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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-or-later
 /* SCTP kernel implementation
  * Copyright (c) 1999-2000 Cisco, Inc.
  * Copyright (c) 1999-2001 Motorola, Inc.
  * Copyright (c) 2001-2003 International Business Machines Corp.
  * Copyright (c) 2001 Intel Corp.
  * Copyright (c) 2001 La Monte H.P. Yarroll
  *
  * This file is part of the SCTP kernel implementation
  *
  * This module provides the abstraction for an SCTP transport representing
  * a remote transport address.  For local transport addresses, we just use
  * union sctp_addr.
  *
  * Please send any bug reports or fixes you make to the
  * email address(es):
  *    lksctp developers <linux-sctp@vger.kernel.org>
  *
  * Written or modified by:
  *    La Monte H.P. Yarroll <piggy@acm.org>
  *    Karl Knutson          <karl@athena.chicago.il.us>
  *    Jon Grimm             <jgrimm@us.ibm.com>
  *    Xingang Guo           <xingang.guo@intel.com>
  *    Hui Huang             <hui.huang@nokia.com>
  *    Sridhar Samudrala     <sri@us.ibm.com>
  *    Ardelle Fan       <ardelle.fan@intel.com>
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/random.h>
 #include <net/sctp/sctp.h>
 #include <net/sctp/sm.h>
 
 /* 1st Level Abstractions.  */
 
 /* Initialize a new transport from provided memory.  */
 static struct sctp_transport *sctp_transport_init(struct net *net,
                           struct sctp_transport *peer,
                           const union sctp_addr *addr,
                           gfp_t gfp)
 {
     /* Copy in the address.  */
     peer->af_specific = sctp_get_af_specific(addr->sa.sa_family);
     memcpy(&peer->ipaddr, addr, peer->af_specific->sockaddr_len);
     memset(&peer->saddr, 0, sizeof(union sctp_addr));
 
     peer->sack_generation = 0;
 
     /* From 6.3.1 RTO Calculation:
      *
      * C1) Until an RTT measurement has been made for a packet sent to the
      * given destination transport address, set RTO to the protocol
      * parameter 'RTO.Initial'.
      */
     peer->rto = msecs_to_jiffies(net->sctp.rto_initial);
 
     peer->last_time_heard = 0;
     peer->last_time_ecne_reduced = jiffies;
 
     peer->param_flags = SPP_HB_DISABLE |
                 SPP_PMTUD_ENABLE |
                 SPP_SACKDELAY_ENABLE;
 
     /* Initialize the default path max_retrans.  */
     peer->pathmaxrxt  = net->sctp.max_retrans_path;
     peer->pf_retrans  = net->sctp.pf_retrans;
 
     INIT_LIST_HEAD(&peer->transmitted);
     INIT_LIST_HEAD(&peer->send_ready);
     INIT_LIST_HEAD(&peer->transports);
 
     timer_setup(&peer->T3_rtx_timer, sctp_generate_t3_rtx_event, 0);
     timer_setup(&peer->hb_timer, sctp_generate_heartbeat_event, 0);
     timer_setup(&peer->reconf_timer, sctp_generate_reconf_event, 0);
     timer_setup(&peer->probe_timer, sctp_generate_probe_event, 0);
     timer_setup(&peer->proto_unreach_timer,
             sctp_generate_proto_unreach_event, 0);
 
     /* Initialize the 64-bit random nonce sent with heartbeat. */
     get_random_bytes(&peer->hb_nonce, sizeof(peer->hb_nonce));
 
     refcount_set(&peer->refcnt, 1);
 
     return peer;
 }
 
 /* Allocate and initialize a new transport.  */
 struct sctp_transport *sctp_transport_new(struct net *net,
                       const union sctp_addr *addr,
                       gfp_t gfp)
 {
     struct sctp_transport *transport;
 
     transport = kzalloc(sizeof(*transport), gfp);
     if (!transport)
         goto fail;
 
     if (!sctp_transport_init(net, transport, addr, gfp))
         goto fail_init;
 
     SCTP_DBG_OBJCNT_INC(transport);
 
     return transport;
 
 fail_init:
     kfree(transport);
 
 fail:
     return NULL;
 }
 
 /* This transport is no longer needed.  Free up if possible, or
  * delay until it last reference count.
  */
 void sctp_transport_free(struct sctp_transport *transport)
 {
     /* Try to delete the heartbeat timer.  */
     if (del_timer(&transport->hb_timer))
         sctp_transport_put(transport);
 
     /* Delete the T3_rtx timer if it's active.
      * There is no point in not doing this now and letting
      * structure hang around in memory since we know
      * the transport is going away.
      */
     if (del_timer(&transport->T3_rtx_timer))
         sctp_transport_put(transport);
 
     if (del_timer(&transport->reconf_timer))
         sctp_transport_put(transport);
 
     if (del_timer(&transport->probe_timer))
         sctp_transport_put(transport);
 
     /* Delete the ICMP proto unreachable timer if it's active. */
     if (del_timer(&transport->proto_unreach_timer))
         sctp_transport_put(transport);
 
     sctp_transport_put(transport);
 }
 
 static void sctp_transport_destroy_rcu(struct rcu_head *head)
 {
     struct sctp_transport *transport;
 
     transport = container_of(head, struct sctp_transport, rcu);
 
     dst_release(transport->dst);
     kfree(transport);
     SCTP_DBG_OBJCNT_DEC(transport);
 }
 
 /* Destroy the transport data structure.
  * Assumes there are no more users of this structure.
  */
 static void sctp_transport_destroy(struct sctp_transport *transport)
 {
     if (unlikely(refcount_read(&transport->refcnt))) {
         WARN(1, "Attempt to destroy undead transport %p!\n", transport);
         return;
     }
 
     sctp_packet_free(&transport->packet);
 
     if (transport->asoc)
         sctp_association_put(transport->asoc);
 
     call_rcu(&transport->rcu, sctp_transport_destroy_rcu);
 }
 
 /* Start T3_rtx timer if it is not already running and update the heartbeat
  * timer.  This routine is called every time a DATA chunk is sent.
  */
 void sctp_transport_reset_t3_rtx(struct sctp_transport *transport)
 {
     /* RFC 2960 6.3.2 Retransmission Timer Rules
      *
      * R1) Every time a DATA chunk is sent to any address(including a
      * retransmission), if the T3-rtx timer of that address is not running
      * start it running so that it will expire after the RTO of that
      * address.
      */
 
     if (!timer_pending(&transport->T3_rtx_timer))
         if (!mod_timer(&transport->T3_rtx_timer,
                    jiffies + transport->rto))
             sctp_transport_hold(transport);
 }
 
 void sctp_transport_reset_hb_timer(struct sctp_transport *transport)
 {
     unsigned long expires;
 
     /* When a data chunk is sent, reset the heartbeat interval.  */
     expires = jiffies + sctp_transport_timeout(transport);
     if ((time_before(transport->hb_timer.expires, expires) ||
          !timer_pending(&transport->hb_timer)) &&
         !mod_timer(&transport->hb_timer,
                expires + prandom_u32_max(transport->rto)))
         sctp_transport_hold(transport);
 }
 
 void sctp_transport_reset_reconf_timer(struct sctp_transport *transport)
 {
     if (!timer_pending(&transport->reconf_timer))
         if (!mod_timer(&transport->reconf_timer,
                    jiffies + transport->rto))
             sctp_transport_hold(transport);
 }
 
 void sctp_transport_reset_probe_timer(struct sctp_transport *transport)
 {
     if (!mod_timer(&transport->probe_timer,
                jiffies + transport->probe_interval))
         sctp_transport_hold(transport);
 }
 
 void sctp_transport_reset_raise_timer(struct sctp_transport *transport)
 {
     if (!mod_timer(&transport->probe_timer,
                jiffies + transport->probe_interval * 30))
         sctp_transport_hold(transport);
 }
 
 /* This transport has been assigned to an association.
  * Initialize fields from the association or from the sock itself.
  * Register the reference count in the association.
  */
 void sctp_transport_set_owner(struct sctp_transport *transport,
                   struct sctp_association *asoc)
 {
     transport->asoc = asoc;
     sctp_association_hold(asoc);
 }
 
 /* Initialize the pmtu of a transport. */
 void sctp_transport_pmtu(struct sctp_transport *transport, struct sock *sk)
 {
     /* If we don't have a fresh route, look one up */
     if (!transport->dst || transport->dst->obsolete) {
         sctp_transport_dst_release(transport);
         transport->af_specific->get_dst(transport, &transport->saddr,
                         &transport->fl, sk);
     }
 
     if (transport->param_flags & SPP_PMTUD_DISABLE) {
         struct sctp_association *asoc = transport->asoc;
 
         if (!transport->pathmtu && asoc && asoc->pathmtu)
             transport->pathmtu = asoc->pathmtu;
         if (transport->pathmtu)
             return;
     }
 
     if (transport->dst)
         transport->pathmtu = sctp_dst_mtu(transport->dst);
     else
         transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT;
 
     sctp_transport_pl_update(transport);
 }
 
 void sctp_transport_pl_send(struct sctp_transport *t)
 {
     if (t->pl.probe_count < SCTP_MAX_PROBES)
         goto out;
 
     t->pl.probe_count = 0;
     if (t->pl.state == SCTP_PL_BASE) {
         if (t->pl.probe_size == SCTP_BASE_PLPMTU) { /* BASE_PLPMTU Confirmation Failed */
             t->pl.state = SCTP_PL_ERROR; /* Base -> Error */
 
             t->pl.pmtu = SCTP_BASE_PLPMTU;
             t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
             sctp_assoc_sync_pmtu(t->asoc);
         }
     } else if (t->pl.state == SCTP_PL_SEARCH) {
         if (t->pl.pmtu == t->pl.probe_size) { /* Black Hole Detected */
             t->pl.state = SCTP_PL_BASE;  /* Search -> Base */
             t->pl.probe_size = SCTP_BASE_PLPMTU;
             t->pl.probe_high = 0;
 
             t->pl.pmtu = SCTP_BASE_PLPMTU;
             t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
             sctp_assoc_sync_pmtu(t->asoc);
         } else { /* Normal probe failure. */
             t->pl.probe_high = t->pl.probe_size;
             t->pl.probe_size = t->pl.pmtu;
         }
     } else if (t->pl.state == SCTP_PL_COMPLETE) {
         if (t->pl.pmtu == t->pl.probe_size) { /* Black Hole Detected */
             t->pl.state = SCTP_PL_BASE;  /* Search Complete -> Base */
             t->pl.probe_size = SCTP_BASE_PLPMTU;
 
             t->pl.pmtu = SCTP_BASE_PLPMTU;
             t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
             sctp_assoc_sync_pmtu(t->asoc);
         }
     }
 
 out:
     pr_debug("%s: PLPMTUD: transport: %p, state: %d, pmtu: %d, size: %d, high: %d\n",
          __func__, t, t->pl.state, t->pl.pmtu, t->pl.probe_size, t->pl.probe_high);
     t->pl.probe_count++;
 }
 
 bool sctp_transport_pl_recv(struct sctp_transport *t)
 {
     pr_debug("%s: PLPMTUD: transport: %p, state: %d, pmtu: %d, size: %d, high: %d\n",
          __func__, t, t->pl.state, t->pl.pmtu, t->pl.probe_size, t->pl.probe_high);
 
     t->pl.pmtu = t->pl.probe_size;
     t->pl.probe_count = 0;
     if (t->pl.state == SCTP_PL_BASE) {
         t->pl.state = SCTP_PL_SEARCH; /* Base -> Search */
         t->pl.probe_size += SCTP_PL_BIG_STEP;
     } else if (t->pl.state == SCTP_PL_ERROR) {
         t->pl.state = SCTP_PL_SEARCH; /* Error -> Search */
 
         t->pl.pmtu = t->pl.probe_size;
         t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
         sctp_assoc_sync_pmtu(t->asoc);
         t->pl.probe_size += SCTP_PL_BIG_STEP;
     } else if (t->pl.state == SCTP_PL_SEARCH) {
         if (!t->pl.probe_high) {
             t->pl.probe_size = min(t->pl.probe_size + SCTP_PL_BIG_STEP,
                            SCTP_MAX_PLPMTU);
             return false;
         }
         t->pl.probe_size += SCTP_PL_MIN_STEP;
         if (t->pl.probe_size >= t->pl.probe_high) {
             t->pl.probe_high = 0;
             t->pl.state = SCTP_PL_COMPLETE; /* Search -> Search Complete */
 
             t->pl.probe_size = t->pl.pmtu;
             t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
             sctp_assoc_sync_pmtu(t->asoc);
             sctp_transport_reset_raise_timer(t);
         }
     } else if (t->pl.state == SCTP_PL_COMPLETE) {
         /* Raise probe_size again after 30 * interval in Search Complete */
         t->pl.state = SCTP_PL_SEARCH; /* Search Complete -> Search */
         t->pl.probe_size += SCTP_PL_MIN_STEP;
     }
 
     return t->pl.state == SCTP_PL_COMPLETE;
 }
 
 static bool sctp_transport_pl_toobig(struct sctp_transport *t, u32 pmtu)
 {
     pr_debug("%s: PLPMTUD: transport: %p, state: %d, pmtu: %d, size: %d, ptb: %d\n",
          __func__, t, t->pl.state, t->pl.pmtu, t->pl.probe_size, pmtu);
 
     if (pmtu < SCTP_MIN_PLPMTU || pmtu >= t->pl.probe_size)
         return false;
 
     if (t->pl.state == SCTP_PL_BASE) {
         if (pmtu >= SCTP_MIN_PLPMTU && pmtu < SCTP_BASE_PLPMTU) {
             t->pl.state = SCTP_PL_ERROR; /* Base -> Error */
 
             t->pl.pmtu = SCTP_BASE_PLPMTU;
             t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
             return true;
         }
     } else if (t->pl.state == SCTP_PL_SEARCH) {
         if (pmtu >= SCTP_BASE_PLPMTU && pmtu < t->pl.pmtu) {
             t->pl.state = SCTP_PL_BASE;  /* Search -> Base */
             t->pl.probe_size = SCTP_BASE_PLPMTU;
             t->pl.probe_count = 0;
 
             t->pl.probe_high = 0;
             t->pl.pmtu = SCTP_BASE_PLPMTU;
             t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
             return true;
         } else if (pmtu > t->pl.pmtu && pmtu < t->pl.probe_size) {
             t->pl.probe_size = pmtu;
             t->pl.probe_count = 0;
         }
     } else if (t->pl.state == SCTP_PL_COMPLETE) {
         if (pmtu >= SCTP_BASE_PLPMTU && pmtu < t->pl.pmtu) {
             t->pl.state = SCTP_PL_BASE;  /* Complete -> Base */
             t->pl.probe_size = SCTP_BASE_PLPMTU;
             t->pl.probe_count = 0;
 
             t->pl.probe_high = 0;
             t->pl.pmtu = SCTP_BASE_PLPMTU;
             t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
             sctp_transport_reset_probe_timer(t);
             return true;
         }
     }
 
     return false;
 }
 
 bool sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu)
 {
     struct sock *sk = t->asoc->base.sk;
     struct dst_entry *dst;
     bool change = true;
 
     if (unlikely(pmtu < SCTP_DEFAULT_MINSEGMENT)) {
         pr_warn_ratelimited("%s: Reported pmtu %d too low, using default minimum of %d\n",
                     __func__, pmtu, SCTP_DEFAULT_MINSEGMENT);
         /* Use default minimum segment instead */
         pmtu = SCTP_DEFAULT_MINSEGMENT;
     }
     pmtu = SCTP_TRUNC4(pmtu);
 
     if (sctp_transport_pl_enabled(t))
         return sctp_transport_pl_toobig(t, pmtu - sctp_transport_pl_hlen(t));
 
     dst = sctp_transport_dst_check(t);
     if (dst) {
         struct sctp_pf *pf = sctp_get_pf_specific(dst->ops->family);
         union sctp_addr addr;
 
         pf->af->from_sk(&addr, sk);
         pf->to_sk_daddr(&t->ipaddr, sk);
         dst->ops->update_pmtu(dst, sk, NULL, pmtu, true);
         pf->to_sk_daddr(&addr, sk);
 
         dst = sctp_transport_dst_check(t);
     }
 
     if (!dst) {
         t->af_specific->get_dst(t, &t->saddr, &t->fl, sk);
         dst = t->dst;
     }
 
     if (dst) {
         /* Re-fetch, as under layers may have a higher minimum size */
         pmtu = sctp_dst_mtu(dst);
         change = t->pathmtu != pmtu;
     }
     t->pathmtu = pmtu;
 
     return change;
 }
 
 /* Caches the dst entry and source address for a transport's destination
  * address.
  */
 void sctp_transport_route(struct sctp_transport *transport,
               union sctp_addr *saddr, struct sctp_sock *opt)
 {
     struct sctp_association *asoc = transport->asoc;
     struct sctp_af *af = transport->af_specific;
 
     sctp_transport_dst_release(transport);
     af->get_dst(transport, saddr, &transport->fl, sctp_opt2sk(opt));
 
     if (saddr)
         memcpy(&transport->saddr, saddr, sizeof(union sctp_addr));
     else
         af->get_saddr(opt, transport, &transport->fl);
 
     sctp_transport_pmtu(transport, sctp_opt2sk(opt));
 
     /* Initialize sk->sk_rcv_saddr, if the transport is the
      * association's active path for getsockname().
      */
     if (transport->dst && asoc &&
         (!asoc->peer.primary_path || transport == asoc->peer.active_path))
         opt->pf->to_sk_saddr(&transport->saddr, asoc->base.sk);
 }
 
 /* Hold a reference to a transport.  */
 int sctp_transport_hold(struct sctp_transport *transport)
 {
     return refcount_inc_not_zero(&transport->refcnt);
 }
 
 /* Release a reference to a transport and clean up
  * if there are no more references.
  */
 void sctp_transport_put(struct sctp_transport *transport)
 {
     if (refcount_dec_and_test(&transport->refcnt))
         sctp_transport_destroy(transport);
 }
 
 /* Update transport's RTO based on the newly calculated RTT. */
 void sctp_transport_update_rto(struct sctp_transport *tp, __u32 rtt)
 {
     if (unlikely(!tp->rto_pending))
         /* We should not be doing any RTO updates unless rto_pending is set.  */
         pr_debug("%s: rto_pending not set on transport %p!\n", __func__, tp);
 
     if (tp->rttvar || tp->srtt) {
         struct net *net = tp->asoc->base.net;
         /* 6.3.1 C3) When a new RTT measurement R' is made, set
          * RTTVAR <- (1 - RTO.Beta) * RTTVAR + RTO.Beta * |SRTT - R'|
          * SRTT <- (1 - RTO.Alpha) * SRTT + RTO.Alpha * R'
          */
 
         /* Note:  The above algorithm has been rewritten to
          * express rto_beta and rto_alpha as inverse powers
          * of two.
          * For example, assuming the default value of RTO.Alpha of
          * 1/8, rto_alpha would be expressed as 3.
          */
         tp->rttvar = tp->rttvar - (tp->rttvar >> net->sctp.rto_beta)
             + (((__u32)abs((__s64)tp->srtt - (__s64)rtt)) >> net->sctp.rto_beta);
         tp->srtt = tp->srtt - (tp->srtt >> net->sctp.rto_alpha)
             + (rtt >> net->sctp.rto_alpha);
     } else {
         /* 6.3.1 C2) When the first RTT measurement R is made, set
          * SRTT <- R, RTTVAR <- R/2.
          */
         tp->srtt = rtt;
         tp->rttvar = rtt >> 1;
     }
 
     /* 6.3.1 G1) Whenever RTTVAR is computed, if RTTVAR = 0, then
      * adjust RTTVAR <- G, where G is the CLOCK GRANULARITY.
      */
     if (tp->rttvar == 0)
         tp->rttvar = SCTP_CLOCK_GRANULARITY;
 
     /* 6.3.1 C3) After the computation, update RTO <- SRTT + 4 * RTTVAR. */
     tp->rto = tp->srtt + (tp->rttvar << 2);
 
     /* 6.3.1 C6) Whenever RTO is computed, if it is less than RTO.Min
      * seconds then it is rounded up to RTO.Min seconds.
      */
     if (tp->rto < tp->asoc->rto_min)
         tp->rto = tp->asoc->rto_min;
 
     /* 6.3.1 C7) A maximum value may be placed on RTO provided it is
      * at least RTO.max seconds.
      */
     if (tp->rto > tp->asoc->rto_max)
         tp->rto = tp->asoc->rto_max;
 
     sctp_max_rto(tp->asoc, tp);
     tp->rtt = rtt;
 
     /* Reset rto_pending so that a new RTT measurement is started when a
      * new data chunk is sent.
      */
     tp->rto_pending = 0;
 
     pr_debug("%s: transport:%p, rtt:%d, srtt:%d rttvar:%d, rto:%ld\n",
          __func__, tp, rtt, tp->srtt, tp->rttvar, tp->rto);
 }
 
 /* This routine updates the transport's cwnd and partial_bytes_acked
  * parameters based on the bytes acked in the received SACK.
  */
 void sctp_transport_raise_cwnd(struct sctp_transport *transport,
                    __u32 sack_ctsn, __u32 bytes_acked)
 {
     struct sctp_association *asoc = transport->asoc;
     __u32 cwnd, ssthresh, flight_size, pba, pmtu;
 
     cwnd = transport->cwnd;
     flight_size = transport->flight_size;
 
     /* See if we need to exit Fast Recovery first */
     if (asoc->fast_recovery &&
         TSN_lte(asoc->fast_recovery_exit, sack_ctsn))
         asoc->fast_recovery = 0;
 
     ssthresh = transport->ssthresh;
     pba = transport->partial_bytes_acked;
     pmtu = transport->asoc->pathmtu;
 
     if (cwnd <= ssthresh) {
         /* RFC 4960 7.2.1
          * o  When cwnd is less than or equal to ssthresh, an SCTP
          *    endpoint MUST use the slow-start algorithm to increase
          *    cwnd only if the current congestion window is being fully
          *    utilized, an incoming SACK advances the Cumulative TSN
          *    Ack Point, and the data sender is not in Fast Recovery.
          *    Only when these three conditions are met can the cwnd be
          *    increased; otherwise, the cwnd MUST not be increased.
          *    If these conditions are met, then cwnd MUST be increased
          *    by, at most, the lesser of 1) the total size of the
          *    previously outstanding DATA chunk(s) acknowledged, and
          *    2) the destination's path MTU.  This upper bound protects
          *    against the ACK-Splitting attack outlined in [SAVAGE99].
          */
         if (asoc->fast_recovery)
             return;
 
         /* The appropriate cwnd increase algorithm is performed
          * if, and only if the congestion window is being fully
          * utilized.  Note that RFC4960 Errata 3.22 removed the
          * other condition on ctsn moving.
          */
         if (flight_size < cwnd)
             return;
 
         if (bytes_acked > pmtu)
             cwnd += pmtu;
         else
             cwnd += bytes_acked;
 
         pr_debug("%s: slow start: transport:%p, bytes_acked:%d, "
              "cwnd:%d, ssthresh:%d, flight_size:%d, pba:%d\n",
              __func__, transport, bytes_acked, cwnd, ssthresh,
              flight_size, pba);
     } else {
         /* RFC 2960 7.2.2 Whenever cwnd is greater than ssthresh,
          * upon each SACK arrival, increase partial_bytes_acked
          * by the total number of bytes of all new chunks
          * acknowledged in that SACK including chunks
          * acknowledged by the new Cumulative TSN Ack and by Gap
          * Ack Blocks. (updated by RFC4960 Errata 3.22)
          *
          * When partial_bytes_acked is greater than cwnd and
          * before the arrival of the SACK the sender had less
          * bytes of data outstanding than cwnd (i.e., before
          * arrival of the SACK, flightsize was less than cwnd),
          * reset partial_bytes_acked to cwnd. (RFC 4960 Errata
          * 3.26)
          *
          * When partial_bytes_acked is equal to or greater than
          * cwnd and before the arrival of the SACK the sender
          * had cwnd or more bytes of data outstanding (i.e.,
          * before arrival of the SACK, flightsize was greater
          * than or equal to cwnd), partial_bytes_acked is reset
          * to (partial_bytes_acked - cwnd). Next, cwnd is
          * increased by MTU. (RFC 4960 Errata 3.12)
          */
         pba += bytes_acked;
         if (pba > cwnd && flight_size < cwnd)
             pba = cwnd;
         if (pba >= cwnd && flight_size >= cwnd) {
             pba = pba - cwnd;
             cwnd += pmtu;
         }
 
         pr_debug("%s: congestion avoidance: transport:%p, "
              "bytes_acked:%d, cwnd:%d, ssthresh:%d, "
              "flight_size:%d, pba:%d\n", __func__,
              transport, bytes_acked, cwnd, ssthresh,
              flight_size, pba);
     }
 
     transport->cwnd = cwnd;
     transport->partial_bytes_acked = pba;
 }
 
 /* This routine is used to lower the transport's cwnd when congestion is
  * detected.
  */
 void sctp_transport_lower_cwnd(struct sctp_transport *transport,
                    enum sctp_lower_cwnd reason)
 {
     struct sctp_association *asoc = transport->asoc;
 
     switch (reason) {
     case SCTP_LOWER_CWND_T3_RTX:
         /* RFC 2960 Section 7.2.3, sctpimpguide
          * When the T3-rtx timer expires on an address, SCTP should
          * perform slow start by:
          *      ssthresh = max(cwnd/2, 4*MTU)
          *      cwnd = 1*MTU
          *      partial_bytes_acked = 0
          */
         transport->ssthresh = max(transport->cwnd/2,
                       4*asoc->pathmtu);
         transport->cwnd = asoc->pathmtu;
 
         /* T3-rtx also clears fast recovery */
         asoc->fast_recovery = 0;
         break;
 
     case SCTP_LOWER_CWND_FAST_RTX:
         /* RFC 2960 7.2.4 Adjust the ssthresh and cwnd of the
          * destination address(es) to which the missing DATA chunks
          * were last sent, according to the formula described in
          * Section 7.2.3.
          *
          * RFC 2960 7.2.3, sctpimpguide Upon detection of packet
          * losses from SACK (see Section 7.2.4), An endpoint
          * should do the following:
          *      ssthresh = max(cwnd/2, 4*MTU)
          *      cwnd = ssthresh
          *      partial_bytes_acked = 0
          */
         if (asoc->fast_recovery)
             return;
 
         /* Mark Fast recovery */
         asoc->fast_recovery = 1;
         asoc->fast_recovery_exit = asoc->next_tsn - 1;
 
         transport->ssthresh = max(transport->cwnd/2,
                       4*asoc->pathmtu);
         transport->cwnd = transport->ssthresh;
         break;
 
     case SCTP_LOWER_CWND_ECNE:
         /* RFC 2481 Section 6.1.2.
          * If the sender receives an ECN-Echo ACK packet
          * then the sender knows that congestion was encountered in the
          * network on the path from the sender to the receiver. The
          * indication of congestion should be treated just as a
          * congestion loss in non-ECN Capable TCP. That is, the TCP
          * source halves the congestion window "cwnd" and reduces the
          * slow start threshold "ssthresh".
          * A critical condition is that TCP does not react to
          * congestion indications more than once every window of
          * data (or more loosely more than once every round-trip time).
          */
         if (time_after(jiffies, transport->last_time_ecne_reduced +
                     transport->rtt)) {
             transport->ssthresh = max(transport->cwnd/2,
                           4*asoc->pathmtu);
             transport->cwnd = transport->ssthresh;
             transport->last_time_ecne_reduced = jiffies;
         }
         break;
 
     case SCTP_LOWER_CWND_INACTIVE:
         /* RFC 2960 Section 7.2.1, sctpimpguide
          * When the endpoint does not transmit data on a given
          * transport address, the cwnd of the transport address
          * should be adjusted to max(cwnd/2, 4*MTU) per RTO.
          * NOTE: Although the draft recommends that this check needs
          * to be done every RTO interval, we do it every hearbeat
          * interval.
          */
         transport->cwnd = max(transport->cwnd/2,
                      4*asoc->pathmtu);
         /* RFC 4960 Errata 3.27.2: also adjust sshthresh */
         transport->ssthresh = transport->cwnd;
         break;
     }
 
     transport->partial_bytes_acked = 0;
 
     pr_debug("%s: transport:%p, reason:%d, cwnd:%d, ssthresh:%d\n",
          __func__, transport, reason, transport->cwnd,
          transport->ssthresh);
 }
 
 /* Apply Max.Burst limit to the congestion window:
  * sctpimpguide-05 2.14.2
  * D) When the time comes for the sender to
  * transmit new DATA chunks, the protocol parameter Max.Burst MUST
  * first be applied to limit how many new DATA chunks may be sent.
  * The limit is applied by adjusting cwnd as follows:
  *  if ((flightsize+ Max.Burst * MTU) < cwnd)
  *      cwnd = flightsize + Max.Burst * MTU
  */
 
 void sctp_transport_burst_limited(struct sctp_transport *t)
 {
     struct sctp_association *asoc = t->asoc;
     u32 old_cwnd = t->cwnd;
     u32 max_burst_bytes;
 
     if (t->burst_limited || asoc->max_burst == 0)
         return;
 
     max_burst_bytes = t->flight_size + (asoc->max_burst * asoc->pathmtu);
     if (max_burst_bytes < old_cwnd) {
         t->cwnd = max_burst_bytes;
         t->burst_limited = old_cwnd;
     }
 }
 
 /* Restore the old cwnd congestion window, after the burst had it's
  * desired effect.
  */
 void sctp_transport_burst_reset(struct sctp_transport *t)
 {
     if (t->burst_limited) {
         t->cwnd = t->burst_limited;
         t->burst_limited = 0;
     }
 }
 
 /* What is the next timeout value for this transport? */
 unsigned long sctp_transport_timeout(struct sctp_transport *trans)
 {
     /* RTO + timer slack +/- 50% of RTO */
     unsigned long timeout = trans->rto >> 1;
 
     if (trans->state != SCTP_UNCONFIRMED &&
         trans->state != SCTP_PF)
         timeout += trans->hbinterval;
 
     return max_t(unsigned long, timeout, HZ / 5);
 }
 
 /* Reset transport variables to their initial values */
 void sctp_transport_reset(struct sctp_transport *t)
 {
     struct sctp_association *asoc = t->asoc;
 
     /* RFC 2960 (bis), Section 5.2.4
      * All the congestion control parameters (e.g., cwnd, ssthresh)
      * related to this peer MUST be reset to their initial values
      * (see Section 6.2.1)
      */
     t->cwnd = min(4*asoc->pathmtu, max_t(__u32, 2*asoc->pathmtu, 4380));
     t->burst_limited = 0;
     t->ssthresh = asoc->peer.i.a_rwnd;
     t->rto = asoc->rto_initial;
     sctp_max_rto(asoc, t);
     t->rtt = 0;
     t->srtt = 0;
     t->rttvar = 0;
 
     /* Reset these additional variables so that we have a clean slate. */
     t->partial_bytes_acked = 0;
     t->flight_size = 0;
     t->error_count = 0;
     t->rto_pending = 0;
     t->hb_sent = 0;
 
     /* Initialize the state information for SFR-CACC */
     t->cacc.changeover_active = 0;
     t->cacc.cycling_changeover = 0;
     t->cacc.next_tsn_at_change = 0;
     t->cacc.cacc_saw_newack = 0;
 }
 
 /* Schedule retransmission on the given transport */
 void sctp_transport_immediate_rtx(struct sctp_transport *t)
 {
     /* Stop pending T3_rtx_timer */
     if (del_timer(&t->T3_rtx_timer))
         sctp_transport_put(t);
 
     sctp_retransmit(&t->asoc->outqueue, t, SCTP_RTXR_T3_RTX);
     if (!timer_pending(&t->T3_rtx_timer)) {
         if (!mod_timer(&t->T3_rtx_timer, jiffies + t->rto))
             sctp_transport_hold(t);
     }
 }
 
 /* Drop dst */
 void sctp_transport_dst_release(struct sctp_transport *t)
 {
     dst_release(t->dst);
     t->dst = NULL;
     t->dst_pending_confirm = 0;
 }
 
 /* Schedule neighbour confirm */
 void sctp_transport_dst_confirm(struct sctp_transport *t)
 {
     t->dst_pending_confirm = 1;
 }

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