcp_send_ack(sk);
4021                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4022                 break;
4023         default:
4024                 /* Only TCP_LISTEN and TCP_CLOSE are left, in these
4025                  * cases we should never reach this piece of code.
4026                  */
4027                 printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
4028                        __func__, sk->sk_state);
4029                 break;
4030         }
4031
4032         /* It _is_ possible, that we have something out-of-order _after_ FIN.
4033          * Probably, we should reset in this case. For now drop them.
4034          */
4035         __skb_queue_purge(&tp->out_of_order_queue);
4036         if (tcp_is_sack(tp))
4037                 tcp_sack_reset(&tp->rx_opt);
4038         sk_mem_reclaim(sk);
4039
4040         if (!sock_flag(sk, SOCK_DEAD)) {
4041                 sk->sk_state_change(sk);
4042
4043                 /* Do not send POLL_HUP for half duplex close. */
4044                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
4045                     sk->sk_state == TCP_CLOSE)
4046                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4047                 else
4048                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4049         }
4050 }
4051
4052 static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4053                                   u32 end_seq)
4054 {
4055         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4056                 if (before(seq, sp->start_seq))
4057                         sp->start_seq = seq;
4058                 if (after(end_seq, sp->end_seq))
4059                         sp->end_seq = end_seq;
4060                 return 1;
4061         }
4062         return 0;
4063 }
4064
4065 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4066 {
4067         struct tcp_sock *tp = tcp_sk(sk);
4068
4069         if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4070                 int mib_idx;
4071
4072                 if (before(seq, tp->rcv_nxt))
4073                         mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4074                 else
4075                         mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4076
4077                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
4078
4079                 tp->rx_opt.dsack = 1;
4080                 tp->duplicate_sack[0].start_seq = seq;
4081                 tp->duplicate_sack[0].end_seq = end_seq;
4082                 tp->rx_opt.eff_sacks = tp->rx_opt.num_sacks + 1;
4083         }
4084 }
4085
4086 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4087 {
4088         struct tcp_sock *tp = tcp_sk(sk);
4089
4090         if (!tp->rx_opt.dsack)
4091                 tcp_dsack_set(sk, seq, end_seq);
4092         else
4093                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4094 }
4095
4096 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
4097 {
4098         struct tcp_sock *tp = tcp_sk(sk);
4099
4100         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4101             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4102                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4103                 tcp_enter_quickack_mode(sk);
4104
4105                 if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4106                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4107
4108                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4109                                 end_seq = tp->rcv_nxt;
4110                         tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4111                 }
4112         }
4113
4114         tcp_send_ack(sk);
4115 }
4116
4117 /* These routines update the SACK block as out-of-order packets arrive or
4118  * in-order packets close up the sequence space.
4119  */
4120 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4121 {
4122         int this_sack;
4123         struct tcp_sack_block *sp = &tp->selective_acks[0];
4124         struct tcp_sack_block *swalk = sp + 1;
4125
4126         /* See if the recent change to the first SACK eats into
4127          * or hits the sequence space of other SACK blocks, if so coalesce.
4128          */
4129         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4130                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4131                         int i;
4132
4133                         /* Zap SWALK, by moving every further SACK up by one slot.
4134                          * Decrease num_sacks.
4135                          */
4136                         tp->rx_opt.num_sacks--;
4137                         tp->rx_opt.eff_sacks = tp->rx_opt.num_sacks +
4138                                                tp->rx_opt.dsack;
4139                         for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4140                                 sp[i] = sp[i + 1];
4141                         continue;
4142                 }
4143                 this_sack++, swalk++;
4144         }
4145 }
4146
4147 static inline void tcp_sack_swap(struct tcp_sack_block *sack1,
4148                                  struct tcp_sack_block *sack2)
4149 {
4150         __u32 tmp;
4151
4152         tmp = sack1->start_seq;
4153         sack1->start_seq = sack2->start_seq;
4154         sack2->start_seq = tmp;
4155
4156         tmp = sack1->end_seq;
4157         sack1->end_seq = sack2->end_seq;
4158         sack2->end_seq = tmp;
4159 }
4160
4161 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4162 {
4163         struct tcp_sock *tp = tcp_sk(sk);
4164         struct tcp_sack_block *sp = &tp->selective_acks[0];
4165         int cur_sacks = tp->rx_opt.num_sacks;
4166         int this_sack;
4167
4168         if (!cur_sacks)
4169                 goto new_sack;
4170
4171         for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4172                 if (tcp_sack_extend(sp, seq, end_seq)) {
4173                         /* Rotate this_sack to the first one. */
4174                         for (; this_sack > 0; this_sack--, sp--)
4175                                 tcp_sack_swap(sp, sp - 1);
4176                         if (cur_sacks > 1)
4177                                 tcp_sack_maybe_coalesce(tp);
4178                         return;
4179                 }
4180         }
4181
4182         /* Could not find an adjacent existing SACK, build a new one,
4183          * put it at the front, and shift everyone else down.  We
4184          * always know there is at least one SACK present already here.
4185          *
4186          * If the sack array is full, forget about the last one.
4187          */
4188         if (this_sack >= TCP_NUM_SACKS) {
4189                 this_sack--;
4190                 tp->rx_opt.num_sacks--;
4191                 sp--;
4192         }
4193         for (; this_sack > 0; this_sack--, sp--)
4194                 *sp = *(sp - 1);
4195
4196 new_sack:
4197         /* Build the new head SACK, and we're done. */
4198         sp->start_seq = seq;
4199         sp->end_seq = end_seq;
4200         tp->rx_opt.num_sacks++;
4201         tp->rx_opt.eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
4202 }
4203
4204 /* RCV.NXT advances, some SACKs should be eaten. */
4205
4206 static void tcp_sack_remove(struct tcp_sock *tp)
4207 {
4208         struct tcp_sack_block *sp = &tp->selective_acks[0];
4209         int num_sacks = tp->rx_opt.num_sacks;
4210         int this_sack;
4211
4212         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4213         if (skb_queue_empty(&tp->out_of_order_queue)) {
4214                 tp->rx_opt.num_sacks = 0;
4215                 tp->rx_opt.eff_sacks = tp->rx_opt.dsack;
4216                 return;
4217         }
4218
4219         for (this_sack = 0; this_sack < num_sacks;) {
4220                 /* Check if the start of the sack is covered by RCV.NXT. */
4221                 if (!before(tp->rcv_nxt, sp->start_seq)) {
4222                         int i;
4223
4224                         /* RCV.NXT must cover all the block! */
4225                         WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4226
4227                         /* Zap this SACK, by moving forward any other SACKS. */
4228                         for (i=this_sack+1; i < num_sacks; i++)
4229                                 tp->selective_acks[i-1] = tp->selective_acks[i];
4230                         num_sacks--;
4231                         continue;
4232                 }
4233                 this_sack++;
4234                 sp++;
4235         }
4236         if (num_sacks != tp->rx_opt.num_sacks) {
4237                 tp->rx_opt.num_sacks = num_sacks;
4238                 tp->rx_opt.eff_sacks = tp->rx_opt.num_sacks +
4239                                        tp->rx_opt.dsack;
4240         }
4241 }
4242
4243 /* This one checks to see if we can put data from the
4244  * out_of_order queue into the receive_queue.
4245  */
4246 static void tcp_ofo_queue(struct sock *sk)
4247 {
4248         struct tcp_sock *tp = tcp_sk(sk);
4249         __u32 dsack_high = tp->rcv_nxt;
4250         struct sk_buff *skb;
4251
4252         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
4253                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4254                         break;
4255
4256                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4257                         __u32 dsack = dsack_high;
4258                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4259                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
4260                         tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4261                 }
4262
4263                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4264                         SOCK_DEBUG(sk, "ofo packet was already received \n");
4265                         __skb_unlink(skb, &tp->out_of_order_queue);
4266                         __kfree_skb(skb);
4267                         continue;
4268                 }
4269                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4270                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4271                            TCP_SKB_CB(skb)->end_seq);
4272
4273                 __skb_unlink(skb, &tp->out_of_order_queue);
4274                 __skb_queue_tail(&sk->sk_receive_queue, skb);
4275                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4276                 if (tcp_hdr(skb)->fin)
4277                         tcp_fin(skb, sk, tcp_hdr(skb));
4278         }
4279 }
4280
4281 static int tcp_prune_ofo_queue(struct sock *sk);
4282 static int tcp_prune_queue(struct sock *sk);
4283
4284 static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size)
4285 {
4286         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4287             !sk_rmem_schedule(sk, size)) {
4288
4289                 if (tcp_prune_queue(sk) < 0)
4290                         return -1;
4291
4292                 if (!sk_rmem_schedule(sk, size)) {
4293                         if (!tcp_prune_ofo_queue(sk))
4294                                 return -1;
4295
4296                         if (!sk_rmem_schedule(sk, size))
4297                                 return -1;
4298                 }
4299         }
4300         return 0;
4301 }
4302
4303 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4304 {
4305         struct tcphdr *th = tcp_hdr(skb);
4306         struct tcp_sock *tp = tcp_sk(sk);
4307         int eaten = -1;
4308
4309         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
4310                 goto drop;
4311
4312         __skb_pull(skb, th->doff * 4);
4313
4314         TCP_ECN_accept_cwr(tp, skb);
4315
4316         if (tp->rx_opt.dsack) {
4317                 tp->rx_opt.dsack = 0;
4318                 tp->rx_opt.eff_sacks = tp->rx_opt.num_sacks;
4319         }
4320
4321         /*  Queue data for delivery to the user.
4322          *  Packets in sequence go to the receive queue.
4323          *  Out of sequence packets to the out_of_order_queue.
4324          */
4325         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4326                 if (tcp_receive_window(tp) == 0)
4327                         goto out_of_window;
4328
4329                 /* Ok. In sequence. In window. */
4330                 if (tp->ucopy.task == current &&
4331                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4332                     sock_owned_by_user(sk) && !tp->urg_data) {
4333                         int chunk = min_t(unsigned int, skb->len,
4334                                           tp->ucopy.len);
4335
4336                         __set_current_state(TASK_RUNNING);
4337
4338                         local_bh_enable();
4339                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
4340                                 tp->ucopy.len -= chunk;
4341                                 tp->copied_seq += chunk;
4342                                 eaten = (chunk == skb->len && !th->fin);
4343                                 tcp_rcv_space_adjust(sk);
4344                         }
4345                         local_bh_disable();
4346                 }
4347
4348                 if (eaten <= 0) {
4349 queue_and_out:
4350                         if (eaten < 0 &&
4351                             tcp_try_rmem_schedule(sk, skb->truesize))
4352                                 goto drop;
4353
4354                         skb_set_owner_r(skb, sk);
4355                         __skb_queue_tail(&sk->sk_receive_queue, skb);
4356                 }
4357                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4358                 if (skb->len)
4359                         tcp_event_data_recv(sk, skb);
4360                 if (th->fin)
4361                         tcp_fin(skb, sk, th);
4362
4363                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
4364                         tcp_ofo_queue(sk);
4365
4366                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
4367                          * gap in queue is filled.
4368                          */
4369                         if (skb_queue_empty(&tp->out_of_order_queue))
4370                                 inet_csk(sk)->icsk_ack.pingpong = 0;
4371                 }
4372
4373                 if (tp->rx_opt.num_sacks)
4374                         tcp_sack_remove(tp);
4375
4376                 tcp_fast_path_check(sk);
4377
4378                 if (eaten > 0)
4379                         __kfree_skb(skb);
4380                 else if (!sock_flag(sk, SOCK_DEAD))
4381                         sk->sk_data_ready(sk, 0);
4382                 return;
4383         }
4384
4385         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4386                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
4387                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4388                 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4389
4390 out_of_window:
4391                 tcp_enter_quickack_mode(sk);
4392                 inet_csk_schedule_ack(sk);
4393 drop:
4394                 __kfree_skb(skb);
4395                 return;
4396         }
4397
4398         /* Out of window. F.e. zero window probe. */
4399         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4400                 goto out_of_window;
4401
4402         tcp_enter_quickack_mode(sk);
4403
4404         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4405                 /* Partial packet, seq < rcv_next < end_seq */
4406                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4407                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4408                            TCP_SKB_CB(skb)->end_seq);
4409
4410                 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4411
4412                 /* If window is closed, drop tail of packet. But after
4413                  * remembering D-SACK for its head made in previous line.
4414                  */
4415                 if (!tcp_receive_window(tp))
4416                         goto out_of_window;
4417                 goto queue_and_out;
4418         }
4419
4420         TCP_ECN_check_ce(tp, skb);
4421
4422         if (tcp_try_rmem_schedule(sk, skb->truesize))
4423                 goto drop;
4424
4425         /* Disable header prediction. */
4426         tp->pred_flags = 0;
4427         inet_csk_schedule_ack(sk);
4428
4429         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4430                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4431
4432         skb_set_owner_r(skb, sk);
4433
4434         if (!skb_peek(&tp->out_of_order_queue)) {
4435                 /* Initial out of order segment, build 1 SACK. */
4436                 if (tcp_is_sack(tp)) {
4437                         tp->rx_opt.num_sacks = 1;
4438                         tp->rx_opt.dsack     = 0;
4439                         tp->rx_opt.eff_sacks = 1;
4440                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
4441                         tp->selective_acks[0].end_seq =
4442                                                 TCP_SKB_CB(skb)->end_seq;
4443                 }
4444                 __skb_queue_head(&tp->out_of_order_queue, skb);
4445         } else {
4446                 struct sk_buff *skb1 = tp->out_of_order_queue.prev;
4447                 u32 seq = TCP_SKB_CB(skb)->seq;
4448                 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4449
4450                 if (seq == TCP_SKB_CB(skb1)->end_seq) {
4451                         __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4452
4453                         if (!tp->rx_opt.num_sacks ||
4454                             tp->selective_acks[0].end_seq != seq)
4455                                 goto add_sack;
4456
4457                         /* Common case: data arrive in order after hole. */
4458                         tp->selective_acks[0].end_seq = end_seq;
4459                         return;
4460                 }
4461
4462                 /* Find place to insert this segment. */
4463                 do {
4464                         if (!after(TCP_SKB_CB(skb1)->seq, seq))
4465                                 break;
4466                 } while ((skb1 = skb1->prev) !=
4467                          (struct sk_buff *)&tp->out_of_order_queue);
4468
4469                 /* Do skb overlap to previous one? */
4470                 if (skb1 != (struct sk_buff *)&tp->out_of_order_queue &&
4471                     before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4472                         if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4473                                 /* All the bits are present. Drop. */
4474                                 __kfree_skb(skb);
4475                                 tcp_dsack_set(sk, seq, end_seq);
4476                                 goto add_sack;
4477                         }
4478                         if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4479                                 /* Partial overlap. */
4480                                 tcp_dsack_set(sk, seq,
4481                                               TCP_SKB_CB(skb1)->end_seq);
4482                         } else {
4483                                 skb1 = skb1->prev;
4484                         }
4485                 }
4486                 __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4487
4488                 /* And clean segments covered by new one as whole. */
4489                 while ((skb1 = skb->next) !=
4490                        (struct sk_buff *)&tp->out_of_order_queue &&
4491                        after(end_seq, TCP_SKB_CB(skb1)->seq)) {
4492                         if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4493                                 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4494                                                  end_seq);
4495                                 break;
4496                         }
4497                         __skb_unlink(skb1, &tp->out_of_order_queue);
4498                         tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4499                                          TCP_SKB_CB(skb1)->end_seq);
4500                         __kfree_skb(skb1);
4501                 }
4502
4503 add_sack:
4504                 if (tcp_is_sack(tp))
4505                         tcp_sack_new_ofo_skb(sk, seq, end_seq);
4506         }
4507 }
4508
4509 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4510                                         struct sk_buff_head *list)
4511 {
4512         struct sk_buff *next = skb->next;
4513
4514         __skb_unlink(skb, list);
4515         __kfree_skb(skb);
4516         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4517
4518         return next;
4519 }
4520
4521 /* Collapse contiguous sequence of skbs head..tail with
4522  * sequence numbers start..end.
4523  * Segments with FIN/SYN are not collapsed (only because this
4524  * simplifies code)
4525  */
4526 static void
4527 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
4528              struct sk_buff *head, struct sk_buff *tail,
4529              u32 start, u32 end)
4530 {
4531         struct sk_buff *skb;
4532
4533         /* First, check that queue is collapsible and find
4534          * the point where collapsing can be useful. */
4535         for (skb = head; skb != tail;) {
4536                 /* No new bits? It is possible on ofo queue. */
4537                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4538                         skb = tcp_collapse_one(sk, skb, list);
4539                         continue;
4540                 }
4541
4542                 /* The first skb to collapse is:
4543                  * - not SYN/FIN and
4544                  * - bloated or contains data before "start" or
4545                  *   overlaps to the next one.
4546                  */
4547                 if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
4548                     (tcp_win_from_space(skb->truesize) > skb->len ||
4549                      before(TCP_SKB_CB(skb)->seq, start) ||
4550                      (skb->next != tail &&
4551                       TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
4552                         break;
4553
4554                 /* Decided to skip this, advance start seq. */
4555                 start = TCP_SKB_CB(skb)->end_seq;
4556                 skb = skb->next;
4557         }
4558         if (skb == tail || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
4559                 return;
4560
4561         while (before(start, end)) {
4562                 struct sk_buff *nskb;
4563                 unsigned int header = skb_headroom(skb);
4564                 int copy = SKB_MAX_ORDER(header, 0);
4565
4566                 /* Too big header? This can happen with IPv6. */
4567                 if (copy < 0)
4568                         return;
4569                 if (end - start < copy)
4570                         copy = end - start;
4571                 nskb = alloc_skb(copy + header, GFP_ATOMIC);
4572                 if (!nskb)
4573                         return;
4574
4575                 skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
4576                 skb_set_network_header(nskb, (skb_network_header(skb) -
4577                                               skb->head));
4578                 skb_set_transport_header(nskb, (skb_transport_header(skb) -
4579                                                 skb->head));
4580                 skb_reserve(nskb, header);
4581                 memcpy(nskb->head, skb->head, header);
4582                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4583                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4584                 __skb_queue_before(list, skb, nskb);
4585                 skb_set_owner_r(nskb, sk);
4586
4587                 /* Copy data, releasing collapsed skbs. */
4588                 while (copy > 0) {
4589                         int offset = start - TCP_SKB_CB(skb)->seq;
4590                         int size = TCP_SKB_CB(skb)->end_seq - start;
4591
4592                         BUG_ON(offset < 0);
4593                         if (size > 0) {
4594                                 size = min(copy, size);
4595                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4596                                         BUG();
4597                                 TCP_SKB_CB(nskb)->end_seq += size;
4598                                 copy -= size;
4599                                 start += size;
4600                         }
4601                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4602                                 skb = tcp_collapse_one(sk, skb, list);
4603                                 if (skb == tail ||
4604                                     tcp_hdr(skb)->syn ||
4605                                     tcp_hdr(skb)->fin)
4606                                         return;
4607                         }
4608                 }
4609         }
4610 }
4611
4612 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4613  * and tcp_collapse() them until all the queue is collapsed.
4614  */
4615 static void tcp_collapse_ofo_queue(struct sock *sk)
4616 {
4617         struct tcp_sock *tp = tcp_sk(sk);
4618         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
4619         struct sk_buff *head;
4620         u32 start, end;
4621
4622         if (skb == NULL)
4623                 return;
4624
4625         start = TCP_SKB_CB(skb)->seq;
4626         end = TCP_SKB_CB(skb)->end_seq;
4627         head = skb;
4628
4629         for (;;) {
4630                 skb = skb->next;
4631
4632                 /* Segment is terminated when we see gap or when
4633                  * we are at the end of all the queue. */
4634                 if (skb == (struct sk_buff *)&tp->out_of_order_queue ||
4635                     after(TCP_SKB_CB(skb)->seq, end) ||
4636                     before(TCP_SKB_CB(skb)->end_seq, start)) {
4637                         tcp_collapse(sk, &tp->out_of_order_queue,
4638                                      head, skb, start, end);
4639                         head = skb;
4640                         if (skb == (struct sk_buff *)&tp->out_of_order_queue)
4641                                 break;
4642                         /* Start new segment */
4643                         start = TCP_SKB_CB(skb)->seq;
4644                         end = TCP_SKB_CB(skb)->end_seq;
4645                 } else {
4646                         if (before(TCP_SKB_CB(skb)->seq, start))
4647                                 start = TCP_SKB_CB(skb)->seq;
4648                         if (after(TCP_SKB_CB(skb)->end_seq, end))
4649                                 end = TCP_SKB_CB(skb)->end_seq;
4650                 }
4651         }
4652 }
4653
4654 /*
4655  * Purge the out-of-order queue.
4656  * Return true if queue was pruned.
4657  */
4658 static int tcp_prune_ofo_queue(struct sock *sk)
4659 {
4660         struct tcp_sock *tp = tcp_sk(sk);
4661         int res = 0;
4662
4663         if (!skb_queue_empty(&tp->out_of_order_queue)) {
4664                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED);
4665                 __skb_queue_purge(&tp->out_of_order_queue);
4666
4667                 /* Reset SACK state.  A conforming SACK implementation will
4668                  * do the same at a timeout based retransmit.  When a connection
4669                  * is in a sad state like this, we care only about integrity
4670                  * of the connection not performance.
4671                  */
4672                 if (tp->rx_opt.sack_ok)
4673                         tcp_sack_reset(&tp->rx_opt);
4674                 sk_mem_reclaim(sk);
4675                 res = 1;
4676         }
4677         return res;
4678 }
4679
4680 /* Reduce allocated memory if we can, trying to get
4681  * the socket within its memory limits again.
4682  *
4683  * Return less than zero if we should start dropping frames
4684  * until the socket owning process reads some of the data
4685  * to stabilize the situation.
4686  */
4687 static int tcp_prune_queue(struct sock *sk)
4688 {
4689         struct tcp_sock *tp = tcp_sk(sk);
4690
4691         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4692
4693         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED);
4694
4695         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4696                 tcp_clamp_window(sk);
4697         else if (tcp_memory_pressure)
4698                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4699
4700         tcp_collapse_ofo_queue(sk);
4701         tcp_collapse(sk, &sk->sk_receive_queue,
4702                      sk->sk_receive_queue.next,
4703                      (struct sk_buff *)&sk->sk_receive_queue,
4704                      tp->copied_seq, tp->rcv_nxt);
4705         sk_mem_reclaim(sk);
4706
4707         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4708                 return 0;
4709
4710         /* Collapsing did not help, destructive actions follow.
4711          * This must not ever occur. */
4712
4713         tcp_prune_ofo_queue(sk);
4714
4715         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4716                 return 0;
4717
4718         /* If we are really being abused, tell the caller to silently
4719          * drop receive data on the floor.  It will get retransmitted
4720          * and hopefully then we'll have sufficient space.
4721          */
4722         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED);
4723
4724         /* Massive buffer overcommit. */
4725         tp->pred_flags = 0;
4726         return -1;
4727 }
4728
4729 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
4730  * As additional protections, we do not touch cwnd in retransmission phases,
4731  * and if application hit its sndbuf limit recently.
4732  */
4733 void tcp_cwnd_application_limited(struct sock *sk)
4734 {
4735         struct tcp_sock *tp = tcp_sk(sk);
4736
4737         if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
4738             sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
4739                 /* Limited by application or receiver window. */
4740                 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
4741                 u32 win_used = max(tp->snd_cwnd_used, init_win);
4742                 if (win_used < tp->snd_cwnd) {
4743                         tp->snd_ssthresh = tcp_current_ssthresh(sk);
4744                         tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
4745                 }
4746                 tp->snd_cwnd_used = 0;
4747         }
4748         tp->snd_cwnd_stamp = tcp_time_stamp;
4749 }
4750
4751 static int tcp_should_expand_sndbuf(struct sock *sk)
4752 {
4753         struct tcp_sock *tp = tcp_sk(sk);
4754
4755         /* If the user specified a specific send buffer setting, do
4756          * not modify it.
4757          */
4758         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4759                 return 0;
4760
4761         /* If we are under global TCP memory pressure, do not expand.  */
4762         if (tcp_memory_pressure)
4763                 return 0;
4764
4765         /* If we are under soft global TCP memory pressure, do not expand.  */
4766         if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
4767                 return 0;
4768
4769         /* If we filled the congestion window, do not expand.  */
4770         if (tp->packets_out >= tp->snd_cwnd)
4771                 return 0;
4772
4773         return 1;
4774 }
4775
4776 /* When incoming ACK allowed to free some skb from write_queue,
4777  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
4778  * on the exit from tcp input handler.
4779  *
4780  * PROBLEM: sndbuf expansion does not work well with largesend.
4781  */
4782 static void tcp_new_space(struct sock *sk)
4783 {
4784         struct tcp_sock *tp = tcp_sk(sk);
4785
4786         if (tcp_should_expand_sndbuf(sk)) {
4787                 int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
4788                         MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
4789                 int demanded = max_t(unsigned int, tp->snd_cwnd,
4790                                      tp->reordering + 1);
4791                 sndmem *= 2 * demanded;
4792                 if (sndmem > sk->sk_sndbuf)
4793                         sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
4794                 tp->snd_cwnd_stamp = tcp_time_stamp;
4795         }
4796
4797         sk->sk_write_space(sk);
4798 }
4799
4800 static void tcp_check_space(struct sock *sk)
4801 {
4802         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
4803                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
4804                 if (sk->sk_socket &&
4805                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
4806                         tcp_new_space(sk);
4807         }
4808 }
4809
4810 static inline void tcp_data_snd_check(struct sock *sk)
4811 {
4812         tcp_push_pending_frames(sk);
4813         tcp_check_space(sk);
4814 }
4815
4816 /*
4817  * Check if sending an ack is needed.
4818  */
4819 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
4820 {
4821         struct tcp_sock *tp = tcp_sk(sk);
4822
4823             /* More than one full frame received... */
4824         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
4825              /* ... and right edge of window advances far enough.
4826               * (tcp_recvmsg() will send ACK otherwise). Or...
4827               */
4828              && __tcp_select_window(sk) >= tp->rcv_wnd) ||
4829             /* We ACK each frame or... */
4830             tcp_in_quickack_mode(sk) ||
4831             /* We have out of order data. */
4832             (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
4833                 /* Then ack it now */
4834                 tcp_send_ack(sk);
4835         } else {
4836                 /* Else, send delayed ack. */
4837                 tcp_send_delayed_ack(sk);
4838         }
4839 }
4840
4841 static inline void tcp_ack_snd_check(struct sock *sk)
4842 {
4843         if (!inet_csk_ack_scheduled(sk)) {
4844                 /* We sent a data segment already. */
4845                 return;
4846         }
4847         __tcp_ack_snd_check(sk, 1);
4848 }
4849
4850 /*
4851  *      This routine is only called when we have urgent data
4852  *      signaled. Its the 'slow' part of tcp_urg. It could be
4853  *      moved inline now as tcp_urg is only called from one
4854  *      place. We handle URGent data wrong. We have to - as
4855  *      BSD still doesn't use the correction from RFC961.
4856  *      For 1003.1g we should support a new option TCP_STDURG to permit
4857  *      either form (or just set the sysctl tcp_stdurg).
4858  */
4859
4860 static void tcp_check_urg(struct sock *sk, struct tcphdr *th)
4861 {
4862         struct tcp_sock *tp = tcp_sk(sk);
4863         u32 ptr = ntohs(th->urg_ptr);
4864
4865         if (ptr && !sysctl_tcp_stdurg)
4866                 ptr--;
4867         ptr += ntohl(th->seq);
4868
4869         /* Ignore urgent data that we've already seen and read. */
4870         if (after(tp->copied_seq, ptr))
4871                 return;
4872
4873         /* Do not replay urg ptr.
4874          *
4875          * NOTE: interesting situation not covered by specs.
4876          * Misbehaving sender may send urg ptr, pointing to segment,
4877          * which we already have in ofo queue. We are not able to fetch
4878          * such data and will stay in TCP_URG_NOTYET until will be eaten
4879          * by recvmsg(). Seems, we are not obliged to handle such wicked
4880          * situations. But it is worth to think about possibility of some
4881          * DoSes using some hypothetical application level deadlock.
4882          */
4883         if (before(ptr, tp->rcv_nxt))
4884                 return;
4885
4886         /* Do we already have a newer (or duplicate) urgent pointer? */
4887         if (tp->urg_data && !after(ptr, tp->urg_seq))
4888                 return;
4889
4890         /* Tell the world about our new urgent pointer. */
4891         sk_send_sigurg(sk);
4892
4893         /* We may be adding urgent data when the last byte read was
4894          * urgent. To do this requires some care. We cannot just ignore
4895          * tp->copied_seq since we would read the last urgent byte again
4896          * as data, nor can we alter copied_seq until this data arrives
4897          * or we break the semantics of SIOCATMARK (and thus sockatmark())
4898          *
4899          * NOTE. Double Dutch. Rendering to plain English: author of comment
4900          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
4901          * and expect that both A and B disappear from stream. This is _wrong_.
4902          * Though this happens in BSD with high probability, this is occasional.
4903          * Any application relying on this is buggy. Note also, that fix "works"
4904          * only in this artificial test. Insert some normal data between A and B and we will
4905          * decline of BSD again. Verdict: it is better to remove to trap
4906          * buggy users.
4907          */
4908         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
4909             !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
4910                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
4911                 tp->copied_seq++;
4912                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
4913                         __skb_unlink(skb, &sk->sk_receive_queue);
4914                         __kfree_skb(skb);
4915                 }
4916         }
4917
4918         tp->urg_data = TCP_URG_NOTYET;
4919         tp->urg_seq = ptr;
4920
4921         /* Disable header prediction. */
4922         tp->pred_flags = 0;
4923 }
4924
4925 /* This is the 'fast' part of urgent handling. */
4926 static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
4927 {
4928         struct tcp_sock *tp = tcp_sk(sk);
4929
4930         /* Check if we get a new urgent pointer - normally not. */
4931         if (th->urg)
4932                 tcp_check_urg(sk, th);
4933
4934         /* Do we wait for any urgent data? - normally not... */
4935         if (tp->urg_data == TCP_URG_NOTYET) {
4936                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
4937                           th->syn;
4938
4939                 /* Is the urgent pointer pointing into this packet? */
4940                 if (ptr < skb->len) {
4941                         u8 tmp;
4942                         if (skb_copy_bits(skb, ptr, &tmp, 1))
4943                                 BUG();
4944                         tp->urg_data = TCP_URG_VALID | tmp;
4945                         if (!sock_flag(sk, SOCK_DEAD))
4946                                 sk->sk_data_ready(sk, 0);
4947                 }
4948         }
4949 }
4950
4951 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
4952 {
4953         struct tcp_sock *tp = tcp_sk(sk);
4954         int chunk = skb->len - hlen;
4955         int err;
4956
4957         local_bh_enable();
4958         if (skb_csum_unnecessary(skb))
4959                 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
4960         else
4961                 err = skb_copy_and_csum_datagram_iovec(skb, hlen,
4962                                                        tp->ucopy.iov);
4963
4964         if (!err) {
4965                 tp->ucopy.len -= chunk;
4966                 tp->copied_seq += chunk;
4967                 tcp_rcv_space_adjust(sk);
4968         }
4969
4970         local_bh_disable();
4971         return err;
4972 }
4973
4974 static __sum16 __tcp_checksum_complete_user(struct sock *sk,
4975                                             struct sk_buff *skb)
4976 {
4977         __sum16 result;
4978
4979         if (sock_owned_by_user(sk)) {
4980                 local_bh_enable();
4981                 result = __tcp_checksum_complete(skb);
4982                 local_bh_disable();
4983         } else {
4984                 result = __tcp_checksum_complete(skb);
4985         }
4986         return result;
4987 }
4988
4989 static inline int tcp_checksum_complete_user(struct sock *sk,
4990                                              struct sk_buff *skb)
4991 {
4992         return !skb_csum_unnecessary(skb) &&
4993                __tcp_checksum_complete_user(sk, skb);
4994 }
4995
4996 #ifdef CONFIG_NET_DMA
4997 static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb,
4998                                   int hlen)
4999 {
5000         struct tcp_sock *tp = tcp_sk(sk);
5001         int chunk = skb->len - hlen;
5002         int dma_cookie;
5003         int copied_early = 0;
5004
5005         if (tp->ucopy.wakeup)
5006                 return 0;
5007
5008         if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
5009                 tp->ucopy.dma_chan = dma_find_channel(DMA_MEMCPY);
5010
5011         if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
5012
5013                 dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
5014                                                          skb, hlen,
5015                                                          tp->ucopy.iov, chunk,
5016                                                          tp->ucopy.pinned_list);
5017
5018                 if (dma_cookie < 0)
5019                         goto out;
5020
5021                 tp->ucopy.dma_cookie = dma_cookie;
5022                 copied_early = 1;
5023
5024                 tp->ucopy.len -= chunk;
5025                 tp->copied_seq += chunk;
5026                 tcp_rcv_space_adjust(sk);
5027
5028                 if ((tp->ucopy.len == 0) ||
5029                     (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) ||
5030                     (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
5031                         tp->ucopy.wakeup = 1;
5032                         sk->sk_data_ready(sk, 0);
5033                 }
5034         } else if (chunk > 0) {
5035                 tp->ucopy.wakeup = 1;
5036                 sk->sk_data_ready(sk, 0);
5037         }
5038 out:
5039         return copied_early;
5040 }
5041 #endif /* CONFIG_NET_DMA */
5042
5043 /* Does PAWS and seqno based validation of an incoming segment, flags will
5044  * play significant role here.
5045  */
5046 static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5047                               struct tcphdr *th, int syn_inerr)
5048 {
5049         struct tcp_sock *tp = tcp_sk(sk);
5050
5051         /* RFC1323: H1. Apply PAWS check first. */
5052         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
5053             tcp_paws_discard(sk, skb)) {
5054                 if (!th->rst) {
5055                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5056                         tcp_send_dupack(sk, skb);
5057                         goto discard;
5058                 }
5059                 /* Reset is accepted even if it did not pass PAWS. */
5060         }
5061
5062         /* Step 1: check sequence number */
5063         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5064                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
5065                  * (RST) segments are validated by checking their SEQ-fields."
5066                  * And page 69: "If an incoming segment is not acceptable,
5067                  * an acknowledgment should be sent in reply (unless the RST
5068                  * bit is set, if so drop the segment and return)".
5069                  */
5070                 if (!th->rst)
5071                         tcp_send_dupack(sk, skb);
5072                 goto discard;
5073         }
5074
5075         /* Step 2: check RST bit */
5076         if (th->rst) {
5077                 tcp_reset(sk);
5078                 goto discard;
5079         }
5080
5081         /* ts_recent update must be made after we are sure that the packet
5082          * is in window.
5083          */
5084         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
5085
5086         /* step 3: check security and precedence [ignored] */
5087
5088         /* step 4: Check for a SYN in window. */
5089         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
5090                 if (syn_inerr)
5091                         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5092                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONSYN);
5093                 tcp_reset(sk);
5094                 return -1;
5095         }
5096
5097         return 1;
5098
5099 discard:
5100         __kfree_skb(skb);
5101         return 0;
5102 }
5103
5104 /*
5105  *      TCP receive function for the ESTABLISHED state.
5106  *
5107  *      It is split into a fast path and a slow path. The fast path is
5108  *      disabled when:
5109  *      - A zero window was announced from us - zero window probing
5110  *        is only handled properly in the slow path.
5111  *      - Out of order segments arrived.
5112  *      - Urgent data is expected.
5113  *      - There is no buffer space left
5114  *      - Unexpected TCP flags/window values/header lengths are received
5115  *        (detected by checking the TCP header against pred_flags)
5116  *      - Data is sent in both directions. Fast path only supports pure senders
5117  *        or pure receivers (this means either the sequence number or the ack
5118  *        value must stay constant)
5119  *      - Unexpected TCP option.
5120  *
5121  *      When these conditions are not satisfied it drops into a standard
5122  *      receive procedure patterned after RFC793 to handle all cases.
5123  *      The first three cases are guaranteed by proper pred_flags setting,
5124  *      the rest is checked inline. Fast processing is turned on in
5125  *      tcp_data_queue when everything is OK.
5126  */
5127 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
5128                         struct tcphdr *th, unsigned len)
5129 {
5130         struct tcp_sock *tp = tcp_sk(sk);
5131         int res;
5132
5133         /*
5134          *      Header prediction.
5135          *      The code loosely follows the one in the famous
5136          *      "30 instruction TCP receive" Van Jacobson mail.
5137          *
5138          *      Van's trick is to deposit buffers into socket queue
5139          *      on a device interrupt, to call tcp_recv function
5140          *      on the receive process context and checksum and copy
5141          *      the buffer to user space. smart...
5142          *
5143          *      Our current scheme is not silly either but we take the
5144          *      extra cost of the net_bh soft interrupt processing...
5145          *      We do checksum and copy also but from device to kernel.
5146          */
5147
5148         tp->rx_opt.saw_tstamp = 0;
5149
5150         /*      pred_flags is 0xS?10 << 16 + snd_wnd
5151          *      if header_prediction is to be made
5152          *      'S' will always be tp->tcp_header_len >> 2
5153          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
5154          *  turn it off (when there are holes in the receive
5155          *       space for instance)
5156          *      PSH flag is ignored.
5157          */
5158
5159         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5160             TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
5161                 int tcp_header_len = tp->tcp_header_len;
5162
5163                 /* Timestamp header prediction: tcp_header_len
5164                  * is automatically equal to th->doff*4 due to pred_flags
5165                  * match.
5166                  */
5167
5168                 /* Check timestamp */
5169                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5170                         /* No? Slow path! */
5171                         if (!tcp_parse_aligned_timestamp(tp, th))
5172                                 goto slow_path;
5173
5174                         /* If PAWS failed, check it more carefully in slow path */
5175                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5176                                 goto slow_path;
5177
5178                         /* DO NOT update ts_recent here, if checksum fails
5179                          * and timestamp was corrupted part, it will result
5180                          * in a hung connection since we will drop all
5181                          * future packets due to the PAWS test.
5182                          */
5183                 }
5184
5185                 if (len <= tcp_header_len) {
5186                         /* Bulk data transfer: sender */
5187                         if (len == tcp_header_len) {
5188                                 /* Predicted packet is in window by definition.
5189                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5190                                  * Hence, check seq<=rcv_wup reduces to:
5191                                  */
5192                                 if (tcp_header_len ==
5193                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5194                                     tp->rcv_nxt == tp->rcv_wup)
5195                                         tcp_store_ts_recent(tp);
5196
5197                                 /* We know that such packets are checksummed
5198                                  * on entry.
5199                                  */
5200                                 tcp_ack(sk, skb, 0);
5201                                 __kfree_skb(skb);
5202                                 tcp_data_snd_check(sk);
5203                                 return 0;
5204                         } else { /* Header too small */
5205                                 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5206                                 goto discard;
5207                         }
5208                 } else {
5209                         int eaten = 0;
5210                         int copied_early = 0;
5211
5212                         if (tp->copied_seq == tp->rcv_nxt &&
5213                             len - tcp_header_len <= tp->ucopy.len) {
5214 #ifdef CONFIG_NET_DMA
5215                                 if (tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
5216                                         copied_early = 1;
5217                                         eaten = 1;
5218                                 }
5219 #endif
5220                                 if (tp->ucopy.task == current &&
5221                                     sock_owned_by_user(sk) && !copied_early) {
5222                                         __set_current_state(TASK_RUNNING);
5223
5224                                         if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
5225                                                 eaten = 1;
5226                                 }
5227                                 if (eaten) {
5228                                         /* Predicted packet is in window by definition.
5229                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5230                                          * Hence, check seq<=rcv_wup reduces to:
5231                                          */
5232                                         if (tcp_header_len ==
5233                                             (sizeof(struct tcphdr) +
5234                                              TCPOLEN_TSTAMP_ALIGNED) &&
5235                                             tp->rcv_nxt == tp->rcv_wup)
5236                                                 tcp_store_ts_recent(tp);
5237
5238                                         tcp_rcv_rtt_measure_ts(sk, skb);
5239
5240                                         __skb_pull(skb, tcp_header_len);
5241                                         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
5242                                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER);
5243                                 }
5244                                 if (copied_early)
5245                                         tcp_cleanup_rbuf(sk, skb->len);
5246                         }
5247                         if (!eaten) {
5248                                 if (tcp_checksum_complete_user(sk, skb))
5249                                         goto csum_error;
5250
5251                                 /* Predicted packet is in window by definition.
5252                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5253                                  * Hence, check seq<=rcv_wup reduces to:
5254                                  */
5255                                 if (tcp_header_len ==
5256                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5257                                     tp->rcv_nxt == tp->rcv_wup)
5258                                         tcp_store_ts_recent(tp);
5259
5260                                 tcp_rcv_rtt_measure_ts(sk, skb);
5261
5262                                 if ((int)skb->truesize > sk->sk_forward_alloc)
5263                                         goto step5;
5264
5265                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
5266
5267                                 /* Bulk data transfer: receiver */
5268                                 __skb_pull(skb, tcp_header_len);
5269                                 __skb_queue_tail(&sk->sk_receive_queue, skb);
5270                                 skb_set_owner_r(skb, sk);
5271                                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
5272                         }
5273
5274                         tcp_event_data_recv(sk, skb);
5275
5276                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5277                                 /* Well, only one small jumplet in fast path... */
5278                                 tcp_ack(sk, skb, FLAG_DATA);
5279                                 tcp_data_snd_check(sk);
5280                                 if (!inet_csk_ack_scheduled(sk))
5281                                         goto no_ack;
5282                         }
5283
5284                         if (!copied_early || tp->rcv_nxt != tp->rcv_wup)
5285                                 __tcp_ack_snd_check(sk, 0);
5286 no_ack:
5287 #ifdef CONFIG_NET_DMA
5288                         if (copied_early)
5289                                 __skb_queue_tail(&sk->sk_async_wait_queue, skb);
5290                         else
5291 #endif
5292                         if (eaten)
5293                                 __kfree_skb(skb);
5294                         else
5295                                 sk->sk_data_ready(sk, 0);
5296                         return 0;
5297                 }
5298         }
5299
5300 slow_path:
5301         if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
5302                 goto csum_error;
5303
5304         /*
5305          *      Standard slow path.
5306          */
5307
5308         res = tcp_validate_incoming(sk, skb, th, 1);
5309         if (res <= 0)
5310                 return -res;
5311
5312 step5:
5313         if (th->ack)
5314                 tcp_ack(sk, skb, FLAG_SLOWPATH);
5315
5316         tcp_rcv_rtt_measure_ts(sk, skb);
5317
5318         /* Process urgent data. */
5319         tcp_urg(sk, skb, th);
5320
5321         /* step 7: process the segment text */
5322         tcp_data_queue(sk, skb);
5323
5324         tcp_data_snd_check(sk);
5325         tcp_ack_snd_check(sk);
5326         return 0;
5327
5328 csum_error:
5329         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5330
5331 discard:
5332         __kfree_skb(skb);
5333         return 0;
5334 }
5335
5336 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
5337                                          struct tcphdr *th, unsigned len)
5338 {
5339         struct tcp_sock *tp = tcp_sk(sk);
5340         struct inet_connection_sock *icsk = inet_csk(sk);
5341         int saved_clamp = tp->rx_opt.mss_clamp;
5342
5343         tcp_parse_options(skb, &tp->rx_opt, 0);
5344
5345         if (th->ack) {
5346                 /* rfc793:
5347                  * "If the state is SYN-SENT then
5348                  *    first check the ACK bit
5349                  *      If the ACK bit is set
5350                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
5351                  *        a reset (unless the RST bit is set, if so drop
5352                  *        the segment and return)"
5353                  *
5354                  *  We do not send data with SYN, so that RFC-correct
5355                  *  test reduces to:
5356                  */
5357                 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
5358                         goto reset_and_undo;
5359
5360                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5361                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
5362                              tcp_time_stamp)) {
5363                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED);
5364                         goto reset_and_undo;
5365                 }
5366
5367                 /* Now ACK is acceptable.
5368                  *
5369                  * "If the RST bit is set
5370                  *    If the ACK was acceptable then signal the user "error:
5371                  *    connection reset", drop the segment, enter CLOSED state,
5372                  *    delete TCB, and return."
5373                  */
5374
5375                 if (th->rst) {
5376                         tcp_reset(sk);
5377                         goto discard;
5378                 }
5379
5380                 /* rfc793:
5381                  *   "fifth, if neither of the SYN or RST bits is set then
5382                  *    drop the segment and return."
5383                  *
5384                  *    See note below!
5385                  *                                        --ANK(990513)
5386                  */
5387                 if (!th->syn)
5388                         goto discard_and_undo;
5389
5390                 /* rfc793:
5391                  *   "If the SYN bit is on ...
5392                  *    are acceptable then ...
5393                  *    (our SYN has been ACKed), change the connection
5394                  *    state to ESTABLISHED..."
5395                  */
5396
5397                 TCP_ECN_rcv_synack(tp, th);
5398
5399                 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
5400                 tcp_ack(sk, skb, FLAG_SLOWPATH);
5401
5402                 /* Ok.. it's good. Set up sequence numbers and
5403                  * move to established.
5404                  */
5405                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5406                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5407
5408                 /* RFC1323: The window in SYN & SYN/ACK segments is
5409                  * never scaled.
5410                  */
5411                 tp->snd_wnd = ntohs(th->window);
5412                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq);
5413
5414                 if (!tp->rx_opt.wscale_ok) {
5415                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
5416                         tp->window_clamp = min(tp->window_clamp, 65535U);
5417                 }
5418
5419                 if (tp->rx_opt.saw_tstamp) {
5420                         tp->rx_opt.tstamp_ok       = 1;
5421                         tp->tcp_header_len =
5422                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5423                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
5424                         tcp_store_ts_recent(tp);
5425                 } else {
5426                         tp->tcp_header_len = sizeof(struct tcphdr);
5427                 }
5428
5429                 if (tcp_is_sack(tp) && sysctl_tcp_fack)
5430                         tcp_enable_fack(tp);
5431
5432                 tcp_mtup_init(sk);
5433                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5434                 tcp_initialize_rcv_mss(sk);
5435
5436                 /* Remember, tcp_poll() does not lock socket!
5437                  * Change state from SYN-SENT only after copied_seq
5438                  * is initialized. */
5439                 tp->copied_seq = tp->rcv_nxt;
5440                 smp_mb();
5441                 tcp_set_state(sk, TCP_ESTABLISHED);
5442
5443                 security_inet_conn_established(sk, skb);
5444
5445                 /* Make sure socket is routed, for correct metrics.  */
5446                 icsk->icsk_af_ops->rebuild_header(sk);
5447
5448                 tcp_init_metrics(sk);
5449
5450                 tcp_init_congestion_control(sk);
5451
5452                 /* Prevent spurious tcp_cwnd_restart() on first data
5453                  * packet.
5454                  */
5455                 tp->lsndtime = tcp_time_stamp;
5456
5457                 tcp_init_buffer_space(sk);
5458
5459                 if (sock_flag(sk, SOCK_KEEPOPEN))
5460                         inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
5461
5462                 if (!tp->rx_opt.snd_wscale)
5463                         __tcp_fast_path_on(tp, tp->snd_wnd);
5464                 else
5465                         tp->pred_flags = 0;
5466
5467                 if (!sock_flag(sk, SOCK_DEAD)) {
5468                         sk->sk_state_change(sk);
5469                         sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5470                 }
5471
5472                 if (sk->sk_write_pending ||
5473                     icsk->icsk_accept_queue.rskq_defer_accept ||
5474                     icsk->icsk_ack.pingpong) {
5475                         /* Save one ACK. Data will be ready after
5476                          * several ticks, if write_pending is set.
5477                          *
5478                          * It may be deleted, but with this feature tcpdumps
5479                          * look so _wonderfully_ clever, that I was not able
5480                          * to stand against the temptation 8)     --ANK
5481                          */
5482                         inet_csk_schedule_ack(sk);
5483                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
5484                         icsk->icsk_ack.ato       = TCP_ATO_MIN;
5485                         tcp_incr_quickack(sk);
5486                         tcp_enter_quickack_mode(sk);
5487                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
5488                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
5489
5490 discard:
5491                         __kfree_skb(skb);
5492                         return 0;
5493                 } else {
5494                         tcp_send_ack(sk);
5495                 }
5496                 return -1;
5497         }
5498
5499         /* No ACK in the segment */
5500
5501         if (th->rst) {
5502                 /* rfc793:
5503                  * "If the RST bit is set
5504                  *
5505                  *      Otherwise (no ACK) drop the segment and return."
5506                  */
5507
5508                 goto discard_and_undo;
5509         }
5510
5511         /* PAWS check. */
5512         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
5513             tcp_paws_check(&tp->rx_opt, 0))
5514                 goto discard_and_undo;
5515
5516         if (th->syn) {
5517                 /* We see SYN without ACK. It is attempt of
5518                  * simultaneous connect with crossed SYNs.
5519                  * Particularly, it can be connect to self.
5520                  */
5521                 tcp_set_state(sk, TCP_SYN_RECV);
5522
5523                 if (tp->rx_opt.saw_tstamp) {
5524                         tp->rx_opt.tstamp_ok = 1;
5525                         tcp_store_ts_recent(tp);
5526                         tp->tcp_header_len =
5527                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5528                 } else {
5529                         tp->tcp_header_len = sizeof(struct tcphdr);
5530                 }
5531
5532                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5533                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5534
5535                 /* RFC1323: The window in SYN & SYN/ACK segments is
5536                  * never scaled.
5537                  */
5538                 tp->snd_wnd    = ntohs(th->window);
5539                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
5540                 tp->max_window = tp->snd_wnd;
5541
5542                 TCP_ECN_rcv_syn(tp, th);
5543
5544                 tcp_mtup_init(sk);
5545                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5546                 tcp_initialize_rcv_mss(sk);
5547
5548                 tcp_send_synack(sk);
5549 #if 0
5550                 /* Note, we could accept data and URG from this segment.
5551                  * There are no obstacles to make this.
5552                  *
5553                  * However, if we ignore data in ACKless segments sometimes,
5554                  * we have no reasons to accept it sometimes.
5555                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
5556                  * is not flawless. So, discard packet for sanity.
5557                  * Uncomment this return to process the data.
5558                  */
5559                 return -1;
5560 #else
5561                 goto discard;
5562 #endif
5563         }
5564         /* "fifth, if neither of the SYN or RST bits is set then
5565          * drop the segment and return."
5566          */
5567
5568 discard_and_undo:
5569         tcp_clear_options(&tp->rx_opt);
5570         tp->rx_opt.mss_clamp = saved_clamp;
5571         goto discard;
5572
5573 reset_and_undo:
5574         tcp_clear_options(&tp->rx_opt);
5575         tp->rx_opt.mss_clamp = saved_clamp;
5576         return 1;
5577 }
5578
5579 /*
5580  *      This function implements the receiving procedure of RFC 793 for
5581  *      all states except ESTABLISHED and TIME_WAIT.
5582  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
5583  *      address independent.
5584  */
5585
5586 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
5587                           struct tcphdr *th, unsigned len)
5588 {
5589         struct tcp_sock *tp = tcp_sk(sk);
5590         struct inet_connection_sock *icsk = inet_csk(sk);
5591         int queued = 0;
5592         int res;
5593
5594         tp->rx_opt.saw_tstamp = 0;
5595
5596         switch (sk->sk_state) {
5597         case TCP_CLOSE:
5598                 goto discard;
5599
5600         case TCP_LISTEN:
5601                 if (th->ack)
5602                         return 1;
5603
5604                 if (th->rst)
5605                         goto discard;
5606
5607                 if (th->syn) {
5608                         if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
5609                                 return 1;
5610
5611                         /* Now we have several options: In theory there is
5612                          * nothing else in the frame. KA9Q has an option to
5613                          * send data with the syn, BSD accepts data with the
5614                          * syn up to the [to be] advertised window and
5615                          * Solaris 2.1 gives you a protocol error. For now
5616                          * we just ignore it, that fits the spec precisely
5617                          * and avoids incompatibilities. It would be nice in
5618                          * future to drop through and process the data.
5619                          *
5620                          * Now that TTCP is starting to be used we ought to
5621                          * queue this data.
5622                          * But, this leaves one open to an easy denial of
5623                          * service attack, and SYN cookies can't defend
5624                          * against this problem. So, we drop the data
5625                          * in the interest of security over speed unless
5626                          * it's still in use.
5627                          */
5628                         kfree_skb(skb);
5629                         return 0;
5630                 }
5631                 goto discard;
5632
5633         case TCP_SYN_SENT:
5634                 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
5635                 if (queued >= 0)
5636                         return queued;
5637
5638                 /* Do step6 onward by hand. */
5639                 tcp_urg(sk, skb, th);
5640                 __kfree_skb(skb);
5641                 tcp_data_snd_check(sk);
5642                 return 0;
5643         }
5644
5645         res = tcp_validate_incoming(sk, skb, th, 0);
5646         if (res <= 0)
5647                 return -res;
5648
5649         /* step 5: check the ACK field */
5650         if (th->ack) {
5651                 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH);
5652
5653                 switch (sk->sk_state) {
5654                 case TCP_SYN_RECV:
5655                         if (acceptable) {
5656                                 tp->copied_seq = tp->rcv_nxt;
5657                                 smp_mb();
5658                                 tcp_set_state(sk, TCP_ESTABLISHED);
5659                                 sk->sk_state_change(sk);
5660
5661                                 /* Note, that this wakeup is only for marginal
5662                                  * crossed SYN case. Passively open sockets
5663                                  * are not waked up, because sk->sk_sleep ==
5664                                  * NULL and sk->sk_socket == NULL.
5665                                  */
5666                                 if (sk->sk_socket)
5667                                         sk_wake_async(sk,
5668                                                       SOCK_WAKE_IO, POLL_OUT);
5669
5670                                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5671                                 tp->snd_wnd = ntohs(th->window) <<
5672                                               tp->rx_opt.snd_wscale;
5673                                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq,
5674                                             TCP_SKB_CB(skb)->seq);
5675
5676                                 /* tcp_ack considers this ACK as duplicate
5677                                  * and does not calculate rtt.
5678                                  * Fix it at least with timestamps.
5679                                  */
5680                                 if (tp->rx_opt.saw_tstamp &&
5681                                     tp->rx_opt.rcv_tsecr && !tp->srtt)
5682                                         tcp_ack_saw_tstamp(sk, 0);
5683
5684                                 if (tp->rx_opt.tstamp_ok)
5685                                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5686
5687                                 /* Make sure socket is routed, for
5688                                  * correct metrics.
5689                                  */
5690                                 icsk->icsk_af_ops->rebuild_header(sk);
5691
5692                                 tcp_init_metrics(sk);
5693
5694                                 tcp_init_congestion_control(sk);
5695
5696                                 /* Prevent spurious tcp_cwnd_restart() on
5697                                  * first data packet.
5698                                  */
5699                                 tp->lsndtime = tcp_time_stamp;
5700
5701                                 tcp_mtup_init(sk);
5702                                 tcp_initialize_rcv_mss(sk);
5703                                 tcp_init_buffer_space(sk);
5704                                 tcp_fast_path_on(tp);
5705                         } else {
5706                                 return 1;
5707                         }
5708                         break;
5709
5710                 case TCP_FIN_WAIT1:
5711                         if (tp->snd_una == tp->write_seq) {
5712                                 tcp_set_state(sk, TCP_FIN_WAIT2);
5713                                 sk->sk_shutdown |= SEND_SHUTDOWN;
5714                                 dst_confirm(sk->sk_dst_cache);
5715
5716                                 if (!sock_flag(sk, SOCK_DEAD))
5717                                         /* Wake up lingering close() */
5718                                         sk->sk_state_change(sk);
5719                                 else {
5720                                         int tmo;
5721
5722                                         if (tp->linger2 < 0 ||
5723                                             (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5724                                              after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
5725                                                 tcp_done(sk);
5726                                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5727                                                 return 1;
5728                                         }
5729
5730                                         tmo = tcp_fin_time(sk);
5731                                         if (tmo > TCP_TIMEWAIT_LEN) {
5732                                                 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
5733                                         } else if (th->fin || sock_owned_by_user(sk)) {
5734                                                 /* Bad case. We could lose such FIN otherwise.
5735                                                  * It is not a big problem, but it looks confusing
5736                                                  * and not so rare event. We still can lose it now,
5737                                                  * if it spins in bh_lock_sock(), but it is really
5738                                                  * marginal case.
5739                                                  */
5740                                                 inet_csk_reset_keepalive_timer(sk, tmo);
5741                                         } else {
5742                                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
5743                                                 goto discard;
5744                                         }
5745                                 }
5746                         }
5747                         break;
5748
5749                 case TCP_CLOSING:
5750                         if (tp->snd_una == tp->write_seq) {
5751                                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
5752                                 goto discard;
5753                         }
5754                         break;
5755
5756                 case TCP_LAST_ACK:
5757                         if (tp->snd_una == tp->write_seq) {
5758                                 tcp_update_metrics(sk);
5759                                 tcp_done(sk);
5760                                 goto discard;
5761                         }
5762                         break;
5763                 }
5764         } else
5765                 goto discard;
5766
5767         /* step 6: check the URG bit */
5768         tcp_urg(sk, skb, th);
5769
5770         /* step 7: process the segment text */
5771         switch (sk->sk_state) {
5772         case TCP_CLOSE_WAIT:
5773         case TCP_CLOSING:
5774         case TCP_LAST_ACK:
5775                 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
5776                         break;
5777         case TCP_FIN_WAIT1:
5778         case TCP_FIN_WAIT2:
5779                 /* RFC 793 says to queue data in these states,
5780                  * RFC 1122 says we MUST send a reset.
5781                  * BSD 4.4 also does reset.
5782                  */
5783                 if (sk->sk_shutdown & RCV_SHUTDOWN) {
5784                         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5785                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
5786                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5787                                 tcp_reset(sk);
5788                                 return 1;
5789                         }
5790                 }
5791                 /* Fall through */
5792         case TCP_ESTABLISHED:
5793                 tcp_data_queue(sk, skb);
5794                 queued = 1;
5795                 break;
5796         }
5797
5798         /* tcp_data could move socket to TIME-WAIT */
5799         if (sk->sk_state != TCP_CLOSE) {
5800                 tcp_data_snd_check(sk);
5801                 tcp_ack_snd_check(sk);
5802         }
5803
5804         if (!queued) {
5805 discard:
5806                 __kfree_skb(skb);
5807         }
5808         return 0;
5809 }
5810
5811 EXPORT_SYMBOL(sysctl_tcp_ecn);
5812 EXPORT_SYMBOL(sysctl_tcp_reordering);
5813 EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
5814 EXPORT_SYMBOL(tcp_parse_options);
5815 #ifdef CONFIG_TCP_MD5SIG
5816 EXPORT_SYMBOL(tcp_parse_md5sig_option);
5817 #endif
5818 EXPORT_SYMBOL(tcp_rcv_established);
5819 EXPORT_SYMBOL(tcp_rcv_state_process);
5820 EXPORT_SYMBOL(tcp_initialize_rcv_mss);