transport.c

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/* 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 tranport representing
 * a remote transport address.  For local transport addresses, we just use
 * union sctp_addr.
 *
 * This SCTP implementation is free software;
 * you can redistribute it and/or modify it under the terms of
 * the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This SCTP implementation is distributed in the hope that it
 * will be useful, but WITHOUT ANY WARRANTY; without even the implied
 *                 ************************
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with GNU CC; see the file COPYING.  If not, write to
 * the Free Software Foundation, 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * Please send any bug reports or fixes you make to the
 * email address(es):
 *    lksctp developers <[email protected]>
 *
 * Or submit a bug report through the following website:
 *    http://www.sf.net/projects/lksctp
 *
 * Written or modified by:
 *    La Monte H.P. Yarroll <[email protected]>
 *    Karl Knutson          <[email protected]>
 *    Jon Grimm             <[email protected]>
 *    Xingang Guo           <[email protected]>
 *    Hui Huang             <[email protected]>
 *    Sridhar Samudrala     <[email protected]>
 *    Ardelle Fan       <[email protected]>
 *
 * Any bugs reported given to us we will try to fix... any fixes shared will
 * be incorporated into the next SCTP release.
 */

#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->ipaddr = *addr;
    peer->af_specific = sctp_get_af_specific(addr->sa.sa_family);
    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 = jiffies;
    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);

    setup_timer(&peer->T3_rtx_timer, sctp_generate_t3_rtx_event,
            (unsigned long)peer);
    setup_timer(&peer->hb_timer, sctp_generate_heartbeat_event,
            (unsigned long)peer);
    setup_timer(&peer->proto_unreach_timer,
            sctp_generate_proto_unreach_event, (unsigned long)peer);

    /* Initialize the 64-bit random nonce sent with heartbeat. */
    get_random_bytes(&peer->hb_nonce, sizeof(peer->hb_nonce));

    atomic_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 = t_new(struct sctp_transport, gfp);
    if (!transport)
        goto fail;

    if (!sctp_transport_init(net, transport, addr, gfp))
        goto fail_init;

    transport->malloced = 1;
    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)
{
    transport->dead = 1;

    /* 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 tranport is going away.
     */
    if (timer_pending(&transport->T3_rtx_timer) &&
        del_timer(&transport->T3_rtx_timer))
        sctp_transport_put(transport);

    /* Delete the ICMP proto unreachable timer if it's active. */
    if (timer_pending(&transport->proto_unreach_timer) &&
        del_timer(&transport->proto_unreach_timer))
        sctp_association_put(transport->asoc);

    sctp_transport_put(transport);
}

/* Destroy the transport data structure.
 * Assumes there are no more users of this structure.
 */
static void sctp_transport_destroy(struct sctp_transport *transport)
{
    SCTP_ASSERT(transport->dead, "Transport is not dead", return);

    if (transport->asoc)
        sctp_association_put(transport->asoc);

    sctp_packet_free(&transport->packet);

    dst_release(transport->dst);
    kfree(transport);
    SCTP_DBG_OBJCNT_DEC(transport);
}

/* 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_timers(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);

    /* When a data chunk is sent, reset the heartbeat interval.  */
    if (!mod_timer(&transport->hb_timer,
               sctp_transport_timeout(transport)))
        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) {
        dst_release(transport->dst);
        transport->af_specific->get_dst(transport, &transport->saddr,
                        &transport->fl, sk);
    }

    if (transport->dst) {
        transport->pathmtu = dst_mtu(transport->dst);
    } else
        transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT;
}

void sctp_transport_update_pmtu(struct sock *sk, struct sctp_transport *t, u32 pmtu)
{
    struct dst_entry *dst;

    if (unlikely(pmtu < SCTP_DEFAULT_MINSEGMENT)) {
        pr_warn("%s: Reported pmtu %d too low, using default minimum of %d\n",
            __func__, pmtu,
            SCTP_DEFAULT_MINSEGMENT);
        /* Use default minimum segment size and disable
         * pmtu discovery on this transport.
         */
        t->pathmtu = SCTP_DEFAULT_MINSEGMENT;
    } else {
        t->pathmtu = pmtu;
    }

    dst = sctp_transport_dst_check(t);
    if (!dst)
        t->af_specific->get_dst(t, &t->saddr, &t->fl, sk);

    if (dst) {
        dst->ops->update_pmtu(dst, sk, NULL, pmtu);

        dst = sctp_transport_dst_check(t);
        if (!dst)
            t->af_specific->get_dst(t, &t->saddr, &t->fl, sk);
    }
}

/* 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;

    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);

    if ((transport->param_flags & SPP_PMTUD_DISABLE) && transport->pathmtu) {
        return;
    }
    if (transport->dst) {
        transport->pathmtu = dst_mtu(transport->dst);

        /* Initialize sk->sk_rcv_saddr, if the transport is the
         * association's active path for getsockname().
         */
        if (asoc && (!asoc->peer.primary_path ||
                (transport == asoc->peer.active_path)))
            opt->pf->af->to_sk_saddr(&transport->saddr,
                         asoc->base.sk);
    } else
        transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT;
}

/* Hold a reference to a transport.  */
void sctp_transport_hold(struct sctp_transport *transport)
{
    atomic_inc(&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 (atomic_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)
{
    /* Check for valid transport.  */
    SCTP_ASSERT(tp, "NULL transport", return);

    /* We should not be doing any RTO updates unless rto_pending is set.  */
    SCTP_ASSERT(tp->rto_pending, "rto_pending not set", return);

    if (tp->rttvar || tp->srtt) {
        struct net *net = sock_net(tp->asoc->base.sk);
        /* 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)abs64((__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;

    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;

    SCTP_DEBUG_PRINTK("%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;

    /* The appropriate cwnd increase algorithm is performed if, and only
     * if the cumulative TSN whould advanced and the congestion window is
     * being fully utilized.
     */
    if (TSN_lte(sack_ctsn, transport->asoc->ctsn_ack_point) ||
        (flight_size < cwnd))
        return;

    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;

        if (bytes_acked > pmtu)
            cwnd += pmtu;
        else
            cwnd += bytes_acked;
        SCTP_DEBUG_PRINTK("%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 that advances the Cumulative TSN Ack
         * Point, 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.
         *
         * 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),
         * increase cwnd by MTU, and reset partial_bytes_acked to
         * (partial_bytes_acked - cwnd).
         */
        pba += bytes_acked;
        if (pba >= cwnd) {
            cwnd += pmtu;
            pba = ((cwnd < pba) ? (pba - cwnd) : 0);
        }
        SCTP_DEBUG_PRINTK("%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,
                   sctp_lower_cwnd_t 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);
        break;
    }

    transport->partial_bytes_acked = 0;
    SCTP_DEBUG_PRINTK("%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)
        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 *t)
{
    unsigned long timeout;
    timeout = t->rto + sctp_jitter(t->rto);
    if ((t->state != SCTP_UNCONFIRMED) &&
        (t->state != SCTP_PF))
        timeout += t->hbinterval;
    timeout += jiffies;
    return timeout;
}

/* 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;
    t->rtt = 0;
    t->srtt = 0;
    t->rttvar = 0;

    /* Reset these additional varibles 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_pending(&t->T3_rtx_timer)) {
        (void)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);
    }
    return;
}