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_can_append_data(struct sctp_packet *packet,
  65                                            struct sctp_chunk *chunk);
  66 static void sctp_packet_append_data(struct sctp_packet *packet,
  67                                            struct sctp_chunk *chunk);
  68 static sctp_xmit_t sctp_packet_will_fit(struct sctp_packet *packet,
  69                                         struct sctp_chunk *chunk,
  70                                         u16 chunk_len);
  71
  72 static void sctp_packet_reset(struct sctp_packet *packet)
  73 {
  74         packet->size = packet->overhead;
  75         packet->has_cookie_echo = 0;
  76         packet->has_sack = 0;
  77         packet->has_data = 0;
  78         packet->has_auth = 0;
  79         packet->ipfragok = 0;
  80         packet->auth = NULL;
  81 }
  82
  83 /* Config a packet.
  84  * This appears to be a followup set of initializations.
  85  */
  86 struct sctp_packet *sctp_packet_config(struct sctp_packet *packet,
  87                                        __u32 vtag, int ecn_capable)
  88 {
  89         struct sctp_chunk *chunk = NULL;
  90
  91         SCTP_DEBUG_PRINTK("%s: packet:%p vtag:0x%x\n", __func__,
  92                           packet, vtag);
  93
  94         packet->vtag = vtag;
  95
  96         if (ecn_capable && sctp_packet_empty(packet)) {
  97                 chunk = sctp_get_ecne_prepend(packet->transport->asoc);
  98
  99                 /* If there a is a prepend chunk stick it on the list before
 100                  * any other chunks get appended.
 101                  */
 102                 if (chunk)
 103                         sctp_packet_append_chunk(packet, chunk);
 104         }
 105
 106         return packet;
 107 }
 108
 109 /* Initialize the packet structure. */
 110 struct sctp_packet *sctp_packet_init(struct sctp_packet *packet,
 111                                      struct sctp_transport *transport,
 112                                      __u16 sport, __u16 dport)
 113 {
 114         struct sctp_association *asoc = transport->asoc;
 115         size_t overhead;
 116
 117         SCTP_DEBUG_PRINTK("%s: packet:%p transport:%p\n", __func__,
 118                           packet, transport);
 119
 120         packet->transport = transport;
 121         packet->source_port = sport;
 122         packet->destination_port = dport;
 123         INIT_LIST_HEAD(&packet->chunk_list);
 124         if (asoc) {
 125                 struct sctp_sock *sp = sctp_sk(asoc->base.sk);
 126                 overhead = sp->pf->af->net_header_len;
 127         } else {
 128                 overhead = sizeof(struct ipv6hdr);
 129         }
 130         overhead += sizeof(struct sctphdr);
 131         packet->overhead = overhead;
 132         sctp_packet_reset(packet);
 133         packet->vtag = 0;
 134         packet->malloced = 0;
 135         return packet;
 136 }
 137
 138 /* Free a packet.  */
 139 void sctp_packet_free(struct sctp_packet *packet)
 140 {
 141         struct sctp_chunk *chunk, *tmp;
 142
 143         SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);
 144
 145         list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
 146                 list_del_init(&chunk->list);
 147                 sctp_chunk_free(chunk);
 148         }
 149
 150         if (packet->malloced)
 151                 kfree(packet);
 152 }
 153
 154 /* This routine tries to append the chunk to the offered packet. If adding
 155  * the chunk causes the packet to exceed the path MTU and COOKIE_ECHO chunk
 156  * is not present in the packet, it transmits the input packet.
 157  * Data can be bundled with a packet containing a COOKIE_ECHO chunk as long
 158  * as it can fit in the packet, but any more data that does not fit in this
 159  * packet can be sent only after receiving the COOKIE_ACK.
 160  */
 161 sctp_xmit_t sctp_packet_transmit_chunk(struct sctp_packet *packet,
 162                                        struct sctp_chunk *chunk,
 163                                        int one_packet)
 164 {
 165         sctp_xmit_t retval;
 166         int error = 0;
 167
 168         SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__,
 169                           packet, chunk);
 170
 171         switch ((retval = (sctp_packet_append_chunk(packet, chunk)))) {
 172         case SCTP_XMIT_PMTU_FULL:
 173                 if (!packet->has_cookie_echo) {
 174                         error = sctp_packet_transmit(packet);
 175                         if (error < 0)
 176                                 chunk->skb->sk->sk_err = -error;
 177
 178                         /* If we have an empty packet, then we can NOT ever
 179                          * return PMTU_FULL.
 180                          */
 181                         if (!one_packet)
 182                                 retval = sctp_packet_append_chunk(packet,
 183                                                                   chunk);
 184                 }
 185                 break;
 186
 187         case SCTP_XMIT_RWND_FULL:
 188         case SCTP_XMIT_OK:
 189         case SCTP_XMIT_NAGLE_DELAY:
 190                 break;
 191         }
 192
 193         return retval;
 194 }
 195
 196 /* Try to bundle an auth chunk into the packet. */
 197 static sctp_xmit_t sctp_packet_bundle_auth(struct sctp_packet *pkt,
 198                                            struct sctp_chunk *chunk)
 199 {
 200         struct sctp_association *asoc = pkt->transport->asoc;
 201         struct sctp_chunk *auth;
 202         sctp_xmit_t retval = SCTP_XMIT_OK;
 203
 204         /* if we don't have an association, we can't do authentication */
 205         if (!asoc)
 206                 return retval;
 207
 208         /* See if this is an auth chunk we are bundling or if
 209          * auth is already bundled.
 210          */
 211         if (chunk->chunk_hdr->type == SCTP_CID_AUTH || pkt->has_auth)
 212                 return retval;
 213
 214         /* if the peer did not request this chunk to be authenticated,
 215          * don't do it
 216          */
 217         if (!chunk->auth)
 218                 return retval;
 219
 220         auth = sctp_make_auth(asoc);
 221         if (!auth)
 222                 return retval;
 223
 224         retval = sctp_packet_append_chunk(pkt, auth);
 225
 226         return retval;
 227 }
 228
 229 /* Try to bundle a SACK with the packet. */
 230 static sctp_xmit_t sctp_packet_bundle_sack(struct sctp_packet *pkt,
 231                                            struct sctp_chunk *chunk)
 232 {
 233         sctp_xmit_t retval = SCTP_XMIT_OK;
 234
 235         /* If sending DATA and haven't aleady bundled a SACK, try to
 236          * bundle one in to the packet.
 237          */
 238         if (sctp_chunk_is_data(chunk) && !pkt->has_sack &&
 239             !pkt->has_cookie_echo) {
 240                 struct sctp_association *asoc;
 241                 struct timer_list *timer;
 242                 asoc = pkt->transport->asoc;
 243                 timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];
 244
 245                 /* If the SACK timer is running, we have a pending SACK */
 246                 if (timer_pending(timer)) {
 247                         struct sctp_chunk *sack;
 248                         asoc->a_rwnd = asoc->rwnd;
 249                         sack = sctp_make_sack(asoc);
 250                         if (sack) {
 251                                 retval = sctp_packet_append_chunk(pkt, sack);
 252                                 asoc->peer.sack_needed = 0;
 253                                 if (del_timer(timer))
 254                                         sctp_association_put(asoc);
 255                         }
 256                 }
 257         }
 258         return retval;
 259 }
 260
 261 /* Append a chunk to the offered packet reporting back any inability to do
 262  * so.
 263  */
 264 sctp_xmit_t sctp_packet_append_chunk(struct sctp_packet *packet,
 265                                      struct sctp_chunk *chunk)
 266 {
 267         sctp_xmit_t retval = SCTP_XMIT_OK;
 268         __u16 chunk_len = WORD_ROUND(ntohs(chunk->chunk_hdr->length));
 269
 270         SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__, packet,
 271                           chunk);
 272
 273         /* Data chunks are special.  Before seeing what else we can
 274          * bundle into this packet, check to see if we are allowed to
 275          * send this DATA.
 276          */
 277         if (sctp_chunk_is_data(chunk)) {
 278                 retval = sctp_packet_can_append_data(packet, chunk);
 279                 if (retval != SCTP_XMIT_OK)
 280                         goto finish;
 281         }
 282
 283         /* Try to bundle AUTH chunk */
 284         retval = sctp_packet_bundle_auth(packet, chunk);
 285         if (retval != SCTP_XMIT_OK)
 286                 goto finish;
 287
 288         /* Try to bundle SACK chunk */
 289         retval = sctp_packet_bundle_sack(packet, chunk);
 290         if (retval != SCTP_XMIT_OK)
 291                 goto finish;
 292
 293         /* Check to see if this chunk will fit into the packet */
 294         retval = sctp_packet_will_fit(packet, chunk, chunk_len);
 295         if (retval != SCTP_XMIT_OK)
 296                 goto finish;
 297
 298         /* We believe that this chunk is OK to add to the packet */
 299         switch (chunk->chunk_hdr->type) {
 300             case SCTP_CID_DATA:
 301                 /* Account for the data being in the packet */
 302                 sctp_packet_append_data(packet, chunk);
 303                 /* Disallow SACK bundling after DATA. */
 304                 packet->has_sack = 1;
 305                 /* Disallow AUTH bundling after DATA */
 306                 packet->has_auth = 1;
 307                 /* Let it be knows that packet has DATA in it */
 308                 packet->has_data = 1;
 309                 /* timestamp the chunk for rtx purposes */
 310                 chunk->sent_at = jiffies;
 311                 break;
 312             case SCTP_CID_COOKIE_ECHO:
 313                 packet->has_cookie_echo = 1;
 314                 break;
 315
 316             case SCTP_CID_SACK:
 317                 packet->has_sack = 1;
 318                 break;
 319
 320             case SCTP_CID_AUTH:
 321                 packet->has_auth = 1;
 322                 packet->auth = chunk;
 323                 break;
 324         }
 325
 326         /* It is OK to send this chunk.  */
 327         list_add_tail(&chunk->list, &packet->chunk_list);
 328         packet->size += chunk_len;
 329         chunk->transport = packet->transport;
 330 finish:
 331         return retval;
 332 }
 333
 334 /* All packets are sent to the network through this function from
 335  * sctp_outq_tail().
 336  *
 337  * The return value is a normal kernel error return value.
 338  */
 339 int sctp_packet_transmit(struct sctp_packet *packet)
 340 {
 341         struct sctp_transport *tp = packet->transport;
 342         struct sctp_association *asoc = tp->asoc;
 343         struct sctphdr *sh;
 344         struct sk_buff *nskb;
 345         struct sctp_chunk *chunk, *tmp;
 346         struct sock *sk;
 347         int err = 0;
 348         int padding;            /* How much padding do we need?  */
 349         __u8 has_data = 0;
 350         struct dst_entry *dst = tp->dst;
 351         unsigned char *auth = NULL;     /* pointer to auth in skb data */
 352         __u32 cksum_buf_len = sizeof(struct sctphdr);
 353
 354         SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);
 355
 356         /* Do NOT generate a chunkless packet. */
 357         if (list_empty(&packet->chunk_list))
 358                 return err;
 359
 360         /* Set up convenience variables... */
 361         chunk = list_entry(packet->chunk_list.next, struct sctp_chunk, list);
 362         sk = chunk->skb->sk;
 363
 364         /* Allocate the new skb.  */
 365         nskb = alloc_skb(packet->size + LL_MAX_HEADER, GFP_ATOMIC);
 366         if (!nskb)
 367                 goto nomem;
 368
 369         /* Make sure the outbound skb has enough header room reserved. */
 370         skb_reserve(nskb, packet->overhead + LL_MAX_HEADER);
 371
 372         /* Set the owning socket so that we know where to get the
 373          * destination IP address.
 374          */
 375         skb_set_owner_w(nskb, sk);
 376
 377         /* The 'obsolete' field of dst is set to 2 when a dst is freed. */
 378         if (!dst || (dst->obsolete > 1)) {
 379                 dst_release(dst);
 380                 sctp_transport_route(tp, NULL, sctp_sk(sk));
 381                 if (asoc && (asoc->param_flags & SPP_PMTUD_ENABLE)) {
 382                         sctp_assoc_sync_pmtu(asoc);
 383                 }
 384         }
 385         dst = dst_clone(tp->dst);
 386         skb_dst_set(nskb, dst);
 387         if (!dst)
 388                 goto no_route;
 389
 390         /* Build the SCTP header.  */
 391         sh = (struct sctphdr *)skb_push(nskb, sizeof(struct sctphdr));
 392         skb_reset_transport_header(nskb);
 393         sh->source = htons(packet->source_port);
 394         sh->dest   = htons(packet->destination_port);
 395
 396         /* From 6.8 Adler-32 Checksum Calculation:
 397          * After the packet is constructed (containing the SCTP common
 398          * header and one or more control or DATA chunks), the
 399          * transmitter shall:
 400          *
 401          * 1) Fill in the proper Verification Tag in the SCTP common
 402          *    header and initialize the checksum field to 0's.
 403          */
 404         sh->vtag     = htonl(packet->vtag);
 405         sh->checksum = 0;
 406
 407         /**
 408          * 6.10 Bundling
 409          *
 410          *    An endpoint bundles chunks by simply including multiple
 411          *    chunks in one outbound SCTP packet.  ...
 412          */
 413
 414         /**
 415          * 3.2  Chunk Field Descriptions
 416          *
 417          * The total length of a chunk (including Type, Length and
 418          * Value fields) MUST be a multiple of 4 bytes.  If the length
 419          * of the chunk is not a multiple of 4 bytes, the sender MUST
 420          * pad the chunk with all zero bytes and this padding is not
 421          * included in the chunk length field.  The sender should
 422          * never pad with more than 3 bytes.
 423          *
 424          * [This whole comment explains WORD_ROUND() below.]
 425          */
 426         SCTP_DEBUG_PRINTK("***sctp_transmit_packet***\n");
 427         list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
 428                 list_del_init(&chunk->list);
 429                 if (sctp_chunk_is_data(chunk)) {
 430
 431                         if (!chunk->has_tsn) {
 432                                 sctp_chunk_assign_ssn(chunk);
 433                                 sctp_chunk_assign_tsn(chunk);
 434
 435                         /* 6.3.1 C4) When data is in flight and when allowed
 436                          * by rule C5, a new RTT measurement MUST be made each
 437                          * round trip.  Furthermore, new RTT measurements
 438                          * SHOULD be made no more than once per round-trip
 439                          * for a given destination transport address.
 440                          */
 441
 442                                 if (!tp->rto_pending) {
 443                                         chunk->rtt_in_progress = 1;
 444                                         tp->rto_pending = 1;
 445                                 }
 446                         } else
 447                                 chunk->resent = 1;
 448
 449                         has_data = 1;
 450                 }
 451
 452                 padding = WORD_ROUND(chunk->skb->len) - chunk->skb->len;
 453                 if (padding)
 454                         memset(skb_put(chunk->skb, padding), 0, padding);
 455
 456                 /* if this is the auth chunk that we are adding,
 457                  * store pointer where it will be added and put
 458                  * the auth into the packet.
 459                  */
 460                 if (chunk == packet->auth)
 461                         auth = skb_tail_pointer(nskb);
 462
 463                 cksum_buf_len += chunk->skb->len;
 464                 memcpy(skb_put(nskb, chunk->skb->len),
 465                                chunk->skb->data, chunk->skb->len);
 466
 467                 SCTP_DEBUG_PRINTK("%s %p[%s] %s 0x%x, %s %d, %s %d, %s %d\n",
 468                                   "*** Chunk", chunk,
 469                                   sctp_cname(SCTP_ST_CHUNK(
 470                                           chunk->chunk_hdr->type)),
 471                                   chunk->has_tsn ? "TSN" : "No TSN",
 472                                   chunk->has_tsn ?
 473                                   ntohl(chunk->subh.data_hdr->tsn) : 0,
 474                                   "length", ntohs(chunk->chunk_hdr->length),
 475                                   "chunk->skb->len", chunk->skb->len,
 476                                   "rtt_in_progress", chunk->rtt_in_progress);
 477
 478                 /*
 479                  * If this is a control chunk, this is our last
 480                  * reference. Free data chunks after they've been
 481                  * acknowledged or have failed.
 482                  */
 483                 if (!sctp_chunk_is_data(chunk))
 484                         sctp_chunk_free(chunk);
 485         }
 486
 487         /* SCTP-AUTH, Section 6.2
 488          *    The sender MUST calculate the MAC as described in RFC2104 [2]
 489          *    using the hash function H as described by the MAC Identifier and
 490          *    the shared association key K based on the endpoint pair shared key
 491          *    described by the shared key identifier.  The 'data' used for the
 492          *    computation of the AUTH-chunk is given by the AUTH chunk with its
 493          *    HMAC field set to zero (as shown in Figure 6) followed by all
 494          *    chunks that are placed after the AUTH chunk in the SCTP packet.
 495          */
 496         if (auth)
 497                 sctp_auth_calculate_hmac(asoc, nskb,
 498                                         (struct sctp_auth_chunk *)auth,
 499                                         GFP_ATOMIC);
 500
 501         /* 2) Calculate the Adler-32 checksum of the whole packet,
 502          *    including the SCTP common header and all the
 503          *    chunks.
 504          *
 505          * Note: Adler-32 is no longer applicable, as has been replaced
 506          * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
 507          */
 508         if (!sctp_checksum_disable &&
 509             !(dst->dev->features & (NETIF_F_NO_CSUM | NETIF_F_SCTP_CSUM))) {
 510                 __u32 crc32 = sctp_start_cksum((__u8 *)sh, cksum_buf_len);
 511
 512                 /* 3) Put the resultant value into the checksum field in the
 513                  *    common header, and leave the rest of the bits unchanged.
 514                  */
 515                 sh->checksum = sctp_end_cksum(crc32);
 516         } else {
 517                 if (dst->dev->features & NETIF_F_SCTP_CSUM) {
 518                         /* no need to seed psuedo checksum for SCTP */
 519                         nskb->ip_summed = CHECKSUM_PARTIAL;
 520                         nskb->csum_start = (skb_transport_header(nskb) -
 521                                             nskb->head);
 522                         nskb->csum_offset = offsetof(struct sctphdr, checksum);
 523                 } else {
 524                         nskb->ip_summed = CHECKSUM_UNNECESSARY;
 525                 }
 526         }
 527
 528         /* IP layer ECN support
 529          * From RFC 2481
 530          *  "The ECN-Capable Transport (ECT) bit would be set by the
 531          *   data sender to indicate that the end-points of the
 532          *   transport protocol are ECN-capable."
 533          *
 534          * Now setting the ECT bit all the time, as it should not cause
 535          * any problems protocol-wise even if our peer ignores it.
 536          *
 537          * Note: The works for IPv6 layer checks this bit too later
 538          * in transmission.  See IP6_ECN_flow_xmit().
 539          */
 540         (*tp->af_specific->ecn_capable)(nskb->sk);
 541
 542         /* Set up the IP options.  */
 543         /* BUG: not implemented
 544          * For v4 this all lives somewhere in sk->sk_opt...
 545          */
 546
 547         /* Dump that on IP!  */
 548         if (asoc && asoc->peer.last_sent_to != tp) {
 549                 /* Considering the multiple CPU scenario, this is a
 550                  * "correcter" place for last_sent_to.  --xguo
 551                  */
 552                 asoc->peer.last_sent_to = tp;
 553         }
 554
 555         if (has_data) {
 556                 struct timer_list *timer;
 557                 unsigned long timeout;
 558
 559                 tp->last_time_used = jiffies;
 560
 561                 /* Restart the AUTOCLOSE timer when sending data. */
 562                 if (sctp_state(asoc, ESTABLISHED) && asoc->autoclose) {
 563                         timer = &asoc->timers[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
 564                         timeout = asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
 565
 566                         if (!mod_timer(timer, jiffies + timeout))
 567                                 sctp_association_hold(asoc);
 568                 }
 569         }
 570
 571         SCTP_DEBUG_PRINTK("***sctp_transmit_packet*** skb len %d\n",
 572                           nskb->len);
 573
 574         nskb->local_df = packet->ipfragok;
 575         (*tp->af_specific->sctp_xmit)(nskb, tp);
 576
 577 out:
 578         sctp_packet_reset(packet);
 579         return err;
 580 no_route:
 581         kfree_skb(nskb);
 582         IP_INC_STATS_BH(&init_net, IPSTATS_MIB_OUTNOROUTES);
 583
 584         /* FIXME: Returning the 'err' will effect all the associations
 585          * associated with a socket, although only one of the paths of the
 586          * association is unreachable.
 587          * The real failure of a transport or association can be passed on
 588          * to the user via notifications. So setting this error may not be
 589          * required.
 590          */
 591          /* err = -EHOSTUNREACH; */
 592 err:
 593         /* Control chunks are unreliable so just drop them.  DATA chunks
 594          * will get resent or dropped later.
 595          */
 596
 597         list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
 598                 list_del_init(&chunk->list);
 599                 if (!sctp_chunk_is_data(chunk))
 600                         sctp_chunk_free(chunk);
 601         }
 602         goto out;
 603 nomem:
 604         err = -ENOMEM;
 605         goto err;
 606 }
 607
 608 /********************************************************************
 609  * 2nd Level Abstractions
 610  ********************************************************************/
 611
 612 /* This private function check to see if a chunk can be added */
 613 static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
 614                                            struct sctp_chunk *chunk)
 615 {
 616         sctp_xmit_t retval = SCTP_XMIT_OK;
 617         size_t datasize, rwnd, inflight, flight_size;
 618         struct sctp_transport *transport = packet->transport;
 619         __u32 max_burst_bytes;
 620         struct sctp_association *asoc = transport->asoc;
 621         struct sctp_outq *q = &asoc->outqueue;
 622
 623         /* RFC 2960 6.1  Transmission of DATA Chunks
 624          *
 625          * A) At any given time, the data sender MUST NOT transmit new data to
 626          * any destination transport address if its peer's rwnd indicates
 627          * that the peer has no buffer space (i.e. rwnd is 0, see Section
 628          * 6.2.1).  However, regardless of the value of rwnd (including if it
 629          * is 0), the data sender can always have one DATA chunk in flight to
 630          * the receiver if allowed by cwnd (see rule B below).  This rule
 631          * allows the sender to probe for a change in rwnd that the sender
 632          * missed due to the SACK having been lost in transit from the data
 633          * receiver to the data sender.
 634          */
 635
 636         rwnd = asoc->peer.rwnd;
 637         inflight = q->outstanding_bytes;
 638         flight_size = transport->flight_size;
 639
 640         datasize = sctp_data_size(chunk);
 641
 642         if (datasize > rwnd) {
 643                 if (inflight > 0) {
 644                         /* We have (at least) one data chunk in flight,
 645                          * so we can't fall back to rule 6.1 B).
 646                          */
 647                         retval = SCTP_XMIT_RWND_FULL;
 648                         goto finish;
 649                 }
 650         }
 651
 652         /* sctpimpguide-05 2.14.2
 653          * D) When the time comes for the sender to
 654          * transmit new DATA chunks, the protocol parameter Max.Burst MUST
 655          * first be applied to limit how many new DATA chunks may be sent.
 656          * The limit is applied by adjusting cwnd as follows:
 657          *      if ((flightsize + Max.Burst * MTU) < cwnd)
 658          *              cwnd = flightsize + Max.Burst * MTU
 659          */
 660         max_burst_bytes = asoc->max_burst * asoc->pathmtu;
 661         if ((flight_size + max_burst_bytes) < transport->cwnd) {
 662                 transport->cwnd = flight_size + max_burst_bytes;
 663                 SCTP_DEBUG_PRINTK("%s: cwnd limited by max_burst: "
 664                                   "transport: %p, cwnd: %d, "
 665                                   "ssthresh: %d, flight_size: %d, "
 666                                   "pba: %d\n",
 667                                   __func__, transport,
 668                                   transport->cwnd,
 669                                   transport->ssthresh,
 670                                   transport->flight_size,
 671                                   transport->partial_bytes_acked);
 672         }
 673
 674         /* RFC 2960 6.1  Transmission of DATA Chunks
 675          *
 676          * B) At any given time, the sender MUST NOT transmit new data
 677          * to a given transport address if it has cwnd or more bytes
 678          * of data outstanding to that transport address.
 679          */
 680         /* RFC 7.2.4 & the Implementers Guide 2.8.
 681          *
 682          * 3) ...
 683          *    When a Fast Retransmit is being performed the sender SHOULD
 684          *    ignore the value of cwnd and SHOULD NOT delay retransmission.
 685          */
 686         if (chunk->fast_retransmit != SCTP_NEED_FRTX)
 687                 if (flight_size >= transport->cwnd) {
 688                         retval = SCTP_XMIT_RWND_FULL;
 689                         goto finish;
 690                 }
 691
 692         /* Nagle's algorithm to solve small-packet problem:
 693          * Inhibit the sending of new chunks when new outgoing data arrives
 694          * if any previously transmitted data on the connection remains
 695          * unacknowledged.
 696          */
 697         if (!sctp_sk(asoc->base.sk)->nodelay && sctp_packet_empty(packet) &&
 698             inflight && sctp_state(asoc, ESTABLISHED)) {
 699                 unsigned max = transport->pathmtu - packet->overhead;
 700                 unsigned len = chunk->skb->len + q->out_qlen;
 701
 702                 /* Check whether this chunk and all the rest of pending
 703                  * data will fit or delay in hopes of bundling a full
 704                  * sized packet.
 705                  * Don't delay large message writes that may have been
 706                  * fragmeneted into small peices.
 707                  */
 708                 if ((len < max) && (chunk->msg->msg_size < max)) {
 709                         retval = SCTP_XMIT_NAGLE_DELAY;
 710                         goto finish;
 711                 }
 712         }
 713
 714 finish:
 715         return retval;
 716 }
 717
 718 /* This private function does management things when adding DATA chunk */
 719 static void sctp_packet_append_data(struct sctp_packet *packet,
 720                                 struct sctp_chunk *chunk)
 721 {
 722         struct sctp_transport *transport = packet->transport;
 723         size_t datasize = sctp_data_size(chunk);
 724         struct sctp_association *asoc = transport->asoc;
 725         u32 rwnd = asoc->peer.rwnd;
 726
 727         /* Keep track of how many bytes are in flight over this transport. */
 728         transport->flight_size += datasize;
 729
 730         /* Keep track of how many bytes are in flight to the receiver. */
 731         asoc->outqueue.outstanding_bytes += datasize;
 732
 733         /* Update our view of the receiver's rwnd. Include sk_buff overhead
 734          * while updating peer.rwnd so that it reduces the chances of a
 735          * receiver running out of receive buffer space even when receive
 736          * window is still open. This can happen when a sender is sending
 737          * sending small messages.
 738          */
 739         datasize += sizeof(struct sk_buff);
 740         if (datasize < rwnd)
 741                 rwnd -= datasize;
 742         else
 743                 rwnd = 0;
 744
 745         asoc->peer.rwnd = rwnd;
 746         /* Has been accepted for transmission. */
 747         if (!asoc->peer.prsctp_capable)
 748                 chunk->msg->can_abandon = 0;
 749 }
 750
 751 static sctp_xmit_t sctp_packet_will_fit(struct sctp_packet *packet,
 752                                         struct sctp_chunk *chunk,
 753                                         u16 chunk_len)
 754 {
 755         size_t psize;
 756         size_t pmtu;
 757         int too_big;
 758         sctp_xmit_t retval = SCTP_XMIT_OK;
 759
 760         psize = packet->size;
 761         pmtu  = ((packet->transport->asoc) ?
 762                 (packet->transport->asoc->pathmtu) :
 763                 (packet->transport->pathmtu));
 764
 765         too_big = (psize + chunk_len > pmtu);
 766
 767         /* Decide if we need to fragment or resubmit later. */
 768         if (too_big) {
 769                 /* It's OK to fragmet at IP level if any one of the following
 770                  * is true:
 771                  *      1. The packet is empty (meaning this chunk is greater
 772                  *         the MTU)
 773                  *      2. The chunk we are adding is a control chunk
 774                  *      3. The packet doesn't have any data in it yet and data
 775                  *      requires authentication.
 776                  */
 777                 if (sctp_packet_empty(packet) || !sctp_chunk_is_data(chunk) ||
 778                     (!packet->has_data && chunk->auth)) {
 779                         /* We no longer do re-fragmentation.
 780                          * Just fragment at the IP layer, if we
 781                          * actually hit this condition
 782                          */
 783                         packet->ipfragok = 1;
 784                 } else {
 785                         retval = SCTP_XMIT_PMTU_FULL;
 786                 }
 787         }
 788
 789         return retval;
 790 }