net/dccp/input.c

   1 /*
   2  *  net/dccp/input.c
   3  *
   4  *  An implementation of the DCCP protocol
   5  *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
   6  *
   7  *      This program is free software; you can redistribute it and/or
   8  *      modify it under the terms of the GNU General Public License
   9  *      as published by the Free Software Foundation; either version
  10  *      2 of the License, or (at your option) any later version.
  11  */
  12
  13 #include <linux/config.h>
  14 #include <linux/dccp.h>
  15 #include <linux/skbuff.h>
  16
  17 #include <net/sock.h>
  18
  19 #include "ccid.h"
  20 #include "dccp.h"
  21
  22 static void dccp_fin(struct sock *sk, struct sk_buff *skb)
  23 {
  24         sk->sk_shutdown |= RCV_SHUTDOWN;
  25         sock_set_flag(sk, SOCK_DONE);
  26         __skb_pull(skb, dccp_hdr(skb)->dccph_doff * 4);
  27         __skb_queue_tail(&sk->sk_receive_queue, skb);
  28         skb_set_owner_r(skb, sk);
  29         sk->sk_data_ready(sk, 0);
  30 }
  31
  32 static void dccp_rcv_close(struct sock *sk, struct sk_buff *skb)
  33 {
  34         dccp_v4_send_reset(sk, DCCP_RESET_CODE_CLOSED);
  35         dccp_fin(sk, skb);
  36         dccp_set_state(sk, DCCP_CLOSED);
  37         sk_wake_async(sk, 1, POLL_HUP);
  38 }
  39
  40 static void dccp_rcv_closereq(struct sock *sk, struct sk_buff *skb)
  41 {
  42         /*
  43          *   Step 7: Check for unexpected packet types
  44          *      If (S.is_server and P.type == CloseReq)
  45          *        Send Sync packet acknowledging P.seqno
  46          *        Drop packet and return
  47          */
  48         if (dccp_sk(sk)->dccps_role != DCCP_ROLE_CLIENT) {
  49                 dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq, DCCP_PKT_SYNC);
  50                 return;
  51         }
  52
  53         dccp_set_state(sk, DCCP_CLOSING);
  54         dccp_send_close(sk, 0);
  55 }
  56
  57 static inline void dccp_event_ack_recv(struct sock *sk, struct sk_buff *skb)
  58 {
  59         struct dccp_sock *dp = dccp_sk(sk);
  60
  61         if (dp->dccps_options.dccpo_send_ack_vector)
  62                 dccp_ackpkts_check_rcv_ackno(dp->dccps_hc_rx_ackpkts, sk,
  63                                              DCCP_SKB_CB(skb)->dccpd_ack_seq);
  64 }
  65
  66 static int dccp_check_seqno(struct sock *sk, struct sk_buff *skb)
  67 {
  68         const struct dccp_hdr *dh = dccp_hdr(skb);
  69         struct dccp_sock *dp = dccp_sk(sk);
  70         u64 lswl, lawl;
  71
  72         /*
  73          *   Step 5: Prepare sequence numbers for Sync
  74          *     If P.type == Sync or P.type == SyncAck,
  75          *        If S.AWL <= P.ackno <= S.AWH and P.seqno >= S.SWL,
  76          *           / * P is valid, so update sequence number variables
  77          *               accordingly.  After this update, P will pass the tests
  78          *               in Step 6.  A SyncAck is generated if necessary in
  79          *               Step 15 * /
  80          *           Update S.GSR, S.SWL, S.SWH
  81          *        Otherwise,
  82          *           Drop packet and return
  83          */
  84         if (dh->dccph_type == DCCP_PKT_SYNC ||
  85             dh->dccph_type == DCCP_PKT_SYNCACK) {
  86                 if (between48(DCCP_SKB_CB(skb)->dccpd_ack_seq,
  87                               dp->dccps_awl, dp->dccps_awh) &&
  88                     !before48(DCCP_SKB_CB(skb)->dccpd_seq, dp->dccps_swl))
  89                         dccp_update_gsr(sk, DCCP_SKB_CB(skb)->dccpd_seq);
  90                 else
  91                         return -1;
  92         }
  93
  94         /*
  95          *   Step 6: Check sequence numbers
  96          *      Let LSWL = S.SWL and LAWL = S.AWL
  97          *      If P.type == CloseReq or P.type == Close or P.type == Reset,
  98          *        LSWL := S.GSR + 1, LAWL := S.GAR
  99          *      If LSWL <= P.seqno <= S.SWH
 100          *           and (P.ackno does not exist or LAWL <= P.ackno <= S.AWH),
 101          *        Update S.GSR, S.SWL, S.SWH
 102          *        If P.type != Sync,
 103          *           Update S.GAR
 104          *      Otherwise,
 105          *        Send Sync packet acknowledging P.seqno
 106          *        Drop packet and return
 107          */
 108         lswl = dp->dccps_swl;
 109         lawl = dp->dccps_awl;
 110
 111         if (dh->dccph_type == DCCP_PKT_CLOSEREQ ||
 112             dh->dccph_type == DCCP_PKT_CLOSE ||
 113             dh->dccph_type == DCCP_PKT_RESET) {
 114                 lswl = dp->dccps_gsr;
 115                 dccp_inc_seqno(&lswl);
 116                 lawl = dp->dccps_gar;
 117         }
 118
 119         if (between48(DCCP_SKB_CB(skb)->dccpd_seq, lswl, dp->dccps_swh) &&
 120             (DCCP_SKB_CB(skb)->dccpd_ack_seq == DCCP_PKT_WITHOUT_ACK_SEQ ||
 121              between48(DCCP_SKB_CB(skb)->dccpd_ack_seq,
 122                        lawl, dp->dccps_awh))) {
 123                 dccp_update_gsr(sk, DCCP_SKB_CB(skb)->dccpd_seq);
 124
 125                 if (dh->dccph_type != DCCP_PKT_SYNC &&
 126                     (DCCP_SKB_CB(skb)->dccpd_ack_seq !=
 127                      DCCP_PKT_WITHOUT_ACK_SEQ))
 128                         dp->dccps_gar = DCCP_SKB_CB(skb)->dccpd_ack_seq;
 129         } else {
 130                 LIMIT_NETDEBUG(KERN_WARNING "DCCP: Step 6 failed for %s packet, "
 131                                             "(LSWL(%llu) <= P.seqno(%llu) <= S.SWH(%llu)) and "
 132                                             "(P.ackno %s or LAWL(%llu) <= P.ackno(%llu) <= S.AWH(%llu), "
 133                                             "sending SYNC...\n",
 134                                dccp_packet_name(dh->dccph_type),
 135                                (unsigned long long) lswl,
 136                                (unsigned long long)
 137                                DCCP_SKB_CB(skb)->dccpd_seq,
 138                                (unsigned long long) dp->dccps_swh,
 139                                (DCCP_SKB_CB(skb)->dccpd_ack_seq ==
 140                                 DCCP_PKT_WITHOUT_ACK_SEQ) ? "doesn't exist" : "exists",
 141                                (unsigned long long) lawl,
 142                                (unsigned long long)
 143                                DCCP_SKB_CB(skb)->dccpd_ack_seq,
 144                                (unsigned long long) dp->dccps_awh);
 145                 dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq, DCCP_PKT_SYNC);
 146                 return -1;
 147         }
 148
 149         return 0;
 150 }
 151
 152 int dccp_rcv_established(struct sock *sk, struct sk_buff *skb,
 153                          const struct dccp_hdr *dh, const unsigned len)
 154 {
 155         struct dccp_sock *dp = dccp_sk(sk);
 156
 157         if (dccp_check_seqno(sk, skb))
 158                 goto discard;
 159
 160         if (dccp_parse_options(sk, skb))
 161                 goto discard;
 162
 163         if (DCCP_SKB_CB(skb)->dccpd_ack_seq != DCCP_PKT_WITHOUT_ACK_SEQ)
 164                 dccp_event_ack_recv(sk, skb);
 165
 166         /*
 167          * FIXME: check ECN to see if we should use
 168          * DCCP_ACKPKTS_STATE_ECN_MARKED
 169          */
 170         if (dp->dccps_options.dccpo_send_ack_vector) {
 171                 struct dccp_ackpkts *ap = dp->dccps_hc_rx_ackpkts;
 172
 173                 if (dccp_ackpkts_add(dp->dccps_hc_rx_ackpkts,
 174                                      DCCP_SKB_CB(skb)->dccpd_seq,
 175                                      DCCP_ACKPKTS_STATE_RECEIVED)) {
 176                         LIMIT_NETDEBUG(KERN_WARNING "DCCP: acknowledgeable "
 177                                                     "packets buffer full!\n");
 178                         ap->dccpap_ack_seqno = DCCP_MAX_SEQNO + 1;
 179                         inet_csk_schedule_ack(sk);
 180                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
 181                                                   TCP_DELACK_MIN,
 182                                                   DCCP_RTO_MAX);
 183                         goto discard;
 184                 }
 185
 186                 /*
 187                  * FIXME: this activation is probably wrong, have to study more
 188                  * TCP delack machinery and how it fits into DCCP draft, but
 189                  * for now it kinda "works" 8)
 190                  */
 191                 if (!inet_csk_ack_scheduled(sk)) {
 192                         inet_csk_schedule_ack(sk);
 193                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, 5 * HZ,
 194                                                   DCCP_RTO_MAX);
 195                 }
 196         }
 197
 198         ccid_hc_rx_packet_recv(dp->dccps_hc_rx_ccid, sk, skb);
 199         ccid_hc_tx_packet_recv(dp->dccps_hc_tx_ccid, sk, skb);
 200
 201         switch (dccp_hdr(skb)->dccph_type) {
 202         case DCCP_PKT_DATAACK:
 203         case DCCP_PKT_DATA:
 204                 /*
 205                  * FIXME: check if sk_receive_queue is full, schedule DATA_DROPPED
 206                  * option if it is.
 207                  */
 208                 __skb_pull(skb, dh->dccph_doff * 4);
 209                 __skb_queue_tail(&sk->sk_receive_queue, skb);
 210                 skb_set_owner_r(skb, sk);
 211                 sk->sk_data_ready(sk, 0);
 212                 return 0;
 213         case DCCP_PKT_ACK:
 214                 goto discard;
 215         case DCCP_PKT_RESET:
 216                 /*
 217                  *  Step 9: Process Reset
 218                  *      If P.type == Reset,
 219                  *              Tear down connection
 220                  *              S.state := TIMEWAIT
 221                  *              Set TIMEWAIT timer
 222                  *              Drop packet and return
 223                 */
 224                 dccp_fin(sk, skb);
 225                 dccp_time_wait(sk, DCCP_TIME_WAIT, 0);
 226                 return 0;
 227         case DCCP_PKT_CLOSEREQ:
 228                 dccp_rcv_closereq(sk, skb);
 229                 goto discard;
 230         case DCCP_PKT_CLOSE:
 231                 dccp_rcv_close(sk, skb);
 232                 return 0;
 233         case DCCP_PKT_REQUEST:
 234                 /* Step 7
 235                  *   or (S.is_server and P.type == Response)
 236                  *   or (S.is_client and P.type == Request)
 237                  *   or (S.state >= OPEN and P.type == Request
 238                  *      and P.seqno >= S.OSR)
 239                  *    or (S.state >= OPEN and P.type == Response
 240                  *      and P.seqno >= S.OSR)
 241                  *    or (S.state == RESPOND and P.type == Data),
 242                  *  Send Sync packet acknowledging P.seqno
 243                  *  Drop packet and return
 244                  */
 245                 if (dp->dccps_role != DCCP_ROLE_LISTEN)
 246                         goto send_sync;
 247                 goto check_seq;
 248         case DCCP_PKT_RESPONSE:
 249                 if (dp->dccps_role != DCCP_ROLE_CLIENT)
 250                         goto send_sync;
 251 check_seq:
 252                 if (!before48(DCCP_SKB_CB(skb)->dccpd_seq, dp->dccps_osr)) {
 253 send_sync:
 254                         dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq,
 255                                        DCCP_PKT_SYNC);
 256                 }
 257                 break;
 258         case DCCP_PKT_SYNC:
 259                 dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq,
 260                                DCCP_PKT_SYNCACK);
 261                 /*
 262                  * From the draft:
 263                  *
 264                  * As with DCCP-Ack packets, DCCP-Sync and DCCP-SyncAck packets
 265                  * MAY have non-zero-length application data areas, whose
 266                  * contents * receivers MUST ignore.
 267                  */
 268                 goto discard;
 269         }
 270
 271         DCCP_INC_STATS_BH(DCCP_MIB_INERRS);
 272 discard:
 273         __kfree_skb(skb);
 274         return 0;
 275 }
 276
 277 static int dccp_rcv_request_sent_state_process(struct sock *sk,
 278                                                struct sk_buff *skb,
 279                                                const struct dccp_hdr *dh,
 280                                                const unsigned len)
 281 {
 282         /*
 283          *  Step 4: Prepare sequence numbers in REQUEST
 284          *     If S.state == REQUEST,
 285          *        If (P.type == Response or P.type == Reset)
 286          *              and S.AWL <= P.ackno <= S.AWH,
 287          *           / * Set sequence number variables corresponding to the
 288          *              other endpoint, so P will pass the tests in Step 6 * /
 289          *           Set S.GSR, S.ISR, S.SWL, S.SWH
 290          *           / * Response processing continues in Step 10; Reset
 291          *              processing continues in Step 9 * /
 292         */
 293         if (dh->dccph_type == DCCP_PKT_RESPONSE) {
 294                 const struct inet_connection_sock *icsk = inet_csk(sk);
 295                 struct dccp_sock *dp = dccp_sk(sk);
 296
 297                 /* Stop the REQUEST timer */
 298                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
 299                 BUG_TRAP(sk->sk_send_head != NULL);
 300                 __kfree_skb(sk->sk_send_head);
 301                 sk->sk_send_head = NULL;
 302
 303                 if (!between48(DCCP_SKB_CB(skb)->dccpd_ack_seq,
 304                                dp->dccps_awl, dp->dccps_awh)) {
 305                         dccp_pr_debug("invalid ackno: S.AWL=%llu, "
 306                                       "P.ackno=%llu, S.AWH=%llu \n",
 307                                       (unsigned long long)dp->dccps_awl,
 308                            (unsigned long long)DCCP_SKB_CB(skb)->dccpd_ack_seq,
 309                                       (unsigned long long)dp->dccps_awh);
 310                         goto out_invalid_packet;
 311                 }
 312
 313                 dp->dccps_isr = DCCP_SKB_CB(skb)->dccpd_seq;
 314                 dccp_update_gsr(sk, dp->dccps_isr);
 315                 /*
 316                  * SWL and AWL are initially adjusted so that they are not less than
 317                  * the initial Sequence Numbers received and sent, respectively:
 318                  *      SWL := max(GSR + 1 - floor(W/4), ISR),
 319                  *      AWL := max(GSS - W' + 1, ISS).
 320                  * These adjustments MUST be applied only at the beginning of the
 321                  * connection.
 322                  *
 323                  * AWL was adjusted in dccp_v4_connect -acme
 324                  */
 325                 dccp_set_seqno(&dp->dccps_swl,
 326                                max48(dp->dccps_swl, dp->dccps_isr));
 327
 328                 if (ccid_hc_rx_init(dp->dccps_hc_rx_ccid, sk) != 0 ||
 329                     ccid_hc_tx_init(dp->dccps_hc_tx_ccid, sk) != 0) {
 330                         ccid_hc_rx_exit(dp->dccps_hc_rx_ccid, sk);
 331                         ccid_hc_tx_exit(dp->dccps_hc_tx_ccid, sk);
 332                         /* FIXME: send appropriate RESET code */
 333                         goto out_invalid_packet;
 334                 }
 335
 336                 dccp_sync_mss(sk, dp->dccps_pmtu_cookie);
 337
 338                 /*
 339                  *    Step 10: Process REQUEST state (second part)
 340                  *       If S.state == REQUEST,
 341                  *        / * If we get here, P is a valid Response from the
 342                  *            server (see Step 4), and we should move to
 343                  *            PARTOPEN state. PARTOPEN means send an Ack,
 344                  *            don't send Data packets, retransmit Acks
 345                  *            periodically, and always include any Init Cookie
 346                  *            from the Response * /
 347                  *        S.state := PARTOPEN
 348                  *        Set PARTOPEN timer
 349                  *        Continue with S.state == PARTOPEN
 350                  *        / * Step 12 will send the Ack completing the
 351                  *            three-way handshake * /
 352                  */
 353                 dccp_set_state(sk, DCCP_PARTOPEN);
 354
 355                 /* Make sure socket is routed, for correct metrics. */
 356                 inet_sk_rebuild_header(sk);
 357
 358                 if (!sock_flag(sk, SOCK_DEAD)) {
 359                         sk->sk_state_change(sk);
 360                         sk_wake_async(sk, 0, POLL_OUT);
 361                 }
 362
 363                 if (sk->sk_write_pending || icsk->icsk_ack.pingpong ||
 364                     icsk->icsk_accept_queue.rskq_defer_accept) {
 365                         /* Save one ACK. Data will be ready after
 366                          * several ticks, if write_pending is set.
 367                          *
 368                          * It may be deleted, but with this feature tcpdumps
 369                          * look so _wonderfully_ clever, that I was not able
 370                          * to stand against the temptation 8)     --ANK
 371                          */
 372                         /*
 373                          * OK, in DCCP we can as well do a similar trick, its
 374                          * even in the draft, but there is no need for us to
 375                          * schedule an ack here, as dccp_sendmsg does this for
 376                          * us, also stated in the draft. -acme
 377                          */
 378                         __kfree_skb(skb);
 379                         return 0;
 380                 }
 381                 dccp_send_ack(sk);
 382                 return -1;
 383         }
 384
 385 out_invalid_packet:
 386         return 1; /* dccp_v4_do_rcv will send a reset, but...
 387                      FIXME: the reset code should be
 388                             DCCP_RESET_CODE_PACKET_ERROR */
 389 }
 390
 391 static int dccp_rcv_respond_partopen_state_process(struct sock *sk,
 392                                                    struct sk_buff *skb,
 393                                                    const struct dccp_hdr *dh,
 394                                                    const unsigned len)
 395 {
 396         int queued = 0;
 397
 398         switch (dh->dccph_type) {
 399         case DCCP_PKT_RESET:
 400                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
 401                 break;
 402         case DCCP_PKT_DATAACK:
 403         case DCCP_PKT_ACK:
 404                 /*
 405                  * FIXME: we should be reseting the PARTOPEN (DELACK) timer
 406                  * here but only if we haven't used the DELACK timer for
 407                  * something else, like sending a delayed ack for a TIMESTAMP
 408                  * echo, etc, for now were not clearing it, sending an extra
 409                  * ACK when there is nothing else to do in DELACK is not a big
 410                  * deal after all.
 411                  */
 412
 413                 /* Stop the PARTOPEN timer */
 414                 if (sk->sk_state == DCCP_PARTOPEN)
 415                         inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
 416
 417                 dccp_sk(sk)->dccps_osr = DCCP_SKB_CB(skb)->dccpd_seq;
 418                 dccp_set_state(sk, DCCP_OPEN);
 419
 420                 if (dh->dccph_type == DCCP_PKT_DATAACK) {
 421                         dccp_rcv_established(sk, skb, dh, len);
 422                         queued = 1; /* packet was queued
 423                                        (by dccp_rcv_established) */
 424                 }
 425                 break;
 426         }
 427
 428         return queued;
 429 }
 430
 431 int dccp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
 432                            struct dccp_hdr *dh, unsigned len)
 433 {
 434         struct dccp_sock *dp = dccp_sk(sk);
 435         const int old_state = sk->sk_state;
 436         int queued = 0;
 437
 438         /*
 439          *  Step 3: Process LISTEN state
 440          *      (Continuing from dccp_v4_do_rcv and dccp_v6_do_rcv)
 441          *
 442          *     If S.state == LISTEN,
 443          *        If P.type == Request or P contains a valid Init Cookie
 444          *              option,
 445          *           * Must scan the packet's options to check for an Init
 446          *              Cookie.  Only the Init Cookie is processed here,
 447          *              however; other options are processed in Step 8.  This
 448          *              scan need only be performed if the endpoint uses Init
 449          *              Cookies *
 450          *           * Generate a new socket and switch to that socket *
 451          *           Set S := new socket for this port pair
 452          *           S.state = RESPOND
 453          *           Choose S.ISS (initial seqno) or set from Init Cookie
 454          *           Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookie
 455          *           Continue with S.state == RESPOND
 456          *           * A Response packet will be generated in Step 11 *
 457          *        Otherwise,
 458          *           Generate Reset(No Connection) unless P.type == Reset
 459          *           Drop packet and return
 460          *
 461          * NOTE: the check for the packet types is done in
 462          *       dccp_rcv_state_process
 463          */
 464         if (sk->sk_state == DCCP_LISTEN) {
 465                 if (dh->dccph_type == DCCP_PKT_REQUEST) {
 466                         if (dccp_v4_conn_request(sk, skb) < 0)
 467                                 return 1;
 468
 469                         /* FIXME: do congestion control initialization */
 470                         goto discard;
 471                 }
 472                 if (dh->dccph_type == DCCP_PKT_RESET)
 473                         goto discard;
 474
 475                 /* Caller (dccp_v4_do_rcv) will send Reset(No Connection)*/
 476                 return 1;
 477         }
 478
 479         if (sk->sk_state != DCCP_REQUESTING) {
 480                 if (dccp_check_seqno(sk, skb))
 481                         goto discard;
 482
 483                 /*
 484                  * Step 8: Process options and mark acknowledgeable
 485                  */
 486                 if (dccp_parse_options(sk, skb))
 487                         goto discard;
 488
 489                 if (DCCP_SKB_CB(skb)->dccpd_ack_seq !=
 490                     DCCP_PKT_WITHOUT_ACK_SEQ)
 491                         dccp_event_ack_recv(sk, skb);
 492
 493                 ccid_hc_rx_packet_recv(dp->dccps_hc_rx_ccid, sk, skb);
 494                 ccid_hc_tx_packet_recv(dp->dccps_hc_tx_ccid, sk, skb);
 495
 496                 /*
 497                  * FIXME: check ECN to see if we should use
 498                  * DCCP_ACKPKTS_STATE_ECN_MARKED
 499                  */
 500                 if (dp->dccps_options.dccpo_send_ack_vector) {
 501                         if (dccp_ackpkts_add(dp->dccps_hc_rx_ackpkts,
 502                                              DCCP_SKB_CB(skb)->dccpd_seq,
 503                                              DCCP_ACKPKTS_STATE_RECEIVED))
 504                                 goto discard;
 505                         /*
 506                          * FIXME: this activation is probably wrong, have to
 507                          * study more TCP delack machinery and how it fits into
 508                          * DCCP draft, but for now it kinda "works" 8)
 509                          */
 510                         if ((dp->dccps_hc_rx_ackpkts->dccpap_ack_seqno ==
 511                              DCCP_MAX_SEQNO + 1) &&
 512                             !inet_csk_ack_scheduled(sk)) {
 513                                 inet_csk_schedule_ack(sk);
 514                                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
 515                                                           TCP_DELACK_MIN,
 516                                                           DCCP_RTO_MAX);
 517                         }
 518                 }
 519         }
 520
 521         /*
 522          *  Step 9: Process Reset
 523          *      If P.type == Reset,
 524          *              Tear down connection
 525          *              S.state := TIMEWAIT
 526          *              Set TIMEWAIT timer
 527          *              Drop packet and return
 528         */
 529         if (dh->dccph_type == DCCP_PKT_RESET) {
 530                 /*
 531                  * Queue the equivalent of TCP fin so that dccp_recvmsg
 532                  * exits the loop
 533                  */
 534                 dccp_fin(sk, skb);
 535                 dccp_time_wait(sk, DCCP_TIME_WAIT, 0);
 536                 return 0;
 537                 /*
 538                  *   Step 7: Check for unexpected packet types
 539                  *      If (S.is_server and P.type == CloseReq)
 540                  *          or (S.is_server and P.type == Response)
 541                  *          or (S.is_client and P.type == Request)
 542                  *          or (S.state == RESPOND and P.type == Data),
 543                  *        Send Sync packet acknowledging P.seqno
 544                  *        Drop packet and return
 545                  */
 546         } else if ((dp->dccps_role != DCCP_ROLE_CLIENT &&
 547                     (dh->dccph_type == DCCP_PKT_RESPONSE ||
 548                      dh->dccph_type == DCCP_PKT_CLOSEREQ)) ||
 549                     (dp->dccps_role == DCCP_ROLE_CLIENT &&
 550                      dh->dccph_type == DCCP_PKT_REQUEST) ||
 551                     (sk->sk_state == DCCP_RESPOND &&
 552                      dh->dccph_type == DCCP_PKT_DATA)) {
 553                 dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq,
 554                                DCCP_PKT_SYNC);
 555                 goto discard;
 556         } else if (dh->dccph_type == DCCP_PKT_CLOSEREQ) {
 557                 dccp_rcv_closereq(sk, skb);
 558                 goto discard;
 559         } else if (dh->dccph_type == DCCP_PKT_CLOSE) {
 560                 dccp_rcv_close(sk, skb);
 561                 return 0;
 562         }
 563
 564         switch (sk->sk_state) {
 565         case DCCP_CLOSED:
 566                 return 1;
 567
 568         case DCCP_REQUESTING:
 569                 /* FIXME: do congestion control initialization */
 570
 571                 queued = dccp_rcv_request_sent_state_process(sk, skb, dh, len);
 572                 if (queued >= 0)
 573                         return queued;
 574
 575                 __kfree_skb(skb);
 576                 return 0;
 577
 578         case DCCP_RESPOND:
 579         case DCCP_PARTOPEN:
 580                 queued = dccp_rcv_respond_partopen_state_process(sk, skb,
 581                                                                  dh, len);
 582                 break;
 583         }
 584
 585         if (dh->dccph_type == DCCP_PKT_ACK ||
 586             dh->dccph_type == DCCP_PKT_DATAACK) {
 587                 switch (old_state) {
 588                 case DCCP_PARTOPEN:
 589                         sk->sk_state_change(sk);
 590                         sk_wake_async(sk, 0, POLL_OUT);
 591                         break;
 592                 }
 593         }
 594
 595         if (!queued) {
 596 discard:
 597                 __kfree_skb(skb);
 598         }
 599         return 0;
 600 }