net/sctp/output.c

   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. */
  64 static 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  */
  70 struct 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. */
 100 struct 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.  */
 135 void 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  */
 157 sctp_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. */
 193 static 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. */
 226 static 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  */
 259 sctp_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
 313 append:
 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;
 353 finish:
 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  */
 362 int 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
 589 out:
 590         packet->size = packet->overhead;
 591         return err;
 592 no_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; */
 604 err:
 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;
 615 nomem:
 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.  */
 625 static 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
 746 finish:
 747         return retval;
 748 }