linux/net/sctp/output.c
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   1/* SCTP kernel implementation
   2 * (C) Copyright IBM Corp. 2001, 2004
   3 * Copyright (c) 1999-2000 Cisco, Inc.
   4 * Copyright (c) 1999-2001 Motorola, Inc.
   5 *
   6 * This file is part of the SCTP kernel implementation
   7 *
   8 * These functions handle output processing.
   9 *
  10 * This SCTP implementation is free software;
  11 * you can redistribute it and/or modify it under the terms of
  12 * the GNU General Public License as published by
  13 * the Free Software Foundation; either version 2, or (at your option)
  14 * any later version.
  15 *
  16 * This SCTP implementation is distributed in the hope that it
  17 * will be useful, but WITHOUT ANY WARRANTY; without even the implied
  18 *                 ************************
  19 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  20 * See the GNU General Public License for more details.
  21 *
  22 * You should have received a copy of the GNU General Public License
  23 * along with GNU CC; see the file COPYING.  If not, write to
  24 * the Free Software Foundation, 59 Temple Place - Suite 330,
  25 * Boston, MA 02111-1307, USA.
  26 *
  27 * Please send any bug reports or fixes you make to the
  28 * email address(es):
  29 *    lksctp developers <lksctp-developers@lists.sourceforge.net>
  30 *
  31 * Or submit a bug report through the following website:
  32 *    http://www.sf.net/projects/lksctp
  33 *
  34 * Written or modified by:
  35 *    La Monte H.P. Yarroll <piggy@acm.org>
  36 *    Karl Knutson          <karl@athena.chicago.il.us>
  37 *    Jon Grimm             <jgrimm@austin.ibm.com>
  38 *    Sridhar Samudrala     <sri@us.ibm.com>
  39 *
  40 * Any bugs reported given to us we will try to fix... any fixes shared will
  41 * be incorporated into the next SCTP release.
  42 */
  43
  44#include <linux/types.h>
  45#include <linux/kernel.h>
  46#include <linux/wait.h>
  47#include <linux/time.h>
  48#include <linux/ip.h>
  49#include <linux/ipv6.h>
  50#include <linux/init.h>
  51#include <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. */
  65static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
  66                                           struct sctp_chunk *chunk);
  67static void sctp_packet_append_data(struct sctp_packet *packet,
  68                                           struct sctp_chunk *chunk);
  69static sctp_xmit_t sctp_packet_will_fit(struct sctp_packet *packet,
  70                                        struct sctp_chunk *chunk,
  71                                        u16 chunk_len);
  72
  73static 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 */
  87struct 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. */
 112struct 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.  */
 141void 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 */
 163sctp_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. */
 199static 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. */
 232static 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 */
 266sctp_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;
 332finish:
 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 */
 341int 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
 569out:
 570        sctp_packet_reset(packet);
 571        return err;
 572no_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; */
 584err:
 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;
 595nomem:
 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 */
 605static 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
 683finish:
 684        return retval;
 685}
 686
 687/* This private function does management things when adding DATA chunk */
 688static 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
 722static 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}
 762