linux/net/sctp/output.c
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   1/* SCTP kernel implementation
   2 * (C) Copyright IBM Corp. 2001, 2004
   3 * Copyright (c) 1999-2000 Cisco, Inc.
   4 * Copyright (c) 1999-2001 Motorola, Inc.
   5 *
   6 * This file is part of the SCTP kernel implementation
   7 *
   8 * These functions handle output processing.
   9 *
  10 * This SCTP implementation is free software;
  11 * you can redistribute it and/or modify it under the terms of
  12 * the GNU General Public License as published by
  13 * the Free Software Foundation; either version 2, or (at your option)
  14 * any later version.
  15 *
  16 * This SCTP implementation is distributed in the hope that it
  17 * will be useful, but WITHOUT ANY WARRANTY; without even the implied
  18 *                 ************************
  19 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  20 * See the GNU General Public License for more details.
  21 *
  22 * You should have received a copy of the GNU General Public License
  23 * along with GNU CC; see the file COPYING.  If not, write to
  24 * the Free Software Foundation, 59 Temple Place - Suite 330,
  25 * Boston, MA 02111-1307, USA.
  26 *
  27 * Please send any bug reports or fixes you make to the
  28 * email address(es):
  29 *    lksctp developers <lksctp-developers@lists.sourceforge.net>
  30 *
  31 * Or submit a bug report through the following website:
  32 *    http://www.sf.net/projects/lksctp
  33 *
  34 * Written or modified by:
  35 *    La Monte H.P. Yarroll <piggy@acm.org>
  36 *    Karl Knutson          <karl@athena.chicago.il.us>
  37 *    Jon Grimm             <jgrimm@austin.ibm.com>
  38 *    Sridhar Samudrala     <sri@us.ibm.com>
  39 *
  40 * Any bugs reported given to us we will try to fix... any fixes shared will
  41 * be incorporated into the next SCTP release.
  42 */
  43
  44#include <linux/types.h>
  45#include <linux/kernel.h>
  46#include <linux/wait.h>
  47#include <linux/time.h>
  48#include <linux/ip.h>
  49#include <linux/ipv6.h>
  50#include <linux/init.h>
  51#include <net/inet_ecn.h>
  52#include <net/ip.h>
  53#include <net/icmp.h>
  54#include <net/net_namespace.h>
  55
  56#include <linux/socket.h> /* for sa_family_t */
  57#include <net/sock.h>
  58
  59#include <net/sctp/sctp.h>
  60#include <net/sctp/sm.h>
  61#include <net/sctp/checksum.h>
  62
  63/* Forward declarations for private helpers. */
  64static sctp_xmit_t sctp_packet_append_data(struct sctp_packet *packet,
  65                                           struct sctp_chunk *chunk);
  66
  67/* Config a packet.
  68 * This appears to be a followup set of initializations.
  69 */
  70struct sctp_packet *sctp_packet_config(struct sctp_packet *packet,
  71                                       __u32 vtag, int ecn_capable)
  72{
  73        struct sctp_chunk *chunk = NULL;
  74
  75        SCTP_DEBUG_PRINTK("%s: packet:%p vtag:0x%x\n", __func__,
  76                          packet, vtag);
  77
  78        packet->vtag = vtag;
  79        packet->has_cookie_echo = 0;
  80        packet->has_sack = 0;
  81        packet->has_auth = 0;
  82        packet->has_data = 0;
  83        packet->ipfragok = 0;
  84        packet->auth = NULL;
  85
  86        if (ecn_capable && sctp_packet_empty(packet)) {
  87                chunk = sctp_get_ecne_prepend(packet->transport->asoc);
  88
  89                /* If there a is a prepend chunk stick it on the list before
  90                 * any other chunks get appended.
  91                 */
  92                if (chunk)
  93                        sctp_packet_append_chunk(packet, chunk);
  94        }
  95
  96        return packet;
  97}
  98
  99/* Initialize the packet structure. */
 100struct sctp_packet *sctp_packet_init(struct sctp_packet *packet,
 101                                     struct sctp_transport *transport,
 102                                     __u16 sport, __u16 dport)
 103{
 104        struct sctp_association *asoc = transport->asoc;
 105        size_t overhead;
 106
 107        SCTP_DEBUG_PRINTK("%s: packet:%p transport:%p\n", __func__,
 108                          packet, transport);
 109
 110        packet->transport = transport;
 111        packet->source_port = sport;
 112        packet->destination_port = dport;
 113        INIT_LIST_HEAD(&packet->chunk_list);
 114        if (asoc) {
 115                struct sctp_sock *sp = sctp_sk(asoc->base.sk);
 116                overhead = sp->pf->af->net_header_len;
 117        } else {
 118                overhead = sizeof(struct ipv6hdr);
 119        }
 120        overhead += sizeof(struct sctphdr);
 121        packet->overhead = overhead;
 122        packet->size = overhead;
 123        packet->vtag = 0;
 124        packet->has_cookie_echo = 0;
 125        packet->has_sack = 0;
 126        packet->has_auth = 0;
 127        packet->has_data = 0;
 128        packet->ipfragok = 0;
 129        packet->malloced = 0;
 130        packet->auth = NULL;
 131        return packet;
 132}
 133
 134/* Free a packet.  */
 135void sctp_packet_free(struct sctp_packet *packet)
 136{
 137        struct sctp_chunk *chunk, *tmp;
 138
 139        SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);
 140
 141        list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
 142                list_del_init(&chunk->list);
 143                sctp_chunk_free(chunk);
 144        }
 145
 146        if (packet->malloced)
 147                kfree(packet);
 148}
 149
 150/* This routine tries to append the chunk to the offered packet. If adding
 151 * the chunk causes the packet to exceed the path MTU and COOKIE_ECHO chunk
 152 * is not present in the packet, it transmits the input packet.
 153 * Data can be bundled with a packet containing a COOKIE_ECHO chunk as long
 154 * as it can fit in the packet, but any more data that does not fit in this
 155 * packet can be sent only after receiving the COOKIE_ACK.
 156 */
 157sctp_xmit_t sctp_packet_transmit_chunk(struct sctp_packet *packet,
 158                                       struct sctp_chunk *chunk,
 159                                       int one_packet)
 160{
 161        sctp_xmit_t retval;
 162        int error = 0;
 163
 164        SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__,
 165                          packet, chunk);
 166
 167        switch ((retval = (sctp_packet_append_chunk(packet, chunk)))) {
 168        case SCTP_XMIT_PMTU_FULL:
 169                if (!packet->has_cookie_echo) {
 170                        error = sctp_packet_transmit(packet);
 171                        if (error < 0)
 172                                chunk->skb->sk->sk_err = -error;
 173
 174                        /* If we have an empty packet, then we can NOT ever
 175                         * return PMTU_FULL.
 176                         */
 177                        if (!one_packet)
 178                                retval = sctp_packet_append_chunk(packet,
 179                                                                  chunk);
 180                }
 181                break;
 182
 183        case SCTP_XMIT_RWND_FULL:
 184        case SCTP_XMIT_OK:
 185        case SCTP_XMIT_NAGLE_DELAY:
 186                break;
 187        }
 188
 189        return retval;
 190}
 191
 192/* Try to bundle an auth chunk into the packet. */
 193static sctp_xmit_t sctp_packet_bundle_auth(struct sctp_packet *pkt,
 194                                           struct sctp_chunk *chunk)
 195{
 196        struct sctp_association *asoc = pkt->transport->asoc;
 197        struct sctp_chunk *auth;
 198        sctp_xmit_t retval = SCTP_XMIT_OK;
 199
 200        /* if we don't have an association, we can't do authentication */
 201        if (!asoc)
 202                return retval;
 203
 204        /* See if this is an auth chunk we are bundling or if
 205         * auth is already bundled.
 206         */
 207        if (chunk->chunk_hdr->type == SCTP_CID_AUTH || pkt->auth)
 208                return retval;
 209
 210        /* if the peer did not request this chunk to be authenticated,
 211         * don't do it
 212         */
 213        if (!chunk->auth)
 214                return retval;
 215
 216        auth = sctp_make_auth(asoc);
 217        if (!auth)
 218                return retval;
 219
 220        retval = sctp_packet_append_chunk(pkt, auth);
 221
 222        return retval;
 223}
 224
 225/* Try to bundle a SACK with the packet. */
 226static sctp_xmit_t sctp_packet_bundle_sack(struct sctp_packet *pkt,
 227                                           struct sctp_chunk *chunk)
 228{
 229        sctp_xmit_t retval = SCTP_XMIT_OK;
 230
 231        /* If sending DATA and haven't aleady bundled a SACK, try to
 232         * bundle one in to the packet.
 233         */
 234        if (sctp_chunk_is_data(chunk) && !pkt->has_sack &&
 235            !pkt->has_cookie_echo) {
 236                struct sctp_association *asoc;
 237                asoc = pkt->transport->asoc;
 238
 239                if (asoc->a_rwnd > asoc->rwnd) {
 240                        struct sctp_chunk *sack;
 241                        asoc->a_rwnd = asoc->rwnd;
 242                        sack = sctp_make_sack(asoc);
 243                        if (sack) {
 244                                struct timer_list *timer;
 245                                retval = sctp_packet_append_chunk(pkt, sack);
 246                                asoc->peer.sack_needed = 0;
 247                                timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];
 248                                if (timer_pending(timer) && del_timer(timer))
 249                                        sctp_association_put(asoc);
 250                        }
 251                }
 252        }
 253        return retval;
 254}
 255
 256/* Append a chunk to the offered packet reporting back any inability to do
 257 * so.
 258 */
 259sctp_xmit_t sctp_packet_append_chunk(struct sctp_packet *packet,
 260                                     struct sctp_chunk *chunk)
 261{
 262        sctp_xmit_t retval = SCTP_XMIT_OK;
 263        __u16 chunk_len = WORD_ROUND(ntohs(chunk->chunk_hdr->length));
 264        size_t psize;
 265        size_t pmtu;
 266        int too_big;
 267
 268        SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__, packet,
 269                          chunk);
 270
 271        /* Try to bundle AUTH chunk */
 272        retval = sctp_packet_bundle_auth(packet, chunk);
 273        if (retval != SCTP_XMIT_OK)
 274                goto finish;
 275
 276        /* Try to bundle SACK chunk */
 277        retval = sctp_packet_bundle_sack(packet, chunk);
 278        if (retval != SCTP_XMIT_OK)
 279                goto finish;
 280
 281        psize = packet->size;
 282        pmtu  = ((packet->transport->asoc) ?
 283                 (packet->transport->asoc->pathmtu) :
 284                 (packet->transport->pathmtu));
 285
 286        too_big = (psize + chunk_len > pmtu);
 287
 288        /* Decide if we need to fragment or resubmit later. */
 289        if (too_big) {
 290                /* It's OK to fragmet at IP level if any one of the following
 291                 * is true:
 292                 *      1. The packet is empty (meaning this chunk is greater
 293                 *         the MTU)
 294                 *      2. The chunk we are adding is a control chunk
 295                 *      3. The packet doesn't have any data in it yet and data
 296                 *      requires authentication.
 297                 */
 298                if (sctp_packet_empty(packet) || !sctp_chunk_is_data(chunk) ||
 299                    (!packet->has_data && chunk->auth)) {
 300                        /* We no longer do re-fragmentation.
 301                         * Just fragment at the IP layer, if we
 302                         * actually hit this condition
 303                         */
 304                        packet->ipfragok = 1;
 305                        goto append;
 306
 307                } else {
 308                        retval = SCTP_XMIT_PMTU_FULL;
 309                        goto finish;
 310                }
 311        }
 312
 313append:
 314        /* We believe that this chunk is OK to add to the packet (as
 315         * long as we have the cwnd for it).
 316         */
 317
 318        /* DATA is a special case since we must examine both rwnd and cwnd
 319         * before we send DATA.
 320         */
 321        switch (chunk->chunk_hdr->type) {
 322            case SCTP_CID_DATA:
 323                retval = sctp_packet_append_data(packet, chunk);
 324                if (SCTP_XMIT_OK != retval)
 325                        goto finish;
 326                /* Disallow SACK bundling after DATA. */
 327                packet->has_sack = 1;
 328                /* Disallow AUTH bundling after DATA */
 329                packet->has_auth = 1;
 330                /* Let it be knows that packet has DATA in it */
 331                packet->has_data = 1;
 332                /* timestamp the chunk for rtx purposes */
 333                chunk->sent_at = jiffies;
 334                break;
 335            case SCTP_CID_COOKIE_ECHO:
 336                packet->has_cookie_echo = 1;
 337                break;
 338
 339            case SCTP_CID_SACK:
 340                packet->has_sack = 1;
 341                break;
 342
 343            case SCTP_CID_AUTH:
 344                packet->has_auth = 1;
 345                packet->auth = chunk;
 346                break;
 347        }
 348
 349        /* It is OK to send this chunk.  */
 350        list_add_tail(&chunk->list, &packet->chunk_list);
 351        packet->size += chunk_len;
 352        chunk->transport = packet->transport;
 353finish:
 354        return retval;
 355}
 356
 357/* All packets are sent to the network through this function from
 358 * sctp_outq_tail().
 359 *
 360 * The return value is a normal kernel error return value.
 361 */
 362int sctp_packet_transmit(struct sctp_packet *packet)
 363{
 364        struct sctp_transport *tp = packet->transport;
 365        struct sctp_association *asoc = tp->asoc;
 366        struct sctphdr *sh;
 367        struct sk_buff *nskb;
 368        struct sctp_chunk *chunk, *tmp;
 369        struct sock *sk;
 370        int err = 0;
 371        int padding;            /* How much padding do we need?  */
 372        __u8 has_data = 0;
 373        struct dst_entry *dst = tp->dst;
 374        unsigned char *auth = NULL;     /* pointer to auth in skb data */
 375        __u32 cksum_buf_len = sizeof(struct sctphdr);
 376
 377        SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);
 378
 379        /* Do NOT generate a chunkless packet. */
 380        if (list_empty(&packet->chunk_list))
 381                return err;
 382
 383        /* Set up convenience variables... */
 384        chunk = list_entry(packet->chunk_list.next, struct sctp_chunk, list);
 385        sk = chunk->skb->sk;
 386
 387        /* Allocate the new skb.  */
 388        nskb = alloc_skb(packet->size + LL_MAX_HEADER, GFP_ATOMIC);
 389        if (!nskb)
 390                goto nomem;
 391
 392        /* Make sure the outbound skb has enough header room reserved. */
 393        skb_reserve(nskb, packet->overhead + LL_MAX_HEADER);
 394
 395        /* Set the owning socket so that we know where to get the
 396         * destination IP address.
 397         */
 398        skb_set_owner_w(nskb, sk);
 399
 400        /* The 'obsolete' field of dst is set to 2 when a dst is freed. */
 401        if (!dst || (dst->obsolete > 1)) {
 402                dst_release(dst);
 403                sctp_transport_route(tp, NULL, sctp_sk(sk));
 404                if (asoc && (asoc->param_flags & SPP_PMTUD_ENABLE)) {
 405                        sctp_assoc_sync_pmtu(asoc);
 406                }
 407        }
 408        nskb->dst = dst_clone(tp->dst);
 409        if (!nskb->dst)
 410                goto no_route;
 411        dst = nskb->dst;
 412
 413        /* Build the SCTP header.  */
 414        sh = (struct sctphdr *)skb_push(nskb, sizeof(struct sctphdr));
 415        sh->source = htons(packet->source_port);
 416        sh->dest   = htons(packet->destination_port);
 417
 418        /* From 6.8 Adler-32 Checksum Calculation:
 419         * After the packet is constructed (containing the SCTP common
 420         * header and one or more control or DATA chunks), the
 421         * transmitter shall:
 422         *
 423         * 1) Fill in the proper Verification Tag in the SCTP common
 424         *    header and initialize the checksum field to 0's.
 425         */
 426        sh->vtag     = htonl(packet->vtag);
 427        sh->checksum = 0;
 428
 429        /**
 430         * 6.10 Bundling
 431         *
 432         *    An endpoint bundles chunks by simply including multiple
 433         *    chunks in one outbound SCTP packet.  ...
 434         */
 435
 436        /**
 437         * 3.2  Chunk Field Descriptions
 438         *
 439         * The total length of a chunk (including Type, Length and
 440         * Value fields) MUST be a multiple of 4 bytes.  If the length
 441         * of the chunk is not a multiple of 4 bytes, the sender MUST
 442         * pad the chunk with all zero bytes and this padding is not
 443         * included in the chunk length field.  The sender should
 444         * never pad with more than 3 bytes.
 445         *
 446         * [This whole comment explains WORD_ROUND() below.]
 447         */
 448        SCTP_DEBUG_PRINTK("***sctp_transmit_packet***\n");
 449        list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
 450                list_del_init(&chunk->list);
 451                if (sctp_chunk_is_data(chunk)) {
 452
 453                        if (!chunk->has_tsn) {
 454                                sctp_chunk_assign_ssn(chunk);
 455                                sctp_chunk_assign_tsn(chunk);
 456
 457                        /* 6.3.1 C4) When data is in flight and when allowed
 458                         * by rule C5, a new RTT measurement MUST be made each
 459                         * round trip.  Furthermore, new RTT measurements
 460                         * SHOULD be made no more than once per round-trip
 461                         * for a given destination transport address.
 462                         */
 463
 464                                if (!tp->rto_pending) {
 465                                        chunk->rtt_in_progress = 1;
 466                                        tp->rto_pending = 1;
 467                                }
 468                        } else
 469                                chunk->resent = 1;
 470
 471                        has_data = 1;
 472                }
 473
 474                padding = WORD_ROUND(chunk->skb->len) - chunk->skb->len;
 475                if (padding)
 476                        memset(skb_put(chunk->skb, padding), 0, padding);
 477
 478                /* if this is the auth chunk that we are adding,
 479                 * store pointer where it will be added and put
 480                 * the auth into the packet.
 481                 */
 482                if (chunk == packet->auth)
 483                        auth = skb_tail_pointer(nskb);
 484
 485                cksum_buf_len += chunk->skb->len;
 486                memcpy(skb_put(nskb, chunk->skb->len),
 487                               chunk->skb->data, chunk->skb->len);
 488
 489                SCTP_DEBUG_PRINTK("%s %p[%s] %s 0x%x, %s %d, %s %d, %s %d\n",
 490                                  "*** Chunk", chunk,
 491                                  sctp_cname(SCTP_ST_CHUNK(
 492                                          chunk->chunk_hdr->type)),
 493                                  chunk->has_tsn ? "TSN" : "No TSN",
 494                                  chunk->has_tsn ?
 495                                  ntohl(chunk->subh.data_hdr->tsn) : 0,
 496                                  "length", ntohs(chunk->chunk_hdr->length),
 497                                  "chunk->skb->len", chunk->skb->len,
 498                                  "rtt_in_progress", chunk->rtt_in_progress);
 499
 500                /*
 501                 * If this is a control chunk, this is our last
 502                 * reference. Free data chunks after they've been
 503                 * acknowledged or have failed.
 504                 */
 505                if (!sctp_chunk_is_data(chunk))
 506                        sctp_chunk_free(chunk);
 507        }
 508
 509        /* SCTP-AUTH, Section 6.2
 510         *    The sender MUST calculate the MAC as described in RFC2104 [2]
 511         *    using the hash function H as described by the MAC Identifier and
 512         *    the shared association key K based on the endpoint pair shared key
 513         *    described by the shared key identifier.  The 'data' used for the
 514         *    computation of the AUTH-chunk is given by the AUTH chunk with its
 515         *    HMAC field set to zero (as shown in Figure 6) followed by all
 516         *    chunks that are placed after the AUTH chunk in the SCTP packet.
 517         */
 518        if (auth)
 519                sctp_auth_calculate_hmac(asoc, nskb,
 520                                        (struct sctp_auth_chunk *)auth,
 521                                        GFP_ATOMIC);
 522
 523        /* 2) Calculate the Adler-32 checksum of the whole packet,
 524         *    including the SCTP common header and all the
 525         *    chunks.
 526         *
 527         * Note: Adler-32 is no longer applicable, as has been replaced
 528         * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
 529         */
 530        if (!sctp_checksum_disable && !(dst->dev->features & NETIF_F_NO_CSUM)) {
 531                __u32 crc32 = sctp_start_cksum((__u8 *)sh, cksum_buf_len);
 532
 533                /* 3) Put the resultant value into the checksum field in the
 534                 *    common header, and leave the rest of the bits unchanged.
 535                 */
 536                sh->checksum = sctp_end_cksum(crc32);
 537        } else
 538                nskb->ip_summed = CHECKSUM_UNNECESSARY;
 539
 540        /* IP layer ECN support
 541         * From RFC 2481
 542         *  "The ECN-Capable Transport (ECT) bit would be set by the
 543         *   data sender to indicate that the end-points of the
 544         *   transport protocol are ECN-capable."
 545         *
 546         * Now setting the ECT bit all the time, as it should not cause
 547         * any problems protocol-wise even if our peer ignores it.
 548         *
 549         * Note: The works for IPv6 layer checks this bit too later
 550         * in transmission.  See IP6_ECN_flow_xmit().
 551         */
 552        (*tp->af_specific->ecn_capable)(nskb->sk);
 553
 554        /* Set up the IP options.  */
 555        /* BUG: not implemented
 556         * For v4 this all lives somewhere in sk->sk_opt...
 557         */
 558
 559        /* Dump that on IP!  */
 560        if (asoc && asoc->peer.last_sent_to != tp) {
 561                /* Considering the multiple CPU scenario, this is a
 562                 * "correcter" place for last_sent_to.  --xguo
 563                 */
 564                asoc->peer.last_sent_to = tp;
 565        }
 566
 567        if (has_data) {
 568                struct timer_list *timer;
 569                unsigned long timeout;
 570
 571                tp->last_time_used = jiffies;
 572
 573                /* Restart the AUTOCLOSE timer when sending data. */
 574                if (sctp_state(asoc, ESTABLISHED) && asoc->autoclose) {
 575                        timer = &asoc->timers[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
 576                        timeout = asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
 577
 578                        if (!mod_timer(timer, jiffies + timeout))
 579                                sctp_association_hold(asoc);
 580                }
 581        }
 582
 583        SCTP_DEBUG_PRINTK("***sctp_transmit_packet*** skb len %d\n",
 584                          nskb->len);
 585
 586        nskb->local_df = packet->ipfragok;
 587        (*tp->af_specific->sctp_xmit)(nskb, tp);
 588
 589out:
 590        packet->size = packet->overhead;
 591        return err;
 592no_route:
 593        kfree_skb(nskb);
 594        IP_INC_STATS_BH(&init_net, IPSTATS_MIB_OUTNOROUTES);
 595
 596        /* FIXME: Returning the 'err' will effect all the associations
 597         * associated with a socket, although only one of the paths of the
 598         * association is unreachable.
 599         * The real failure of a transport or association can be passed on
 600         * to the user via notifications. So setting this error may not be
 601         * required.
 602         */
 603         /* err = -EHOSTUNREACH; */
 604err:
 605        /* Control chunks are unreliable so just drop them.  DATA chunks
 606         * will get resent or dropped later.
 607         */
 608
 609        list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
 610                list_del_init(&chunk->list);
 611                if (!sctp_chunk_is_data(chunk))
 612                        sctp_chunk_free(chunk);
 613        }
 614        goto out;
 615nomem:
 616        err = -ENOMEM;
 617        goto err;
 618}
 619
 620/********************************************************************
 621 * 2nd Level Abstractions
 622 ********************************************************************/
 623
 624/* This private function handles the specifics of appending DATA chunks.  */
 625static sctp_xmit_t sctp_packet_append_data(struct sctp_packet *packet,
 626                                           struct sctp_chunk *chunk)
 627{
 628        sctp_xmit_t retval = SCTP_XMIT_OK;
 629        size_t datasize, rwnd, inflight;
 630        struct sctp_transport *transport = packet->transport;
 631        __u32 max_burst_bytes;
 632        struct sctp_association *asoc = transport->asoc;
 633        struct sctp_sock *sp = sctp_sk(asoc->base.sk);
 634        struct sctp_outq *q = &asoc->outqueue;
 635
 636        /* RFC 2960 6.1  Transmission of DATA Chunks
 637         *
 638         * A) At any given time, the data sender MUST NOT transmit new data to
 639         * any destination transport address if its peer's rwnd indicates
 640         * that the peer has no buffer space (i.e. rwnd is 0, see Section
 641         * 6.2.1).  However, regardless of the value of rwnd (including if it
 642         * is 0), the data sender can always have one DATA chunk in flight to
 643         * the receiver if allowed by cwnd (see rule B below).  This rule
 644         * allows the sender to probe for a change in rwnd that the sender
 645         * missed due to the SACK having been lost in transit from the data
 646         * receiver to the data sender.
 647         */
 648
 649        rwnd = asoc->peer.rwnd;
 650        inflight = asoc->outqueue.outstanding_bytes;
 651
 652        datasize = sctp_data_size(chunk);
 653
 654        if (datasize > rwnd) {
 655                if (inflight > 0) {
 656                        /* We have (at least) one data chunk in flight,
 657                         * so we can't fall back to rule 6.1 B).
 658                         */
 659                        retval = SCTP_XMIT_RWND_FULL;
 660                        goto finish;
 661                }
 662        }
 663
 664        /* sctpimpguide-05 2.14.2
 665         * D) When the time comes for the sender to
 666         * transmit new DATA chunks, the protocol parameter Max.Burst MUST
 667         * first be applied to limit how many new DATA chunks may be sent.
 668         * The limit is applied by adjusting cwnd as follows:
 669         *      if ((flightsize + Max.Burst * MTU) < cwnd)
 670         *              cwnd = flightsize + Max.Burst * MTU
 671         */
 672        max_burst_bytes = asoc->max_burst * asoc->pathmtu;
 673        if ((transport->flight_size + max_burst_bytes) < transport->cwnd) {
 674                transport->cwnd = transport->flight_size + max_burst_bytes;
 675                SCTP_DEBUG_PRINTK("%s: cwnd limited by max_burst: "
 676                                  "transport: %p, cwnd: %d, "
 677                                  "ssthresh: %d, flight_size: %d, "
 678                                  "pba: %d\n",
 679                                  __func__, transport,
 680                                  transport->cwnd,
 681                                  transport->ssthresh,
 682                                  transport->flight_size,
 683                                  transport->partial_bytes_acked);
 684        }
 685
 686        /* RFC 2960 6.1  Transmission of DATA Chunks
 687         *
 688         * B) At any given time, the sender MUST NOT transmit new data
 689         * to a given transport address if it has cwnd or more bytes
 690         * of data outstanding to that transport address.
 691         */
 692        /* RFC 7.2.4 & the Implementers Guide 2.8.
 693         *
 694         * 3) ...
 695         *    When a Fast Retransmit is being performed the sender SHOULD
 696         *    ignore the value of cwnd and SHOULD NOT delay retransmission.
 697         */
 698        if (chunk->fast_retransmit != SCTP_NEED_FRTX)
 699                if (transport->flight_size >= transport->cwnd) {
 700                        retval = SCTP_XMIT_RWND_FULL;
 701                        goto finish;
 702                }
 703
 704        /* Nagle's algorithm to solve small-packet problem:
 705         * Inhibit the sending of new chunks when new outgoing data arrives
 706         * if any previously transmitted data on the connection remains
 707         * unacknowledged.
 708         */
 709        if (!sp->nodelay && sctp_packet_empty(packet) &&
 710            q->outstanding_bytes && sctp_state(asoc, ESTABLISHED)) {
 711                unsigned len = datasize + q->out_qlen;
 712
 713                /* Check whether this chunk and all the rest of pending
 714                 * data will fit or delay in hopes of bundling a full
 715                 * sized packet.
 716                 */
 717                if (len < asoc->frag_point) {
 718                        retval = SCTP_XMIT_NAGLE_DELAY;
 719                        goto finish;
 720                }
 721        }
 722
 723        /* Keep track of how many bytes are in flight over this transport. */
 724        transport->flight_size += datasize;
 725
 726        /* Keep track of how many bytes are in flight to the receiver. */
 727        asoc->outqueue.outstanding_bytes += datasize;
 728
 729        /* Update our view of the receiver's rwnd. Include sk_buff overhead
 730         * while updating peer.rwnd so that it reduces the chances of a
 731         * receiver running out of receive buffer space even when receive
 732         * window is still open. This can happen when a sender is sending
 733         * sending small messages.
 734         */
 735        datasize += sizeof(struct sk_buff);
 736        if (datasize < rwnd)
 737                rwnd -= datasize;
 738        else
 739                rwnd = 0;
 740
 741        asoc->peer.rwnd = rwnd;
 742        /* Has been accepted for transmission. */
 743        if (!asoc->peer.prsctp_capable)
 744                chunk->msg->can_abandon = 0;
 745
 746finish:
 747        return retval;
 748}
 749