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