net/ipv4/tcp_timer.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 #include <linux/module.h>
  22 #include <net/tcp.h>
  23
  24 int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES;
  25 int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES;
  26 int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME;
  27 int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;
  28 int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
  29 int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
  30 int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
  31 int sysctl_tcp_orphan_retries __read_mostly;
  32
  33 static void tcp_write_timer(unsigned long);
  34 static void tcp_delack_timer(unsigned long);
  35 static void tcp_keepalive_timer (unsigned long data);
  36
  37 void tcp_init_xmit_timers(struct sock *sk)
  38 {
  39         inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
  40                                   &tcp_keepalive_timer);
  41 }
  42
  43 EXPORT_SYMBOL(tcp_init_xmit_timers);
  44
  45 static void tcp_write_err(struct sock *sk)
  46 {
  47         sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
  48         sk->sk_error_report(sk);
  49
  50         tcp_done(sk);
  51         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
  52 }
  53
  54 /* Do not allow orphaned sockets to eat all our resources.
  55  * This is direct violation of TCP specs, but it is required
  56  * to prevent DoS attacks. It is called when a retransmission timeout
  57  * or zero probe timeout occurs on orphaned socket.
  58  *
  59  * Criteria is still not confirmed experimentally and may change.
  60  * We kill the socket, if:
  61  * 1. If number of orphaned sockets exceeds an administratively configured
  62  *    limit.
  63  * 2. If we have strong memory pressure.
  64  */
  65 static int tcp_out_of_resources(struct sock *sk, int do_reset)
  66 {
  67         struct tcp_sock *tp = tcp_sk(sk);
  68         int orphans = percpu_counter_read_positive(&tcp_orphan_count);
  69
  70         /* If peer does not open window for long time, or did not transmit
  71          * anything for long time, penalize it. */
  72         if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
  73                 orphans <<= 1;
  74
  75         /* If some dubious ICMP arrived, penalize even more. */
  76         if (sk->sk_err_soft)
  77                 orphans <<= 1;
  78
  79         if (tcp_too_many_orphans(sk, orphans)) {
  80                 if (net_ratelimit())
  81                         printk(KERN_INFO "Out of socket memory\n");
  82
  83                 /* Catch exceptional cases, when connection requires reset.
  84                  *      1. Last segment was sent recently. */
  85                 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
  86                     /*  2. Window is closed. */
  87                     (!tp->snd_wnd && !tp->packets_out))
  88                         do_reset = 1;
  89                 if (do_reset)
  90                         tcp_send_active_reset(sk, GFP_ATOMIC);
  91                 tcp_done(sk);
  92                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
  93                 return 1;
  94         }
  95         return 0;
  96 }
  97
  98 /* Calculate maximal number or retries on an orphaned socket. */
  99 static int tcp_orphan_retries(struct sock *sk, int alive)
 100 {
 101         int retries = sysctl_tcp_orphan_retries; /* May be zero. */
 102
 103         /* We know from an ICMP that something is wrong. */
 104         if (sk->sk_err_soft && !alive)
 105                 retries = 0;
 106
 107         /* However, if socket sent something recently, select some safe
 108          * number of retries. 8 corresponds to >100 seconds with minimal
 109          * RTO of 200msec. */
 110         if (retries == 0 && alive)
 111                 retries = 8;
 112         return retries;
 113 }
 114
 115 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 116 {
 117         /* Black hole detection */
 118         if (sysctl_tcp_mtu_probing) {
 119                 if (!icsk->icsk_mtup.enabled) {
 120                         icsk->icsk_mtup.enabled = 1;
 121                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 122                 } else {
 123                         struct tcp_sock *tp = tcp_sk(sk);
 124                         int mss;
 125
 126                         mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 127                         mss = min(sysctl_tcp_base_mss, mss);
 128                         mss = max(mss, 68 - tp->tcp_header_len);
 129                         icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 130                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 131                 }
 132         }
 133 }
 134
 135 /* A write timeout has occurred. Process the after effects. */
 136 static int tcp_write_timeout(struct sock *sk)
 137 {
 138         struct inet_connection_sock *icsk = inet_csk(sk);
 139         int retry_until;
 140
 141         if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 142                 if (icsk->icsk_retransmits)
 143                         dst_negative_advice(&sk->sk_dst_cache);
 144                 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
 145         } else {
 146                 if (icsk->icsk_retransmits >= sysctl_tcp_retries1) {
 147                         /* Black hole detection */
 148                         tcp_mtu_probing(icsk, sk);
 149
 150                         dst_negative_advice(&sk->sk_dst_cache);
 151                 }
 152
 153                 retry_until = sysctl_tcp_retries2;
 154                 if (sock_flag(sk, SOCK_DEAD)) {
 155                         const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
 156
 157                         retry_until = tcp_orphan_retries(sk, alive);
 158
 159                         if (tcp_out_of_resources(sk, alive || icsk->icsk_retransmits < retry_until))
 160                                 return 1;
 161                 }
 162         }
 163
 164         if (icsk->icsk_retransmits >= retry_until) {
 165                 /* Has it gone just too far? */
 166                 tcp_write_err(sk);
 167                 return 1;
 168         }
 169         return 0;
 170 }
 171
 172 static void tcp_delack_timer(unsigned long data)
 173 {
 174         struct sock *sk = (struct sock *)data;
 175         struct tcp_sock *tp = tcp_sk(sk);
 176         struct inet_connection_sock *icsk = inet_csk(sk);
 177
 178         bh_lock_sock(sk);
 179         if (sock_owned_by_user(sk)) {
 180                 /* Try again later. */
 181                 icsk->icsk_ack.blocked = 1;
 182                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
 183                 sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);
 184                 goto out_unlock;
 185         }
 186
 187         sk_mem_reclaim_partial(sk);
 188
 189         if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 190                 goto out;
 191
 192         if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 193                 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 194                 goto out;
 195         }
 196         icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 197
 198         if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 199                 struct sk_buff *skb;
 200
 201                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
 202
 203                 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 204                         sk_backlog_rcv(sk, skb);
 205
 206                 tp->ucopy.memory = 0;
 207         }
 208
 209         if (inet_csk_ack_scheduled(sk)) {
 210                 if (!icsk->icsk_ack.pingpong) {
 211                         /* Delayed ACK missed: inflate ATO. */
 212                         icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 213                 } else {
 214                         /* Delayed ACK missed: leave pingpong mode and
 215                          * deflate ATO.
 216                          */
 217                         icsk->icsk_ack.pingpong = 0;
 218                         icsk->icsk_ack.ato      = TCP_ATO_MIN;
 219                 }
 220                 tcp_send_ack(sk);
 221                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
 222         }
 223         TCP_CHECK_TIMER(sk);
 224
 225 out:
 226         if (tcp_memory_pressure)
 227                 sk_mem_reclaim(sk);
 228 out_unlock:
 229         bh_unlock_sock(sk);
 230         sock_put(sk);
 231 }
 232
 233 static void tcp_probe_timer(struct sock *sk)
 234 {
 235         struct inet_connection_sock *icsk = inet_csk(sk);
 236         struct tcp_sock *tp = tcp_sk(sk);
 237         int max_probes;
 238
 239         if (tp->packets_out || !tcp_send_head(sk)) {
 240                 icsk->icsk_probes_out = 0;
 241                 return;
 242         }
 243
 244         /* *WARNING* RFC 1122 forbids this
 245          *
 246          * It doesn't AFAIK, because we kill the retransmit timer -AK
 247          *
 248          * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
 249          * this behaviour in Solaris down as a bug fix. [AC]
 250          *
 251          * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
 252          * even if they advertise zero window. Hence, connection is killed only
 253          * if we received no ACKs for normal connection timeout. It is not killed
 254          * only because window stays zero for some time, window may be zero
 255          * until armageddon and even later. We are in full accordance
 256          * with RFCs, only probe timer combines both retransmission timeout
 257          * and probe timeout in one bottle.                             --ANK
 258          */
 259         max_probes = sysctl_tcp_retries2;
 260
 261         if (sock_flag(sk, SOCK_DEAD)) {
 262                 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
 263
 264                 max_probes = tcp_orphan_retries(sk, alive);
 265
 266                 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
 267                         return;
 268         }
 269
 270         if (icsk->icsk_probes_out > max_probes) {
 271                 tcp_write_err(sk);
 272         } else {
 273                 /* Only send another probe if we didn't close things up. */
 274                 tcp_send_probe0(sk);
 275         }
 276 }
 277
 278 /*
 279  *      The TCP retransmit timer.
 280  */
 281
 282 static void tcp_retransmit_timer(struct sock *sk)
 283 {
 284         struct tcp_sock *tp = tcp_sk(sk);
 285         struct inet_connection_sock *icsk = inet_csk(sk);
 286
 287         if (!tp->packets_out)
 288                 goto out;
 289
 290         WARN_ON(tcp_write_queue_empty(sk));
 291
 292         if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 293             !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 294                 /* Receiver dastardly shrinks window. Our retransmits
 295                  * become zero probes, but we should not timeout this
 296                  * connection. If the socket is an orphan, time it out,
 297                  * we cannot allow such beasts to hang infinitely.
 298                  */
 299 #ifdef TCP_DEBUG
 300                 struct inet_sock *inet = inet_sk(sk);
 301                 if (sk->sk_family == AF_INET) {
 302                         LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 303                                &inet->daddr, ntohs(inet->dport),
 304                                inet->num, tp->snd_una, tp->snd_nxt);
 305                 }
 306 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
 307                 else if (sk->sk_family == AF_INET6) {
 308                         struct ipv6_pinfo *np = inet6_sk(sk);
 309                         LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 310                                &np->daddr, ntohs(inet->dport),
 311                                inet->num, tp->snd_una, tp->snd_nxt);
 312                 }
 313 #endif
 314 #endif
 315                 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
 316                         tcp_write_err(sk);
 317                         goto out;
 318                 }
 319                 tcp_enter_loss(sk, 0);
 320                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
 321                 __sk_dst_reset(sk);
 322                 goto out_reset_timer;
 323         }
 324
 325         if (tcp_write_timeout(sk))
 326                 goto out;
 327
 328         if (icsk->icsk_retransmits == 0) {
 329                 int mib_idx;
 330
 331                 if (icsk->icsk_ca_state == TCP_CA_Disorder) {
 332                         if (tcp_is_sack(tp))
 333                                 mib_idx = LINUX_MIB_TCPSACKFAILURES;
 334                         else
 335                                 mib_idx = LINUX_MIB_TCPRENOFAILURES;
 336                 } else if (icsk->icsk_ca_state == TCP_CA_Recovery) {
 337                         if (tcp_is_sack(tp))
 338                                 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
 339                         else
 340                                 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
 341                 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 342                         mib_idx = LINUX_MIB_TCPLOSSFAILURES;
 343                 } else {
 344                         mib_idx = LINUX_MIB_TCPTIMEOUTS;
 345                 }
 346                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
 347         }
 348
 349         if (tcp_use_frto(sk)) {
 350                 tcp_enter_frto(sk);
 351         } else {
 352                 tcp_enter_loss(sk, 0);
 353         }
 354
 355         if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
 356                 /* Retransmission failed because of local congestion,
 357                  * do not backoff.
 358                  */
 359                 if (!icsk->icsk_retransmits)
 360                         icsk->icsk_retransmits = 1;
 361                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 362                                           min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
 363                                           TCP_RTO_MAX);
 364                 goto out;
 365         }
 366
 367         /* Increase the timeout each time we retransmit.  Note that
 368          * we do not increase the rtt estimate.  rto is initialized
 369          * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 370          * that doubling rto each time is the least we can get away with.
 371          * In KA9Q, Karn uses this for the first few times, and then
 372          * goes to quadratic.  netBSD doubles, but only goes up to *64,
 373          * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 374          * defined in the protocol as the maximum possible RTT.  I guess
 375          * we'll have to use something other than TCP to talk to the
 376          * University of Mars.
 377          *
 378          * PAWS allows us longer timeouts and large windows, so once
 379          * implemented ftp to mars will work nicely. We will have to fix
 380          * the 120 second clamps though!
 381          */
 382         icsk->icsk_backoff++;
 383         icsk->icsk_retransmits++;
 384
 385 out_reset_timer:
 386         icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 387         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
 388         if (icsk->icsk_retransmits > sysctl_tcp_retries1)
 389                 __sk_dst_reset(sk);
 390
 391 out:;
 392 }
 393
 394 static void tcp_write_timer(unsigned long data)
 395 {
 396         struct sock *sk = (struct sock *)data;
 397         struct inet_connection_sock *icsk = inet_csk(sk);
 398         int event;
 399
 400         bh_lock_sock(sk);
 401         if (sock_owned_by_user(sk)) {
 402                 /* Try again later */
 403                 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));
 404                 goto out_unlock;
 405         }
 406
 407         if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
 408                 goto out;
 409
 410         if (time_after(icsk->icsk_timeout, jiffies)) {
 411                 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 412                 goto out;
 413         }
 414
 415         event = icsk->icsk_pending;
 416         icsk->icsk_pending = 0;
 417
 418         switch (event) {
 419         case ICSK_TIME_RETRANS:
 420                 tcp_retransmit_timer(sk);
 421                 break;
 422         case ICSK_TIME_PROBE0:
 423                 tcp_probe_timer(sk);
 424                 break;
 425         }
 426         TCP_CHECK_TIMER(sk);
 427
 428 out:
 429         sk_mem_reclaim(sk);
 430 out_unlock:
 431         bh_unlock_sock(sk);
 432         sock_put(sk);
 433 }
 434
 435 /*
 436  *      Timer for listening sockets
 437  */
 438
 439 static void tcp_synack_timer(struct sock *sk)
 440 {
 441         inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
 442                                    TCP_TIMEOUT_INIT, TCP_RTO_MAX);
 443 }
 444
 445 void tcp_set_keepalive(struct sock *sk, int val)
 446 {
 447         if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 448                 return;
 449
 450         if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 451                 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 452         else if (!val)
 453                 inet_csk_delete_keepalive_timer(sk);
 454 }
 455
 456
 457 static void tcp_keepalive_timer (unsigned long data)
 458 {
 459         struct sock *sk = (struct sock *) data;
 460         struct inet_connection_sock *icsk = inet_csk(sk);
 461         struct tcp_sock *tp = tcp_sk(sk);
 462         __u32 elapsed;
 463
 464         /* Only process if socket is not in use. */
 465         bh_lock_sock(sk);
 466         if (sock_owned_by_user(sk)) {
 467                 /* Try again later. */
 468                 inet_csk_reset_keepalive_timer (sk, HZ/20);
 469                 goto out;
 470         }
 471
 472         if (sk->sk_state == TCP_LISTEN) {
 473                 tcp_synack_timer(sk);
 474                 goto out;
 475         }
 476
 477         if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 478                 if (tp->linger2 >= 0) {
 479                         const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 480
 481                         if (tmo > 0) {
 482                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 483                                 goto out;
 484                         }
 485                 }
 486                 tcp_send_active_reset(sk, GFP_ATOMIC);
 487                 goto death;
 488         }
 489
 490         if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
 491                 goto out;
 492
 493         elapsed = keepalive_time_when(tp);
 494
 495         /* It is alive without keepalive 8) */
 496         if (tp->packets_out || tcp_send_head(sk))
 497                 goto resched;
 498
 499         elapsed = tcp_time_stamp - tp->rcv_tstamp;
 500
 501         if (elapsed >= keepalive_time_when(tp)) {
 502                 if ((!tp->keepalive_probes && icsk->icsk_probes_out >= sysctl_tcp_keepalive_probes) ||
 503                      (tp->keepalive_probes && icsk->icsk_probes_out >= tp->keepalive_probes)) {
 504                         tcp_send_active_reset(sk, GFP_ATOMIC);
 505                         tcp_write_err(sk);
 506                         goto out;
 507                 }
 508                 if (tcp_write_wakeup(sk) <= 0) {
 509                         icsk->icsk_probes_out++;
 510                         elapsed = keepalive_intvl_when(tp);
 511                 } else {
 512                         /* If keepalive was lost due to local congestion,
 513                          * try harder.
 514                          */
 515                         elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 516                 }
 517         } else {
 518                 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 519                 elapsed = keepalive_time_when(tp) - elapsed;
 520         }
 521
 522         TCP_CHECK_TIMER(sk);
 523         sk_mem_reclaim(sk);
 524
 525 resched:
 526         inet_csk_reset_keepalive_timer (sk, elapsed);
 527         goto out;
 528
 529 death:
 530         tcp_done(sk);
 531
 532 out:
 533         bh_unlock_sock(sk);
 534         sock_put(sk);
 535 }