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