// 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 void 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);
}

/* 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_obj(*transport, gfp);
        if (!transport)
                return NULL;

        sctp_transport_init(net, transport, addr, gfp);

        SCTP_DBG_OBJCNT_INC(transport);

        return transport;
}

/* 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)
{
        transport->dead = 1;

        /* Try to delete the heartbeat timer.  */
        if (timer_delete(&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 (timer_delete(&transport->T3_rtx_timer))
                sctp_transport_put(transport);

        if (timer_delete(&transport->reconf_timer))
                sctp_transport_put(transport);

        if (timer_delete(&transport->probe_timer))
                sctp_transport_put(transport);

        /* Delete the ICMP proto unreachable timer if it's active. */
        if (timer_delete(&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 (!mod_timer(&transport->hb_timer,
                       expires + get_random_u32_below(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 || READ_ONCE(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) {
                        if (t->pl.probe_size < SCTP_MAX_PLPMTU) {
                                t->pl.probe_size = min(t->pl.probe_size + SCTP_PL_BIG_STEP,
                                                       SCTP_MAX_PLPMTU);
                                return false;
                        }
                        t->pl.probe_high = SCTP_MAX_PLPMTU;
                }
                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 = min(t->pl.probe_size + SCTP_PL_MIN_STEP, SCTP_MAX_PLPMTU);
        }

        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;
                unsigned int rto_beta, rto_alpha;
                /* 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.
                 */
                rto_beta = READ_ONCE(net->sctp.rto_beta);
                if (rto_beta < 32)
                        tp->rttvar = tp->rttvar - (tp->rttvar >> rto_beta)
                                + (((__u32)abs((__s64)tp->srtt - (__s64)rtt)) >> rto_beta);
                rto_alpha = READ_ONCE(net->sctp.rto_alpha);
                if (rto_alpha < 32)
                        tp->srtt = tp->srtt - (tp->srtt >> rto_alpha)
                                + (rtt >> 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 (timer_delete(&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;
}