net/sctp/transport.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* SCTP kernel implementation
   3  * Copyright (c) 1999-2000 Cisco, Inc.
   4  * Copyright (c) 1999-2001 Motorola, Inc.
   5  * Copyright (c) 2001-2003 International Business Machines Corp.
   6  * Copyright (c) 2001 Intel Corp.
   7  * Copyright (c) 2001 La Monte H.P. Yarroll
   8  *
   9  * This file is part of the SCTP kernel implementation
  10  *
  11  * This module provides the abstraction for an SCTP transport representing
  12  * a remote transport address.  For local transport addresses, we just use
  13  * union sctp_addr.
  14  *
  15  * Please send any bug reports or fixes you make to the
  16  * email address(es):
  17  *    lksctp developers <linux-sctp@vger.kernel.org>
  18  *
  19  * Written or modified by:
  20  *    La Monte H.P. Yarroll <piggy@acm.org>
  21  *    Karl Knutson          <karl@athena.chicago.il.us>
  22  *    Jon Grimm             <jgrimm@us.ibm.com>
  23  *    Xingang Guo           <xingang.guo@intel.com>
  24  *    Hui Huang             <hui.huang@nokia.com>
  25  *    Sridhar Samudrala     <sri@us.ibm.com>
  26  *    Ardelle Fan           <ardelle.fan@intel.com>
  27  */
  28
  29 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  30
  31 #include <linux/slab.h>
  32 #include <linux/types.h>
  33 #include <linux/random.h>
  34 #include <net/sctp/sctp.h>
  35 #include <net/sctp/sm.h>
  36
  37 /* 1st Level Abstractions.  */
  38
  39 /* Initialize a new transport from provided memory.  */
  40 static struct sctp_transport *sctp_transport_init(struct net *net,
  41                                                   struct sctp_transport *peer,
  42                                                   const union sctp_addr *addr,
  43                                                   gfp_t gfp)
  44 {
  45         /* Copy in the address.  */
  46         peer->af_specific = sctp_get_af_specific(addr->sa.sa_family);
  47         memcpy(&peer->ipaddr, addr, peer->af_specific->sockaddr_len);
  48         memset(&peer->saddr, 0, sizeof(union sctp_addr));
  49
  50         peer->sack_generation = 0;
  51
  52         /* From 6.3.1 RTO Calculation:
  53          *
  54          * C1) Until an RTT measurement has been made for a packet sent to the
  55          * given destination transport address, set RTO to the protocol
  56          * parameter 'RTO.Initial'.
  57          */
  58         peer->rto = msecs_to_jiffies(net->sctp.rto_initial);
  59
  60         peer->last_time_heard = 0;
  61         peer->last_time_ecne_reduced = jiffies;
  62
  63         peer->param_flags = SPP_HB_DISABLE |
  64                             SPP_PMTUD_ENABLE |
  65                             SPP_SACKDELAY_ENABLE;
  66
  67         /* Initialize the default path max_retrans.  */
  68         peer->pathmaxrxt  = net->sctp.max_retrans_path;
  69         peer->pf_retrans  = net->sctp.pf_retrans;
  70
  71         INIT_LIST_HEAD(&peer->transmitted);
  72         INIT_LIST_HEAD(&peer->send_ready);
  73         INIT_LIST_HEAD(&peer->transports);
  74
  75         timer_setup(&peer->T3_rtx_timer, sctp_generate_t3_rtx_event, 0);
  76         timer_setup(&peer->hb_timer, sctp_generate_heartbeat_event, 0);
  77         timer_setup(&peer->reconf_timer, sctp_generate_reconf_event, 0);
  78         timer_setup(&peer->probe_timer, sctp_generate_probe_event, 0);
  79         timer_setup(&peer->proto_unreach_timer,
  80                     sctp_generate_proto_unreach_event, 0);
  81
  82         /* Initialize the 64-bit random nonce sent with heartbeat. */
  83         get_random_bytes(&peer->hb_nonce, sizeof(peer->hb_nonce));
  84
  85         refcount_set(&peer->refcnt, 1);
  86
  87         return peer;
  88 }
  89
  90 /* Allocate and initialize a new transport.  */
  91 struct sctp_transport *sctp_transport_new(struct net *net,
  92                                           const union sctp_addr *addr,
  93                                           gfp_t gfp)
  94 {
  95         struct sctp_transport *transport;
  96
  97         transport = kzalloc(sizeof(*transport), gfp);
  98         if (!transport)
  99                 goto fail;
 100
 101         if (!sctp_transport_init(net, transport, addr, gfp))
 102                 goto fail_init;
 103
 104         SCTP_DBG_OBJCNT_INC(transport);
 105
 106         return transport;
 107
 108 fail_init:
 109         kfree(transport);
 110
 111 fail:
 112         return NULL;
 113 }
 114
 115 /* This transport is no longer needed.  Free up if possible, or
 116  * delay until it last reference count.
 117  */
 118 void sctp_transport_free(struct sctp_transport *transport)
 119 {
 120         /* Try to delete the heartbeat timer.  */
 121         if (del_timer(&transport->hb_timer))
 122                 sctp_transport_put(transport);
 123
 124         /* Delete the T3_rtx timer if it's active.
 125          * There is no point in not doing this now and letting
 126          * structure hang around in memory since we know
 127          * the transport is going away.
 128          */
 129         if (del_timer(&transport->T3_rtx_timer))
 130                 sctp_transport_put(transport);
 131
 132         if (del_timer(&transport->reconf_timer))
 133                 sctp_transport_put(transport);
 134
 135         if (del_timer(&transport->probe_timer))
 136                 sctp_transport_put(transport);
 137
 138         /* Delete the ICMP proto unreachable timer if it's active. */
 139         if (del_timer(&transport->proto_unreach_timer))
 140                 sctp_transport_put(transport);
 141
 142         sctp_transport_put(transport);
 143 }
 144
 145 static void sctp_transport_destroy_rcu(struct rcu_head *head)
 146 {
 147         struct sctp_transport *transport;
 148
 149         transport = container_of(head, struct sctp_transport, rcu);
 150
 151         dst_release(transport->dst);
 152         kfree(transport);
 153         SCTP_DBG_OBJCNT_DEC(transport);
 154 }
 155
 156 /* Destroy the transport data structure.
 157  * Assumes there are no more users of this structure.
 158  */
 159 static void sctp_transport_destroy(struct sctp_transport *transport)
 160 {
 161         if (unlikely(refcount_read(&transport->refcnt))) {
 162                 WARN(1, "Attempt to destroy undead transport %p!\n", transport);
 163                 return;
 164         }
 165
 166         sctp_packet_free(&transport->packet);
 167
 168         if (transport->asoc)
 169                 sctp_association_put(transport->asoc);
 170
 171         call_rcu(&transport->rcu, sctp_transport_destroy_rcu);
 172 }
 173
 174 /* Start T3_rtx timer if it is not already running and update the heartbeat
 175  * timer.  This routine is called every time a DATA chunk is sent.
 176  */
 177 void sctp_transport_reset_t3_rtx(struct sctp_transport *transport)
 178 {
 179         /* RFC 2960 6.3.2 Retransmission Timer Rules
 180          *
 181          * R1) Every time a DATA chunk is sent to any address(including a
 182          * retransmission), if the T3-rtx timer of that address is not running
 183          * start it running so that it will expire after the RTO of that
 184          * address.
 185          */
 186
 187         if (!timer_pending(&transport->T3_rtx_timer))
 188                 if (!mod_timer(&transport->T3_rtx_timer,
 189                                jiffies + transport->rto))
 190                         sctp_transport_hold(transport);
 191 }
 192
 193 void sctp_transport_reset_hb_timer(struct sctp_transport *transport)
 194 {
 195         unsigned long expires;
 196
 197         /* When a data chunk is sent, reset the heartbeat interval.  */
 198         expires = jiffies + sctp_transport_timeout(transport);
 199         if (!mod_timer(&transport->hb_timer,
 200                        expires + get_random_u32_below(transport->rto)))
 201                 sctp_transport_hold(transport);
 202 }
 203
 204 void sctp_transport_reset_reconf_timer(struct sctp_transport *transport)
 205 {
 206         if (!timer_pending(&transport->reconf_timer))
 207                 if (!mod_timer(&transport->reconf_timer,
 208                                jiffies + transport->rto))
 209                         sctp_transport_hold(transport);
 210 }
 211
 212 void sctp_transport_reset_probe_timer(struct sctp_transport *transport)
 213 {
 214         if (!mod_timer(&transport->probe_timer,
 215                        jiffies + transport->probe_interval))
 216                 sctp_transport_hold(transport);
 217 }
 218
 219 void sctp_transport_reset_raise_timer(struct sctp_transport *transport)
 220 {
 221         if (!mod_timer(&transport->probe_timer,
 222                        jiffies + transport->probe_interval * 30))
 223                 sctp_transport_hold(transport);
 224 }
 225
 226 /* This transport has been assigned to an association.
 227  * Initialize fields from the association or from the sock itself.
 228  * Register the reference count in the association.
 229  */
 230 void sctp_transport_set_owner(struct sctp_transport *transport,
 231                               struct sctp_association *asoc)
 232 {
 233         transport->asoc = asoc;
 234         sctp_association_hold(asoc);
 235 }
 236
 237 /* Initialize the pmtu of a transport. */
 238 void sctp_transport_pmtu(struct sctp_transport *transport, struct sock *sk)
 239 {
 240         /* If we don't have a fresh route, look one up */
 241         if (!transport->dst || transport->dst->obsolete) {
 242                 sctp_transport_dst_release(transport);
 243                 transport->af_specific->get_dst(transport, &transport->saddr,
 244                                                 &transport->fl, sk);
 245         }
 246
 247         if (transport->param_flags & SPP_PMTUD_DISABLE) {
 248                 struct sctp_association *asoc = transport->asoc;
 249
 250                 if (!transport->pathmtu && asoc && asoc->pathmtu)
 251                         transport->pathmtu = asoc->pathmtu;
 252                 if (transport->pathmtu)
 253                         return;
 254         }
 255
 256         if (transport->dst)
 257                 transport->pathmtu = sctp_dst_mtu(transport->dst);
 258         else
 259                 transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT;
 260
 261         sctp_transport_pl_update(transport);
 262 }
 263
 264 void sctp_transport_pl_send(struct sctp_transport *t)
 265 {
 266         if (t->pl.probe_count < SCTP_MAX_PROBES)
 267                 goto out;
 268
 269         t->pl.probe_count = 0;
 270         if (t->pl.state == SCTP_PL_BASE) {
 271                 if (t->pl.probe_size == SCTP_BASE_PLPMTU) { /* BASE_PLPMTU Confirmation Failed */
 272                         t->pl.state = SCTP_PL_ERROR; /* Base -> Error */
 273
 274                         t->pl.pmtu = SCTP_BASE_PLPMTU;
 275                         t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
 276                         sctp_assoc_sync_pmtu(t->asoc);
 277                 }
 278         } else if (t->pl.state == SCTP_PL_SEARCH) {
 279                 if (t->pl.pmtu == t->pl.probe_size) { /* Black Hole Detected */
 280                         t->pl.state = SCTP_PL_BASE;  /* Search -> Base */
 281                         t->pl.probe_size = SCTP_BASE_PLPMTU;
 282                         t->pl.probe_high = 0;
 283
 284                         t->pl.pmtu = SCTP_BASE_PLPMTU;
 285                         t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
 286                         sctp_assoc_sync_pmtu(t->asoc);
 287                 } else { /* Normal probe failure. */
 288                         t->pl.probe_high = t->pl.probe_size;
 289                         t->pl.probe_size = t->pl.pmtu;
 290                 }
 291         } else if (t->pl.state == SCTP_PL_COMPLETE) {
 292                 if (t->pl.pmtu == t->pl.probe_size) { /* Black Hole Detected */
 293                         t->pl.state = SCTP_PL_BASE;  /* Search Complete -> Base */
 294                         t->pl.probe_size = SCTP_BASE_PLPMTU;
 295
 296                         t->pl.pmtu = SCTP_BASE_PLPMTU;
 297                         t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
 298                         sctp_assoc_sync_pmtu(t->asoc);
 299                 }
 300         }
 301
 302 out:
 303         pr_debug("%s: PLPMTUD: transport: %p, state: %d, pmtu: %d, size: %d, high: %d\n",
 304                  __func__, t, t->pl.state, t->pl.pmtu, t->pl.probe_size, t->pl.probe_high);
 305         t->pl.probe_count++;
 306 }
 307
 308 bool sctp_transport_pl_recv(struct sctp_transport *t)
 309 {
 310         pr_debug("%s: PLPMTUD: transport: %p, state: %d, pmtu: %d, size: %d, high: %d\n",
 311                  __func__, t, t->pl.state, t->pl.pmtu, t->pl.probe_size, t->pl.probe_high);
 312
 313         t->pl.pmtu = t->pl.probe_size;
 314         t->pl.probe_count = 0;
 315         if (t->pl.state == SCTP_PL_BASE) {
 316                 t->pl.state = SCTP_PL_SEARCH; /* Base -> Search */
 317                 t->pl.probe_size += SCTP_PL_BIG_STEP;
 318         } else if (t->pl.state == SCTP_PL_ERROR) {
 319                 t->pl.state = SCTP_PL_SEARCH; /* Error -> Search */
 320
 321                 t->pl.pmtu = t->pl.probe_size;
 322                 t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
 323                 sctp_assoc_sync_pmtu(t->asoc);
 324                 t->pl.probe_size += SCTP_PL_BIG_STEP;
 325         } else if (t->pl.state == SCTP_PL_SEARCH) {
 326                 if (!t->pl.probe_high) {
 327                         if (t->pl.probe_size < SCTP_MAX_PLPMTU) {
 328                                 t->pl.probe_size = min(t->pl.probe_size + SCTP_PL_BIG_STEP,
 329                                                        SCTP_MAX_PLPMTU);
 330                                 return false;
 331                         }
 332                         t->pl.probe_high = SCTP_MAX_PLPMTU;
 333                 }
 334                 t->pl.probe_size += SCTP_PL_MIN_STEP;
 335                 if (t->pl.probe_size >= t->pl.probe_high) {
 336                         t->pl.probe_high = 0;
 337                         t->pl.state = SCTP_PL_COMPLETE; /* Search -> Search Complete */
 338
 339                         t->pl.probe_size = t->pl.pmtu;
 340                         t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
 341                         sctp_assoc_sync_pmtu(t->asoc);
 342                         sctp_transport_reset_raise_timer(t);
 343                 }
 344         } else if (t->pl.state == SCTP_PL_COMPLETE) {
 345                 /* Raise probe_size again after 30 * interval in Search Complete */
 346                 t->pl.state = SCTP_PL_SEARCH; /* Search Complete -> Search */
 347                 t->pl.probe_size = min(t->pl.probe_size + SCTP_PL_MIN_STEP, SCTP_MAX_PLPMTU);
 348         }
 349
 350         return t->pl.state == SCTP_PL_COMPLETE;
 351 }
 352
 353 static bool sctp_transport_pl_toobig(struct sctp_transport *t, u32 pmtu)
 354 {
 355         pr_debug("%s: PLPMTUD: transport: %p, state: %d, pmtu: %d, size: %d, ptb: %d\n",
 356                  __func__, t, t->pl.state, t->pl.pmtu, t->pl.probe_size, pmtu);
 357
 358         if (pmtu < SCTP_MIN_PLPMTU || pmtu >= t->pl.probe_size)
 359                 return false;
 360
 361         if (t->pl.state == SCTP_PL_BASE) {
 362                 if (pmtu >= SCTP_MIN_PLPMTU && pmtu < SCTP_BASE_PLPMTU) {
 363                         t->pl.state = SCTP_PL_ERROR; /* Base -> Error */
 364
 365                         t->pl.pmtu = SCTP_BASE_PLPMTU;
 366                         t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
 367                         return true;
 368                 }
 369         } else if (t->pl.state == SCTP_PL_SEARCH) {
 370                 if (pmtu >= SCTP_BASE_PLPMTU && pmtu < t->pl.pmtu) {
 371                         t->pl.state = SCTP_PL_BASE;  /* Search -> Base */
 372                         t->pl.probe_size = SCTP_BASE_PLPMTU;
 373                         t->pl.probe_count = 0;
 374
 375                         t->pl.probe_high = 0;
 376                         t->pl.pmtu = SCTP_BASE_PLPMTU;
 377                         t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
 378                         return true;
 379                 } else if (pmtu > t->pl.pmtu && pmtu < t->pl.probe_size) {
 380                         t->pl.probe_size = pmtu;
 381                         t->pl.probe_count = 0;
 382                 }
 383         } else if (t->pl.state == SCTP_PL_COMPLETE) {
 384                 if (pmtu >= SCTP_BASE_PLPMTU && pmtu < t->pl.pmtu) {
 385                         t->pl.state = SCTP_PL_BASE;  /* Complete -> Base */
 386                         t->pl.probe_size = SCTP_BASE_PLPMTU;
 387                         t->pl.probe_count = 0;
 388
 389                         t->pl.probe_high = 0;
 390                         t->pl.pmtu = SCTP_BASE_PLPMTU;
 391                         t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
 392                         sctp_transport_reset_probe_timer(t);
 393                         return true;
 394                 }
 395         }
 396
 397         return false;
 398 }
 399
 400 bool sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu)
 401 {
 402         struct sock *sk = t->asoc->base.sk;
 403         struct dst_entry *dst;
 404         bool change = true;
 405
 406         if (unlikely(pmtu < SCTP_DEFAULT_MINSEGMENT)) {
 407                 pr_warn_ratelimited("%s: Reported pmtu %d too low, using default minimum of %d\n",
 408                                     __func__, pmtu, SCTP_DEFAULT_MINSEGMENT);
 409                 /* Use default minimum segment instead */
 410                 pmtu = SCTP_DEFAULT_MINSEGMENT;
 411         }
 412         pmtu = SCTP_TRUNC4(pmtu);
 413
 414         if (sctp_transport_pl_enabled(t))
 415                 return sctp_transport_pl_toobig(t, pmtu - sctp_transport_pl_hlen(t));
 416
 417         dst = sctp_transport_dst_check(t);
 418         if (dst) {
 419                 struct sctp_pf *pf = sctp_get_pf_specific(dst->ops->family);
 420                 union sctp_addr addr;
 421
 422                 pf->af->from_sk(&addr, sk);
 423                 pf->to_sk_daddr(&t->ipaddr, sk);
 424                 dst->ops->update_pmtu(dst, sk, NULL, pmtu, true);
 425                 pf->to_sk_daddr(&addr, sk);
 426
 427                 dst = sctp_transport_dst_check(t);
 428         }
 429
 430         if (!dst) {
 431                 t->af_specific->get_dst(t, &t->saddr, &t->fl, sk);
 432                 dst = t->dst;
 433         }
 434
 435         if (dst) {
 436                 /* Re-fetch, as under layers may have a higher minimum size */
 437                 pmtu = sctp_dst_mtu(dst);
 438                 change = t->pathmtu != pmtu;
 439         }
 440         t->pathmtu = pmtu;
 441
 442         return change;
 443 }
 444
 445 /* Caches the dst entry and source address for a transport's destination
 446  * address.
 447  */
 448 void sctp_transport_route(struct sctp_transport *transport,
 449                           union sctp_addr *saddr, struct sctp_sock *opt)
 450 {
 451         struct sctp_association *asoc = transport->asoc;
 452         struct sctp_af *af = transport->af_specific;
 453
 454         sctp_transport_dst_release(transport);
 455         af->get_dst(transport, saddr, &transport->fl, sctp_opt2sk(opt));
 456
 457         if (saddr)
 458                 memcpy(&transport->saddr, saddr, sizeof(union sctp_addr));
 459         else
 460                 af->get_saddr(opt, transport, &transport->fl);
 461
 462         sctp_transport_pmtu(transport, sctp_opt2sk(opt));
 463
 464         /* Initialize sk->sk_rcv_saddr, if the transport is the
 465          * association's active path for getsockname().
 466          */
 467         if (transport->dst && asoc &&
 468             (!asoc->peer.primary_path || transport == asoc->peer.active_path))
 469                 opt->pf->to_sk_saddr(&transport->saddr, asoc->base.sk);
 470 }
 471
 472 /* Hold a reference to a transport.  */
 473 int sctp_transport_hold(struct sctp_transport *transport)
 474 {
 475         return refcount_inc_not_zero(&transport->refcnt);
 476 }
 477
 478 /* Release a reference to a transport and clean up
 479  * if there are no more references.
 480  */
 481 void sctp_transport_put(struct sctp_transport *transport)
 482 {
 483         if (refcount_dec_and_test(&transport->refcnt))
 484                 sctp_transport_destroy(transport);
 485 }
 486
 487 /* Update transport's RTO based on the newly calculated RTT. */
 488 void sctp_transport_update_rto(struct sctp_transport *tp, __u32 rtt)
 489 {
 490         if (unlikely(!tp->rto_pending))
 491                 /* We should not be doing any RTO updates unless rto_pending is set.  */
 492                 pr_debug("%s: rto_pending not set on transport %p!\n", __func__, tp);
 493
 494         if (tp->rttvar || tp->srtt) {
 495                 struct net *net = tp->asoc->base.net;
 496                 /* 6.3.1 C3) When a new RTT measurement R' is made, set
 497                  * RTTVAR <- (1 - RTO.Beta) * RTTVAR + RTO.Beta * |SRTT - R'|
 498                  * SRTT <- (1 - RTO.Alpha) * SRTT + RTO.Alpha * R'
 499                  */
 500
 501                 /* Note:  The above algorithm has been rewritten to
 502                  * express rto_beta and rto_alpha as inverse powers
 503                  * of two.
 504                  * For example, assuming the default value of RTO.Alpha of
 505                  * 1/8, rto_alpha would be expressed as 3.
 506                  */
 507                 tp->rttvar = tp->rttvar - (tp->rttvar >> net->sctp.rto_beta)
 508                         + (((__u32)abs((__s64)tp->srtt - (__s64)rtt)) >> net->sctp.rto_beta);
 509                 tp->srtt = tp->srtt - (tp->srtt >> net->sctp.rto_alpha)
 510                         + (rtt >> net->sctp.rto_alpha);
 511         } else {
 512                 /* 6.3.1 C2) When the first RTT measurement R is made, set
 513                  * SRTT <- R, RTTVAR <- R/2.
 514                  */
 515                 tp->srtt = rtt;
 516                 tp->rttvar = rtt >> 1;
 517         }
 518
 519         /* 6.3.1 G1) Whenever RTTVAR is computed, if RTTVAR = 0, then
 520          * adjust RTTVAR <- G, where G is the CLOCK GRANULARITY.
 521          */
 522         if (tp->rttvar == 0)
 523                 tp->rttvar = SCTP_CLOCK_GRANULARITY;
 524
 525         /* 6.3.1 C3) After the computation, update RTO <- SRTT + 4 * RTTVAR. */
 526         tp->rto = tp->srtt + (tp->rttvar << 2);
 527
 528         /* 6.3.1 C6) Whenever RTO is computed, if it is less than RTO.Min
 529          * seconds then it is rounded up to RTO.Min seconds.
 530          */
 531         if (tp->rto < tp->asoc->rto_min)
 532                 tp->rto = tp->asoc->rto_min;
 533
 534         /* 6.3.1 C7) A maximum value may be placed on RTO provided it is
 535          * at least RTO.max seconds.
 536          */
 537         if (tp->rto > tp->asoc->rto_max)
 538                 tp->rto = tp->asoc->rto_max;
 539
 540         sctp_max_rto(tp->asoc, tp);
 541         tp->rtt = rtt;
 542
 543         /* Reset rto_pending so that a new RTT measurement is started when a
 544          * new data chunk is sent.
 545          */
 546         tp->rto_pending = 0;
 547
 548         pr_debug("%s: transport:%p, rtt:%d, srtt:%d rttvar:%d, rto:%ld\n",
 549                  __func__, tp, rtt, tp->srtt, tp->rttvar, tp->rto);
 550 }
 551
 552 /* This routine updates the transport's cwnd and partial_bytes_acked
 553  * parameters based on the bytes acked in the received SACK.
 554  */
 555 void sctp_transport_raise_cwnd(struct sctp_transport *transport,
 556                                __u32 sack_ctsn, __u32 bytes_acked)
 557 {
 558         struct sctp_association *asoc = transport->asoc;
 559         __u32 cwnd, ssthresh, flight_size, pba, pmtu;
 560
 561         cwnd = transport->cwnd;
 562         flight_size = transport->flight_size;
 563
 564         /* See if we need to exit Fast Recovery first */
 565         if (asoc->fast_recovery &&
 566             TSN_lte(asoc->fast_recovery_exit, sack_ctsn))
 567                 asoc->fast_recovery = 0;
 568
 569         ssthresh = transport->ssthresh;
 570         pba = transport->partial_bytes_acked;
 571         pmtu = transport->asoc->pathmtu;
 572
 573         if (cwnd <= ssthresh) {
 574                 /* RFC 4960 7.2.1
 575                  * o  When cwnd is less than or equal to ssthresh, an SCTP
 576                  *    endpoint MUST use the slow-start algorithm to increase
 577                  *    cwnd only if the current congestion window is being fully
 578                  *    utilized, an incoming SACK advances the Cumulative TSN
 579                  *    Ack Point, and the data sender is not in Fast Recovery.
 580                  *    Only when these three conditions are met can the cwnd be
 581                  *    increased; otherwise, the cwnd MUST not be increased.
 582                  *    If these conditions are met, then cwnd MUST be increased
 583                  *    by, at most, the lesser of 1) the total size of the
 584                  *    previously outstanding DATA chunk(s) acknowledged, and
 585                  *    2) the destination's path MTU.  This upper bound protects
 586                  *    against the ACK-Splitting attack outlined in [SAVAGE99].
 587                  */
 588                 if (asoc->fast_recovery)
 589                         return;
 590
 591                 /* The appropriate cwnd increase algorithm is performed
 592                  * if, and only if the congestion window is being fully
 593                  * utilized.  Note that RFC4960 Errata 3.22 removed the
 594                  * other condition on ctsn moving.
 595                  */
 596                 if (flight_size < cwnd)
 597                         return;
 598
 599                 if (bytes_acked > pmtu)
 600                         cwnd += pmtu;
 601                 else
 602                         cwnd += bytes_acked;
 603
 604                 pr_debug("%s: slow start: transport:%p, bytes_acked:%d, "
 605                          "cwnd:%d, ssthresh:%d, flight_size:%d, pba:%d\n",
 606                          __func__, transport, bytes_acked, cwnd, ssthresh,
 607                          flight_size, pba);
 608         } else {
 609                 /* RFC 2960 7.2.2 Whenever cwnd is greater than ssthresh,
 610                  * upon each SACK arrival, increase partial_bytes_acked
 611                  * by the total number of bytes of all new chunks
 612                  * acknowledged in that SACK including chunks
 613                  * acknowledged by the new Cumulative TSN Ack and by Gap
 614                  * Ack Blocks. (updated by RFC4960 Errata 3.22)
 615                  *
 616                  * When partial_bytes_acked is greater than cwnd and
 617                  * before the arrival of the SACK the sender had less
 618                  * bytes of data outstanding than cwnd (i.e., before
 619                  * arrival of the SACK, flightsize was less than cwnd),
 620                  * reset partial_bytes_acked to cwnd. (RFC 4960 Errata
 621                  * 3.26)
 622                  *
 623                  * When partial_bytes_acked is equal to or greater than
 624                  * cwnd and before the arrival of the SACK the sender
 625                  * had cwnd or more bytes of data outstanding (i.e.,
 626                  * before arrival of the SACK, flightsize was greater
 627                  * than or equal to cwnd), partial_bytes_acked is reset
 628                  * to (partial_bytes_acked - cwnd). Next, cwnd is
 629                  * increased by MTU. (RFC 4960 Errata 3.12)
 630                  */
 631                 pba += bytes_acked;
 632                 if (pba > cwnd && flight_size < cwnd)
 633                         pba = cwnd;
 634                 if (pba >= cwnd && flight_size >= cwnd) {
 635                         pba = pba - cwnd;
 636                         cwnd += pmtu;
 637                 }
 638
 639                 pr_debug("%s: congestion avoidance: transport:%p, "
 640                          "bytes_acked:%d, cwnd:%d, ssthresh:%d, "
 641                          "flight_size:%d, pba:%d\n", __func__,
 642                          transport, bytes_acked, cwnd, ssthresh,
 643                          flight_size, pba);
 644         }
 645
 646         transport->cwnd = cwnd;
 647         transport->partial_bytes_acked = pba;
 648 }
 649
 650 /* This routine is used to lower the transport's cwnd when congestion is
 651  * detected.
 652  */
 653 void sctp_transport_lower_cwnd(struct sctp_transport *transport,
 654                                enum sctp_lower_cwnd reason)
 655 {
 656         struct sctp_association *asoc = transport->asoc;
 657
 658         switch (reason) {
 659         case SCTP_LOWER_CWND_T3_RTX:
 660                 /* RFC 2960 Section 7.2.3, sctpimpguide
 661                  * When the T3-rtx timer expires on an address, SCTP should
 662                  * perform slow start by:
 663                  *      ssthresh = max(cwnd/2, 4*MTU)
 664                  *      cwnd = 1*MTU
 665                  *      partial_bytes_acked = 0
 666                  */
 667                 transport->ssthresh = max(transport->cwnd/2,
 668                                           4*asoc->pathmtu);
 669                 transport->cwnd = asoc->pathmtu;
 670
 671                 /* T3-rtx also clears fast recovery */
 672                 asoc->fast_recovery = 0;
 673                 break;
 674
 675         case SCTP_LOWER_CWND_FAST_RTX:
 676                 /* RFC 2960 7.2.4 Adjust the ssthresh and cwnd of the
 677                  * destination address(es) to which the missing DATA chunks
 678                  * were last sent, according to the formula described in
 679                  * Section 7.2.3.
 680                  *
 681                  * RFC 2960 7.2.3, sctpimpguide Upon detection of packet
 682                  * losses from SACK (see Section 7.2.4), An endpoint
 683                  * should do the following:
 684                  *      ssthresh = max(cwnd/2, 4*MTU)
 685                  *      cwnd = ssthresh
 686                  *      partial_bytes_acked = 0
 687                  */
 688                 if (asoc->fast_recovery)
 689                         return;
 690
 691                 /* Mark Fast recovery */
 692                 asoc->fast_recovery = 1;
 693                 asoc->fast_recovery_exit = asoc->next_tsn - 1;
 694
 695                 transport->ssthresh = max(transport->cwnd/2,
 696                                           4*asoc->pathmtu);
 697                 transport->cwnd = transport->ssthresh;
 698                 break;
 699
 700         case SCTP_LOWER_CWND_ECNE:
 701                 /* RFC 2481 Section 6.1.2.
 702                  * If the sender receives an ECN-Echo ACK packet
 703                  * then the sender knows that congestion was encountered in the
 704                  * network on the path from the sender to the receiver. The
 705                  * indication of congestion should be treated just as a
 706                  * congestion loss in non-ECN Capable TCP. That is, the TCP
 707                  * source halves the congestion window "cwnd" and reduces the
 708                  * slow start threshold "ssthresh".
 709                  * A critical condition is that TCP does not react to
 710                  * congestion indications more than once every window of
 711                  * data (or more loosely more than once every round-trip time).
 712                  */
 713                 if (time_after(jiffies, transport->last_time_ecne_reduced +
 714                                         transport->rtt)) {
 715                         transport->ssthresh = max(transport->cwnd/2,
 716                                                   4*asoc->pathmtu);
 717                         transport->cwnd = transport->ssthresh;
 718                         transport->last_time_ecne_reduced = jiffies;
 719                 }
 720                 break;
 721
 722         case SCTP_LOWER_CWND_INACTIVE:
 723                 /* RFC 2960 Section 7.2.1, sctpimpguide
 724                  * When the endpoint does not transmit data on a given
 725                  * transport address, the cwnd of the transport address
 726                  * should be adjusted to max(cwnd/2, 4*MTU) per RTO.
 727                  * NOTE: Although the draft recommends that this check needs
 728                  * to be done every RTO interval, we do it every hearbeat
 729                  * interval.
 730                  */
 731                 transport->cwnd = max(transport->cwnd/2,
 732                                          4*asoc->pathmtu);
 733                 /* RFC 4960 Errata 3.27.2: also adjust sshthresh */
 734                 transport->ssthresh = transport->cwnd;
 735                 break;
 736         }
 737
 738         transport->partial_bytes_acked = 0;
 739
 740         pr_debug("%s: transport:%p, reason:%d, cwnd:%d, ssthresh:%d\n",
 741                  __func__, transport, reason, transport->cwnd,
 742                  transport->ssthresh);
 743 }
 744
 745 /* Apply Max.Burst limit to the congestion window:
 746  * sctpimpguide-05 2.14.2
 747  * D) When the time comes for the sender to
 748  * transmit new DATA chunks, the protocol parameter Max.Burst MUST
 749  * first be applied to limit how many new DATA chunks may be sent.
 750  * The limit is applied by adjusting cwnd as follows:
 751  *      if ((flightsize+ Max.Burst * MTU) < cwnd)
 752  *              cwnd = flightsize + Max.Burst * MTU
 753  */
 754
 755 void sctp_transport_burst_limited(struct sctp_transport *t)
 756 {
 757         struct sctp_association *asoc = t->asoc;
 758         u32 old_cwnd = t->cwnd;
 759         u32 max_burst_bytes;
 760
 761         if (t->burst_limited || asoc->max_burst == 0)
 762                 return;
 763
 764         max_burst_bytes = t->flight_size + (asoc->max_burst * asoc->pathmtu);
 765         if (max_burst_bytes < old_cwnd) {
 766                 t->cwnd = max_burst_bytes;
 767                 t->burst_limited = old_cwnd;
 768         }
 769 }
 770
 771 /* Restore the old cwnd congestion window, after the burst had it's
 772  * desired effect.
 773  */
 774 void sctp_transport_burst_reset(struct sctp_transport *t)
 775 {
 776         if (t->burst_limited) {
 777                 t->cwnd = t->burst_limited;
 778                 t->burst_limited = 0;
 779         }
 780 }
 781
 782 /* What is the next timeout value for this transport? */
 783 unsigned long sctp_transport_timeout(struct sctp_transport *trans)
 784 {
 785         /* RTO + timer slack +/- 50% of RTO */
 786         unsigned long timeout = trans->rto >> 1;
 787
 788         if (trans->state != SCTP_UNCONFIRMED &&
 789             trans->state != SCTP_PF)
 790                 timeout += trans->hbinterval;
 791
 792         return max_t(unsigned long, timeout, HZ / 5);
 793 }
 794
 795 /* Reset transport variables to their initial values */
 796 void sctp_transport_reset(struct sctp_transport *t)
 797 {
 798         struct sctp_association *asoc = t->asoc;
 799
 800         /* RFC 2960 (bis), Section 5.2.4
 801          * All the congestion control parameters (e.g., cwnd, ssthresh)
 802          * related to this peer MUST be reset to their initial values
 803          * (see Section 6.2.1)
 804          */
 805         t->cwnd = min(4*asoc->pathmtu, max_t(__u32, 2*asoc->pathmtu, 4380));
 806         t->burst_limited = 0;
 807         t->ssthresh = asoc->peer.i.a_rwnd;
 808         t->rto = asoc->rto_initial;
 809         sctp_max_rto(asoc, t);
 810         t->rtt = 0;
 811         t->srtt = 0;
 812         t->rttvar = 0;
 813
 814         /* Reset these additional variables so that we have a clean slate. */
 815         t->partial_bytes_acked = 0;
 816         t->flight_size = 0;
 817         t->error_count = 0;
 818         t->rto_pending = 0;
 819         t->hb_sent = 0;
 820
 821         /* Initialize the state information for SFR-CACC */
 822         t->cacc.changeover_active = 0;
 823         t->cacc.cycling_changeover = 0;
 824         t->cacc.next_tsn_at_change = 0;
 825         t->cacc.cacc_saw_newack = 0;
 826 }
 827
 828 /* Schedule retransmission on the given transport */
 829 void sctp_transport_immediate_rtx(struct sctp_transport *t)
 830 {
 831         /* Stop pending T3_rtx_timer */
 832         if (del_timer(&t->T3_rtx_timer))
 833                 sctp_transport_put(t);
 834
 835         sctp_retransmit(&t->asoc->outqueue, t, SCTP_RTXR_T3_RTX);
 836         if (!timer_pending(&t->T3_rtx_timer)) {
 837                 if (!mod_timer(&t->T3_rtx_timer, jiffies + t->rto))
 838                         sctp_transport_hold(t);
 839         }
 840 }
 841
 842 /* Drop dst */
 843 void sctp_transport_dst_release(struct sctp_transport *t)
 844 {
 845         dst_release(t->dst);
 846         t->dst = NULL;
 847         t->dst_pending_confirm = 0;
 848 }
 849
 850 /* Schedule neighbour confirm */
 851 void sctp_transport_dst_confirm(struct sctp_transport *t)
 852 {
 853         t->dst_pending_confirm = 1;
 854 }