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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  45
  46 #include <linux/types.h>
  47 #include <linux/kernel.h>
  48 #include <linux/wait.h>
  49 #include <linux/time.h>
  50 #include <linux/ip.h>
  51 #include <linux/ipv6.h>
  52 #include <linux/init.h>
  53 #include <linux/slab.h>
  54 #include <net/inet_ecn.h>
  55 #include <net/ip.h>
  56 #include <net/icmp.h>
  57 #include <net/net_namespace.h>
  58
  59 #include <linux/socket.h> /* for sa_family_t */
  60 #include <net/sock.h>
  61
  62 #include <net/sctp/sctp.h>
  63 #include <net/sctp/sm.h>
  64 #include <net/sctp/checksum.h>
  65
  66 /* Forward declarations for private helpers. */
  67 static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
  68                                            struct sctp_chunk *chunk);
  69 static void sctp_packet_append_data(struct sctp_packet *packet,
  70                                            struct sctp_chunk *chunk);
  71 static sctp_xmit_t sctp_packet_will_fit(struct sctp_packet *packet,
  72                                         struct sctp_chunk *chunk,
  73                                         u16 chunk_len);
  74
  75 static void sctp_packet_reset(struct sctp_packet *packet)
  76 {
  77         packet->size = packet->overhead;
  78         packet->has_cookie_echo = 0;
  79         packet->has_sack = 0;
  80         packet->has_data = 0;
  81         packet->has_auth = 0;
  82         packet->ipfragok = 0;
  83         packet->auth = NULL;
  84 }
  85
  86 /* Config a packet.
  87  * This appears to be a followup set of initializations.
  88  */
  89 struct sctp_packet *sctp_packet_config(struct sctp_packet *packet,
  90                                        __u32 vtag, int ecn_capable)
  91 {
  92         struct sctp_chunk *chunk = NULL;
  93
  94         SCTP_DEBUG_PRINTK("%s: packet:%p vtag:0x%x\n", __func__,
  95                           packet, vtag);
  96
  97         packet->vtag = vtag;
  98
  99         if (ecn_capable && sctp_packet_empty(packet)) {
 100                 chunk = sctp_get_ecne_prepend(packet->transport->asoc);
 101
 102                 /* If there a is a prepend chunk stick it on the list before
 103                  * any other chunks get appended.
 104                  */
 105                 if (chunk)
 106                         sctp_packet_append_chunk(packet, chunk);
 107         }
 108
 109         return packet;
 110 }
 111
 112 /* Initialize the packet structure. */
 113 struct sctp_packet *sctp_packet_init(struct sctp_packet *packet,
 114                                      struct sctp_transport *transport,
 115                                      __u16 sport, __u16 dport)
 116 {
 117         struct sctp_association *asoc = transport->asoc;
 118         size_t overhead;
 119
 120         SCTP_DEBUG_PRINTK("%s: packet:%p transport:%p\n", __func__,
 121                           packet, transport);
 122
 123         packet->transport = transport;
 124         packet->source_port = sport;
 125         packet->destination_port = dport;
 126         INIT_LIST_HEAD(&packet->chunk_list);
 127         if (asoc) {
 128                 struct sctp_sock *sp = sctp_sk(asoc->base.sk);
 129                 overhead = sp->pf->af->net_header_len;
 130         } else {
 131                 overhead = sizeof(struct ipv6hdr);
 132         }
 133         overhead += sizeof(struct sctphdr);
 134         packet->overhead = overhead;
 135         sctp_packet_reset(packet);
 136         packet->vtag = 0;
 137         packet->malloced = 0;
 138         return packet;
 139 }
 140
 141 /* Free a packet.  */
 142 void sctp_packet_free(struct sctp_packet *packet)
 143 {
 144         struct sctp_chunk *chunk, *tmp;
 145
 146         SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);
 147
 148         list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
 149                 list_del_init(&chunk->list);
 150                 sctp_chunk_free(chunk);
 151         }
 152
 153         if (packet->malloced)
 154                 kfree(packet);
 155 }
 156
 157 /* This routine tries to append the chunk to the offered packet. If adding
 158  * the chunk causes the packet to exceed the path MTU and COOKIE_ECHO chunk
 159  * is not present in the packet, it transmits the input packet.
 160  * Data can be bundled with a packet containing a COOKIE_ECHO chunk as long
 161  * as it can fit in the packet, but any more data that does not fit in this
 162  * packet can be sent only after receiving the COOKIE_ACK.
 163  */
 164 sctp_xmit_t sctp_packet_transmit_chunk(struct sctp_packet *packet,
 165                                        struct sctp_chunk *chunk,
 166                                        int one_packet)
 167 {
 168         sctp_xmit_t retval;
 169         int error = 0;
 170
 171         SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__,
 172                           packet, chunk);
 173
 174         switch ((retval = (sctp_packet_append_chunk(packet, chunk)))) {
 175         case SCTP_XMIT_PMTU_FULL:
 176                 if (!packet->has_cookie_echo) {
 177                         error = sctp_packet_transmit(packet);
 178                         if (error < 0)
 179                                 chunk->skb->sk->sk_err = -error;
 180
 181                         /* If we have an empty packet, then we can NOT ever
 182                          * return PMTU_FULL.
 183                          */
 184                         if (!one_packet)
 185                                 retval = sctp_packet_append_chunk(packet,
 186                                                                   chunk);
 187                 }
 188                 break;
 189
 190         case SCTP_XMIT_RWND_FULL:
 191         case SCTP_XMIT_OK:
 192         case SCTP_XMIT_NAGLE_DELAY:
 193                 break;
 194         }
 195
 196         return retval;
 197 }
 198
 199 /* Try to bundle an auth chunk into the packet. */
 200 static sctp_xmit_t sctp_packet_bundle_auth(struct sctp_packet *pkt,
 201                                            struct sctp_chunk *chunk)
 202 {
 203         struct sctp_association *asoc = pkt->transport->asoc;
 204         struct sctp_chunk *auth;
 205         sctp_xmit_t retval = SCTP_XMIT_OK;
 206
 207         /* if we don't have an association, we can't do authentication */
 208         if (!asoc)
 209                 return retval;
 210
 211         /* See if this is an auth chunk we are bundling or if
 212          * auth is already bundled.
 213          */
 214         if (chunk->chunk_hdr->type == SCTP_CID_AUTH || pkt->has_auth)
 215                 return retval;
 216
 217         /* if the peer did not request this chunk to be authenticated,
 218          * don't do it
 219          */
 220         if (!chunk->auth)
 221                 return retval;
 222
 223         auth = sctp_make_auth(asoc);
 224         if (!auth)
 225                 return retval;
 226
 227         retval = sctp_packet_append_chunk(pkt, auth);
 228
 229         return retval;
 230 }
 231
 232 /* Try to bundle a SACK with the packet. */
 233 static sctp_xmit_t sctp_packet_bundle_sack(struct sctp_packet *pkt,
 234                                            struct sctp_chunk *chunk)
 235 {
 236         sctp_xmit_t retval = SCTP_XMIT_OK;
 237
 238         /* If sending DATA and haven't aleady bundled a SACK, try to
 239          * bundle one in to the packet.
 240          */
 241         if (sctp_chunk_is_data(chunk) && !pkt->has_sack &&
 242             !pkt->has_cookie_echo) {
 243                 struct sctp_association *asoc;
 244                 struct timer_list *timer;
 245                 asoc = pkt->transport->asoc;
 246                 timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];
 247
 248                 /* If the SACK timer is running, we have a pending SACK */
 249                 if (timer_pending(timer)) {
 250                         struct sctp_chunk *sack;
 251                         asoc->a_rwnd = asoc->rwnd;
 252                         sack = sctp_make_sack(asoc);
 253                         if (sack) {
 254                                 retval = sctp_packet_append_chunk(pkt, sack);
 255                                 asoc->peer.sack_needed = 0;
 256                                 if (del_timer(timer))
 257                                         sctp_association_put(asoc);
 258                         }
 259                 }
 260         }
 261         return retval;
 262 }
 263
 264 /* Append a chunk to the offered packet reporting back any inability to do
 265  * so.
 266  */
 267 sctp_xmit_t sctp_packet_append_chunk(struct sctp_packet *packet,
 268                                      struct sctp_chunk *chunk)
 269 {
 270         sctp_xmit_t retval = SCTP_XMIT_OK;
 271         __u16 chunk_len = WORD_ROUND(ntohs(chunk->chunk_hdr->length));
 272
 273         SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__, packet,
 274                           chunk);
 275
 276         /* Data chunks are special.  Before seeing what else we can
 277          * bundle into this packet, check to see if we are allowed to
 278          * send this DATA.
 279          */
 280         if (sctp_chunk_is_data(chunk)) {
 281                 retval = sctp_packet_can_append_data(packet, chunk);
 282                 if (retval != SCTP_XMIT_OK)
 283                         goto finish;
 284         }
 285
 286         /* Try to bundle AUTH chunk */
 287         retval = sctp_packet_bundle_auth(packet, chunk);
 288         if (retval != SCTP_XMIT_OK)
 289                 goto finish;
 290
 291         /* Try to bundle SACK chunk */
 292         retval = sctp_packet_bundle_sack(packet, chunk);
 293         if (retval != SCTP_XMIT_OK)
 294                 goto finish;
 295
 296         /* Check to see if this chunk will fit into the packet */
 297         retval = sctp_packet_will_fit(packet, chunk, chunk_len);
 298         if (retval != SCTP_XMIT_OK)
 299                 goto finish;
 300
 301         /* We believe that this chunk is OK to add to the packet */
 302         switch (chunk->chunk_hdr->type) {
 303             case SCTP_CID_DATA:
 304                 /* Account for the data being in the packet */
 305                 sctp_packet_append_data(packet, chunk);
 306                 /* Disallow SACK bundling after DATA. */
 307                 packet->has_sack = 1;
 308                 /* Disallow AUTH bundling after DATA */
 309                 packet->has_auth = 1;
 310                 /* Let it be knows that packet has DATA in it */
 311                 packet->has_data = 1;
 312                 /* timestamp the chunk for rtx purposes */
 313                 chunk->sent_at = jiffies;
 314                 break;
 315             case SCTP_CID_COOKIE_ECHO:
 316                 packet->has_cookie_echo = 1;
 317                 break;
 318
 319             case SCTP_CID_SACK:
 320                 packet->has_sack = 1;
 321                 break;
 322
 323             case SCTP_CID_AUTH:
 324                 packet->has_auth = 1;
 325                 packet->auth = chunk;
 326                 break;
 327         }
 328
 329         /* It is OK to send this chunk.  */
 330         list_add_tail(&chunk->list, &packet->chunk_list);
 331         packet->size += chunk_len;
 332         chunk->transport = packet->transport;
 333 finish:
 334         return retval;
 335 }
 336
 337 /* All packets are sent to the network through this function from
 338  * sctp_outq_tail().
 339  *
 340  * The return value is a normal kernel error return value.
 341  */
 342 int sctp_packet_transmit(struct sctp_packet *packet)
 343 {
 344         struct sctp_transport *tp = packet->transport;
 345         struct sctp_association *asoc = tp->asoc;
 346         struct sctphdr *sh;
 347         struct sk_buff *nskb;
 348         struct sctp_chunk *chunk, *tmp;
 349         struct sock *sk;
 350         int err = 0;
 351         int padding;            /* How much padding do we need?  */
 352         __u8 has_data = 0;
 353         struct dst_entry *dst = tp->dst;
 354         unsigned char *auth = NULL;     /* pointer to auth in skb data */
 355         __u32 cksum_buf_len = sizeof(struct sctphdr);
 356
 357         SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);
 358
 359         /* Do NOT generate a chunkless packet. */
 360         if (list_empty(&packet->chunk_list))
 361                 return err;
 362
 363         /* Set up convenience variables... */
 364         chunk = list_entry(packet->chunk_list.next, struct sctp_chunk, list);
 365         sk = chunk->skb->sk;
 366
 367         /* Allocate the new skb.  */
 368         nskb = alloc_skb(packet->size + LL_MAX_HEADER, GFP_ATOMIC);
 369         if (!nskb)
 370                 goto nomem;
 371
 372         /* Make sure the outbound skb has enough header room reserved. */
 373         skb_reserve(nskb, packet->overhead + LL_MAX_HEADER);
 374
 375         /* Set the owning socket so that we know where to get the
 376          * destination IP address.
 377          */
 378         skb_set_owner_w(nskb, sk);
 379
 380         /* The 'obsolete' field of dst is set to 2 when a dst is freed. */
 381         if (!dst || (dst->obsolete > 1)) {
 382                 dst_release(dst);
 383                 sctp_transport_route(tp, NULL, sctp_sk(sk));
 384                 if (asoc && (asoc->param_flags & SPP_PMTUD_ENABLE)) {
 385                         sctp_assoc_sync_pmtu(asoc);
 386                 }
 387         }
 388         dst = dst_clone(tp->dst);
 389         skb_dst_set(nskb, dst);
 390         if (!dst)
 391                 goto no_route;
 392
 393         /* Build the SCTP header.  */
 394         sh = (struct sctphdr *)skb_push(nskb, sizeof(struct sctphdr));
 395         skb_reset_transport_header(nskb);
 396         sh->source = htons(packet->source_port);
 397         sh->dest   = htons(packet->destination_port);
 398
 399         /* From 6.8 Adler-32 Checksum Calculation:
 400          * After the packet is constructed (containing the SCTP common
 401          * header and one or more control or DATA chunks), the
 402          * transmitter shall:
 403          *
 404          * 1) Fill in the proper Verification Tag in the SCTP common
 405          *    header and initialize the checksum field to 0's.
 406          */
 407         sh->vtag     = htonl(packet->vtag);
 408         sh->checksum = 0;
 409
 410         /**
 411          * 6.10 Bundling
 412          *
 413          *    An endpoint bundles chunks by simply including multiple
 414          *    chunks in one outbound SCTP packet.  ...
 415          */
 416
 417         /**
 418          * 3.2  Chunk Field Descriptions
 419          *
 420          * The total length of a chunk (including Type, Length and
 421          * Value fields) MUST be a multiple of 4 bytes.  If the length
 422          * of the chunk is not a multiple of 4 bytes, the sender MUST
 423          * pad the chunk with all zero bytes and this padding is not
 424          * included in the chunk length field.  The sender should
 425          * never pad with more than 3 bytes.
 426          *
 427          * [This whole comment explains WORD_ROUND() below.]
 428          */
 429         SCTP_DEBUG_PRINTK("***sctp_transmit_packet***\n");
 430         list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
 431                 list_del_init(&chunk->list);
 432                 if (sctp_chunk_is_data(chunk)) {
 433                         /* 6.3.1 C4) When data is in flight and when allowed
 434                          * by rule C5, a new RTT measurement MUST be made each
 435                          * round trip.  Furthermore, new RTT measurements
 436                          * SHOULD be made no more than once per round-trip
 437                          * for a given destination transport address.
 438                          */
 439
 440                         if (!tp->rto_pending) {
 441                                 chunk->rtt_in_progress = 1;
 442                                 tp->rto_pending = 1;
 443                         }
 444                         has_data = 1;
 445                 }
 446
 447                 padding = WORD_ROUND(chunk->skb->len) - chunk->skb->len;
 448                 if (padding)
 449                         memset(skb_put(chunk->skb, padding), 0, padding);
 450
 451                 /* if this is the auth chunk that we are adding,
 452                  * store pointer where it will be added and put
 453                  * the auth into the packet.
 454                  */
 455                 if (chunk == packet->auth)
 456                         auth = skb_tail_pointer(nskb);
 457
 458                 cksum_buf_len += chunk->skb->len;
 459                 memcpy(skb_put(nskb, chunk->skb->len),
 460                                chunk->skb->data, chunk->skb->len);
 461
 462                 SCTP_DEBUG_PRINTK("%s %p[%s] %s 0x%x, %s %d, %s %d, %s %d\n",
 463                                   "*** Chunk", chunk,
 464                                   sctp_cname(SCTP_ST_CHUNK(
 465                                           chunk->chunk_hdr->type)),
 466                                   chunk->has_tsn ? "TSN" : "No TSN",
 467                                   chunk->has_tsn ?
 468                                   ntohl(chunk->subh.data_hdr->tsn) : 0,
 469                                   "length", ntohs(chunk->chunk_hdr->length),
 470                                   "chunk->skb->len", chunk->skb->len,
 471                                   "rtt_in_progress", chunk->rtt_in_progress);
 472
 473                 /*
 474                  * If this is a control chunk, this is our last
 475                  * reference. Free data chunks after they've been
 476                  * acknowledged or have failed.
 477                  */
 478                 if (!sctp_chunk_is_data(chunk))
 479                         sctp_chunk_free(chunk);
 480         }
 481
 482         /* SCTP-AUTH, Section 6.2
 483          *    The sender MUST calculate the MAC as described in RFC2104 [2]
 484          *    using the hash function H as described by the MAC Identifier and
 485          *    the shared association key K based on the endpoint pair shared key
 486          *    described by the shared key identifier.  The 'data' used for the
 487          *    computation of the AUTH-chunk is given by the AUTH chunk with its
 488          *    HMAC field set to zero (as shown in Figure 6) followed by all
 489          *    chunks that are placed after the AUTH chunk in the SCTP packet.
 490          */
 491         if (auth)
 492                 sctp_auth_calculate_hmac(asoc, nskb,
 493                                         (struct sctp_auth_chunk *)auth,
 494                                         GFP_ATOMIC);
 495
 496         /* 2) Calculate the Adler-32 checksum of the whole packet,
 497          *    including the SCTP common header and all the
 498          *    chunks.
 499          *
 500          * Note: Adler-32 is no longer applicable, as has been replaced
 501          * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
 502          */
 503         if (!sctp_checksum_disable &&
 504             !(dst->dev->features & (NETIF_F_NO_CSUM | NETIF_F_SCTP_CSUM))) {
 505                 __u32 crc32 = sctp_start_cksum((__u8 *)sh, cksum_buf_len);
 506
 507                 /* 3) Put the resultant value into the checksum field in the
 508                  *    common header, and leave the rest of the bits unchanged.
 509                  */
 510                 sh->checksum = sctp_end_cksum(crc32);
 511         } else {
 512                 if (dst->dev->features & NETIF_F_SCTP_CSUM) {
 513                         /* no need to seed pseudo checksum for SCTP */
 514                         nskb->ip_summed = CHECKSUM_PARTIAL;
 515                         nskb->csum_start = (skb_transport_header(nskb) -
 516                                             nskb->head);
 517                         nskb->csum_offset = offsetof(struct sctphdr, checksum);
 518                 } else {
 519                         nskb->ip_summed = CHECKSUM_UNNECESSARY;
 520                 }
 521         }
 522
 523         /* IP layer ECN support
 524          * From RFC 2481
 525          *  "The ECN-Capable Transport (ECT) bit would be set by the
 526          *   data sender to indicate that the end-points of the
 527          *   transport protocol are ECN-capable."
 528          *
 529          * Now setting the ECT bit all the time, as it should not cause
 530          * any problems protocol-wise even if our peer ignores it.
 531          *
 532          * Note: The works for IPv6 layer checks this bit too later
 533          * in transmission.  See IP6_ECN_flow_xmit().
 534          */
 535         (*tp->af_specific->ecn_capable)(nskb->sk);
 536
 537         /* Set up the IP options.  */
 538         /* BUG: not implemented
 539          * For v4 this all lives somewhere in sk->sk_opt...
 540          */
 541
 542         /* Dump that on IP!  */
 543         if (asoc && asoc->peer.last_sent_to != tp) {
 544                 /* Considering the multiple CPU scenario, this is a
 545                  * "correcter" place for last_sent_to.  --xguo
 546                  */
 547                 asoc->peer.last_sent_to = tp;
 548         }
 549
 550         if (has_data) {
 551                 struct timer_list *timer;
 552                 unsigned long timeout;
 553
 554                 /* Restart the AUTOCLOSE timer when sending data. */
 555                 if (sctp_state(asoc, ESTABLISHED) && asoc->autoclose) {
 556                         timer = &asoc->timers[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
 557                         timeout = asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
 558
 559                         if (!mod_timer(timer, jiffies + timeout))
 560                                 sctp_association_hold(asoc);
 561                 }
 562         }
 563
 564         SCTP_DEBUG_PRINTK("***sctp_transmit_packet*** skb len %d\n",
 565                           nskb->len);
 566
 567         nskb->local_df = packet->ipfragok;
 568         (*tp->af_specific->sctp_xmit)(nskb, tp);
 569
 570 out:
 571         sctp_packet_reset(packet);
 572         return err;
 573 no_route:
 574         kfree_skb(nskb);
 575         IP_INC_STATS_BH(&init_net, IPSTATS_MIB_OUTNOROUTES);
 576
 577         /* FIXME: Returning the 'err' will effect all the associations
 578          * associated with a socket, although only one of the paths of the
 579          * association is unreachable.
 580          * The real failure of a transport or association can be passed on
 581          * to the user via notifications. So setting this error may not be
 582          * required.
 583          */
 584          /* err = -EHOSTUNREACH; */
 585 err:
 586         /* Control chunks are unreliable so just drop them.  DATA chunks
 587          * will get resent or dropped later.
 588          */
 589
 590         list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
 591                 list_del_init(&chunk->list);
 592                 if (!sctp_chunk_is_data(chunk))
 593                         sctp_chunk_free(chunk);
 594         }
 595         goto out;
 596 nomem:
 597         err = -ENOMEM;
 598         goto err;
 599 }
 600
 601 /********************************************************************
 602  * 2nd Level Abstractions
 603  ********************************************************************/
 604
 605 /* This private function check to see if a chunk can be added */
 606 static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
 607                                            struct sctp_chunk *chunk)
 608 {
 609         sctp_xmit_t retval = SCTP_XMIT_OK;
 610         size_t datasize, rwnd, inflight, flight_size;
 611         struct sctp_transport *transport = packet->transport;
 612         struct sctp_association *asoc = transport->asoc;
 613         struct sctp_outq *q = &asoc->outqueue;
 614
 615         /* RFC 2960 6.1  Transmission of DATA Chunks
 616          *
 617          * A) At any given time, the data sender MUST NOT transmit new data to
 618          * any destination transport address if its peer's rwnd indicates
 619          * that the peer has no buffer space (i.e. rwnd is 0, see Section
 620          * 6.2.1).  However, regardless of the value of rwnd (including if it
 621          * is 0), the data sender can always have one DATA chunk in flight to
 622          * the receiver if allowed by cwnd (see rule B below).  This rule
 623          * allows the sender to probe for a change in rwnd that the sender
 624          * missed due to the SACK having been lost in transit from the data
 625          * receiver to the data sender.
 626          */
 627
 628         rwnd = asoc->peer.rwnd;
 629         inflight = q->outstanding_bytes;
 630         flight_size = transport->flight_size;
 631
 632         datasize = sctp_data_size(chunk);
 633
 634         if (datasize > rwnd) {
 635                 if (inflight > 0) {
 636                         /* We have (at least) one data chunk in flight,
 637                          * so we can't fall back to rule 6.1 B).
 638                          */
 639                         retval = SCTP_XMIT_RWND_FULL;
 640                         goto finish;
 641                 }
 642         }
 643
 644         /* RFC 2960 6.1  Transmission of DATA Chunks
 645          *
 646          * B) At any given time, the sender MUST NOT transmit new data
 647          * to a given transport address if it has cwnd or more bytes
 648          * of data outstanding to that transport address.
 649          */
 650         /* RFC 7.2.4 & the Implementers Guide 2.8.
 651          *
 652          * 3) ...
 653          *    When a Fast Retransmit is being performed the sender SHOULD
 654          *    ignore the value of cwnd and SHOULD NOT delay retransmission.
 655          */
 656         if (chunk->fast_retransmit != SCTP_NEED_FRTX)
 657                 if (flight_size >= transport->cwnd) {
 658                         retval = SCTP_XMIT_RWND_FULL;
 659                         goto finish;
 660                 }
 661
 662         /* Nagle's algorithm to solve small-packet problem:
 663          * Inhibit the sending of new chunks when new outgoing data arrives
 664          * if any previously transmitted data on the connection remains
 665          * unacknowledged.
 666          */
 667         if (!sctp_sk(asoc->base.sk)->nodelay && sctp_packet_empty(packet) &&
 668             inflight && sctp_state(asoc, ESTABLISHED)) {
 669                 unsigned max = transport->pathmtu - packet->overhead;
 670                 unsigned len = chunk->skb->len + q->out_qlen;
 671
 672                 /* Check whether this chunk and all the rest of pending
 673                  * data will fit or delay in hopes of bundling a full
 674                  * sized packet.
 675                  * Don't delay large message writes that may have been
 676                  * fragmeneted into small peices.
 677                  */
 678                 if ((len < max) && chunk->msg->can_delay) {
 679                         retval = SCTP_XMIT_NAGLE_DELAY;
 680                         goto finish;
 681                 }
 682         }
 683
 684 finish:
 685         return retval;
 686 }
 687
 688 /* This private function does management things when adding DATA chunk */
 689 static void sctp_packet_append_data(struct sctp_packet *packet,
 690                                 struct sctp_chunk *chunk)
 691 {
 692         struct sctp_transport *transport = packet->transport;
 693         size_t datasize = sctp_data_size(chunk);
 694         struct sctp_association *asoc = transport->asoc;
 695         u32 rwnd = asoc->peer.rwnd;
 696
 697         /* Keep track of how many bytes are in flight over this transport. */
 698         transport->flight_size += datasize;
 699
 700         /* Keep track of how many bytes are in flight to the receiver. */
 701         asoc->outqueue.outstanding_bytes += datasize;
 702
 703         /* Update our view of the receiver's rwnd. Include sk_buff overhead
 704          * while updating peer.rwnd so that it reduces the chances of a
 705          * receiver running out of receive buffer space even when receive
 706          * window is still open. This can happen when a sender is sending
 707          * sending small messages.
 708          */
 709         datasize += sizeof(struct sk_buff);
 710         if (datasize < rwnd)
 711                 rwnd -= datasize;
 712         else
 713                 rwnd = 0;
 714
 715         asoc->peer.rwnd = rwnd;
 716         /* Has been accepted for transmission. */
 717         if (!asoc->peer.prsctp_capable)
 718                 chunk->msg->can_abandon = 0;
 719         sctp_chunk_assign_tsn(chunk);
 720         sctp_chunk_assign_ssn(chunk);
 721 }
 722
 723 static sctp_xmit_t sctp_packet_will_fit(struct sctp_packet *packet,
 724                                         struct sctp_chunk *chunk,
 725                                         u16 chunk_len)
 726 {
 727         size_t psize;
 728         size_t pmtu;
 729         int too_big;
 730         sctp_xmit_t retval = SCTP_XMIT_OK;
 731
 732         psize = packet->size;
 733         pmtu  = ((packet->transport->asoc) ?
 734                 (packet->transport->asoc->pathmtu) :
 735                 (packet->transport->pathmtu));
 736
 737         too_big = (psize + chunk_len > pmtu);
 738
 739         /* Decide if we need to fragment or resubmit later. */
 740         if (too_big) {
 741                 /* It's OK to fragmet at IP level if any one of the following
 742                  * is true:
 743                  *      1. The packet is empty (meaning this chunk is greater
 744                  *         the MTU)
 745                  *      2. The chunk we are adding is a control chunk
 746                  *      3. The packet doesn't have any data in it yet and data
 747                  *      requires authentication.
 748                  */
 749                 if (sctp_packet_empty(packet) || !sctp_chunk_is_data(chunk) ||
 750                     (!packet->has_data && chunk->auth)) {
 751                         /* We no longer do re-fragmentation.
 752                          * Just fragment at the IP layer, if we
 753                          * actually hit this condition
 754                          */
 755                         packet->ipfragok = 1;
 756                 } else {
 757                         retval = SCTP_XMIT_PMTU_FULL;
 758                 }
 759         }
 760
 761         return retval;
 762 }