Documentation/networking: more accurate LCO explanation

[linux/fpc-iii.git] / net / sctp / associola.c

/* SCTP kernel implementation
 * (C) Copyright IBM Corp. 2001, 2004
 * Copyright (c) 1999-2000 Cisco, Inc.
 * Copyright (c) 1999-2001 Motorola, Inc.
 * 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 association.
 *
 * 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, see
 * <http://www.gnu.org/licenses/>.
 *
 * 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>
 *    Daisy Chang           <daisyc@us.ibm.com>
 *    Ryan Layer            <rmlayer@us.ibm.com>
 *    Kevin Gao             <kevin.gao@intel.com>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/poll.h>
#include <linux/init.h>

#include <linux/slab.h>
#include <linux/in.h>
#include <net/ipv6.h>
#include <net/sctp/sctp.h>
#include <net/sctp/sm.h>

/* Forward declarations for internal functions. */
static void sctp_select_active_and_retran_path(struct sctp_association *asoc);
static void sctp_assoc_bh_rcv(struct work_struct *work);
static void sctp_assoc_free_asconf_acks(struct sctp_association *asoc);
static void sctp_assoc_free_asconf_queue(struct sctp_association *asoc);

/* 1st Level Abstractions. */

/* Initialize a new association from provided memory. */
static struct sctp_association *sctp_association_init(struct sctp_association *asoc,
                                          const struct sctp_endpoint *ep,
                                          const struct sock *sk,
                                          sctp_scope_t scope,
                                          gfp_t gfp)
{
        struct net *net = sock_net(sk);
        struct sctp_sock *sp;
        int i;
        sctp_paramhdr_t *p;
        int err;

        /* Retrieve the SCTP per socket area.  */
        sp = sctp_sk((struct sock *)sk);

        /* Discarding const is appropriate here.  */
        asoc->ep = (struct sctp_endpoint *)ep;
        asoc->base.sk = (struct sock *)sk;

        sctp_endpoint_hold(asoc->ep);
        sock_hold(asoc->base.sk);

        /* Initialize the common base substructure.  */
        asoc->base.type = SCTP_EP_TYPE_ASSOCIATION;

        /* Initialize the object handling fields.  */
        atomic_set(&asoc->base.refcnt, 1);

        /* Initialize the bind addr area.  */
        sctp_bind_addr_init(&asoc->base.bind_addr, ep->base.bind_addr.port);

        asoc->state = SCTP_STATE_CLOSED;
        asoc->cookie_life = ms_to_ktime(sp->assocparams.sasoc_cookie_life);
        asoc->user_frag = sp->user_frag;

        /* Set the association max_retrans and RTO values from the
         * socket values.
         */
        asoc->max_retrans = sp->assocparams.sasoc_asocmaxrxt;
        asoc->pf_retrans  = net->sctp.pf_retrans;

        asoc->rto_initial = msecs_to_jiffies(sp->rtoinfo.srto_initial);
        asoc->rto_max = msecs_to_jiffies(sp->rtoinfo.srto_max);
        asoc->rto_min = msecs_to_jiffies(sp->rtoinfo.srto_min);

        /* Initialize the association's heartbeat interval based on the
         * sock configured value.
         */
        asoc->hbinterval = msecs_to_jiffies(sp->hbinterval);

        /* Initialize path max retrans value. */
        asoc->pathmaxrxt = sp->pathmaxrxt;

        /* Initialize default path MTU. */
        asoc->pathmtu = sp->pathmtu;

        /* Set association default SACK delay */
        asoc->sackdelay = msecs_to_jiffies(sp->sackdelay);
        asoc->sackfreq = sp->sackfreq;

        /* Set the association default flags controlling
         * Heartbeat, SACK delay, and Path MTU Discovery.
         */
        asoc->param_flags = sp->param_flags;

        /* Initialize the maximum number of new data packets that can be sent
         * in a burst.
         */
        asoc->max_burst = sp->max_burst;

        /* initialize association timers */
        asoc->timeouts[SCTP_EVENT_TIMEOUT_T1_COOKIE] = asoc->rto_initial;
        asoc->timeouts[SCTP_EVENT_TIMEOUT_T1_INIT] = asoc->rto_initial;
        asoc->timeouts[SCTP_EVENT_TIMEOUT_T2_SHUTDOWN] = asoc->rto_initial;

        /* sctpimpguide Section 2.12.2
         * If the 'T5-shutdown-guard' timer is used, it SHOULD be set to the
         * recommended value of 5 times 'RTO.Max'.
         */
        asoc->timeouts[SCTP_EVENT_TIMEOUT_T5_SHUTDOWN_GUARD]
                = 5 * asoc->rto_max;

        asoc->timeouts[SCTP_EVENT_TIMEOUT_SACK] = asoc->sackdelay;
        asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE] = sp->autoclose * HZ;

        /* Initializes the timers */
        for (i = SCTP_EVENT_TIMEOUT_NONE; i < SCTP_NUM_TIMEOUT_TYPES; ++i)
                setup_timer(&asoc->timers[i], sctp_timer_events[i],
                                (unsigned long)asoc);

        /* Pull default initialization values from the sock options.
         * Note: This assumes that the values have already been
         * validated in the sock.
         */
        asoc->c.sinit_max_instreams = sp->initmsg.sinit_max_instreams;
        asoc->c.sinit_num_ostreams  = sp->initmsg.sinit_num_ostreams;
        asoc->max_init_attempts = sp->initmsg.sinit_max_attempts;

        asoc->max_init_timeo =
                 msecs_to_jiffies(sp->initmsg.sinit_max_init_timeo);

        /* Set the local window size for receive.
         * This is also the rcvbuf space per association.
         * RFC 6 - A SCTP receiver MUST be able to receive a minimum of
         * 1500 bytes in one SCTP packet.
         */
        if ((sk->sk_rcvbuf/2) < SCTP_DEFAULT_MINWINDOW)
                asoc->rwnd = SCTP_DEFAULT_MINWINDOW;
        else
                asoc->rwnd = sk->sk_rcvbuf/2;

        asoc->a_rwnd = asoc->rwnd;

        /* Use my own max window until I learn something better.  */
        asoc->peer.rwnd = SCTP_DEFAULT_MAXWINDOW;

        /* Initialize the receive memory counter */
        atomic_set(&asoc->rmem_alloc, 0);

        init_waitqueue_head(&asoc->wait);

        asoc->c.my_vtag = sctp_generate_tag(ep);
        asoc->c.my_port = ep->base.bind_addr.port;

        asoc->c.initial_tsn = sctp_generate_tsn(ep);

        asoc->next_tsn = asoc->c.initial_tsn;

        asoc->ctsn_ack_point = asoc->next_tsn - 1;
        asoc->adv_peer_ack_point = asoc->ctsn_ack_point;
        asoc->highest_sacked = asoc->ctsn_ack_point;
        asoc->last_cwr_tsn = asoc->ctsn_ack_point;

        /* ADDIP Section 4.1 Asconf Chunk Procedures
         *
         * When an endpoint has an ASCONF signaled change to be sent to the
         * remote endpoint it should do the following:
         * ...
         * A2) a serial number should be assigned to the chunk. The serial
         * number SHOULD be a monotonically increasing number. The serial
         * numbers SHOULD be initialized at the start of the
         * association to the same value as the initial TSN.
         */
        asoc->addip_serial = asoc->c.initial_tsn;

        INIT_LIST_HEAD(&asoc->addip_chunk_list);
        INIT_LIST_HEAD(&asoc->asconf_ack_list);

        /* Make an empty list of remote transport addresses.  */
        INIT_LIST_HEAD(&asoc->peer.transport_addr_list);

        /* RFC 2960 5.1 Normal Establishment of an Association
         *
         * After the reception of the first data chunk in an
         * association the endpoint must immediately respond with a
         * sack to acknowledge the data chunk.  Subsequent
         * acknowledgements should be done as described in Section
         * 6.2.
         *
         * [We implement this by telling a new association that it
         * already received one packet.]
         */
        asoc->peer.sack_needed = 1;
        asoc->peer.sack_generation = 1;

        /* Assume that the peer will tell us if he recognizes ASCONF
         * as part of INIT exchange.
         * The sctp_addip_noauth option is there for backward compatibility
         * and will revert old behavior.
         */
        if (net->sctp.addip_noauth)
                asoc->peer.asconf_capable = 1;

        /* Create an input queue.  */
        sctp_inq_init(&asoc->base.inqueue);
        sctp_inq_set_th_handler(&asoc->base.inqueue, sctp_assoc_bh_rcv);

        /* Create an output queue.  */
        sctp_outq_init(asoc, &asoc->outqueue);

        if (!sctp_ulpq_init(&asoc->ulpq, asoc))
                goto fail_init;

        /* Assume that peer would support both address types unless we are
         * told otherwise.
         */
        asoc->peer.ipv4_address = 1;
        if (asoc->base.sk->sk_family == PF_INET6)
                asoc->peer.ipv6_address = 1;
        INIT_LIST_HEAD(&asoc->asocs);

        asoc->default_stream = sp->default_stream;
        asoc->default_ppid = sp->default_ppid;
        asoc->default_flags = sp->default_flags;
        asoc->default_context = sp->default_context;
        asoc->default_timetolive = sp->default_timetolive;
        asoc->default_rcv_context = sp->default_rcv_context;

        /* AUTH related initializations */
        INIT_LIST_HEAD(&asoc->endpoint_shared_keys);
        err = sctp_auth_asoc_copy_shkeys(ep, asoc, gfp);
        if (err)
                goto fail_init;

        asoc->active_key_id = ep->active_key_id;

        /* Save the hmacs and chunks list into this association */
        if (ep->auth_hmacs_list)
                memcpy(asoc->c.auth_hmacs, ep->auth_hmacs_list,
                        ntohs(ep->auth_hmacs_list->param_hdr.length));
        if (ep->auth_chunk_list)
                memcpy(asoc->c.auth_chunks, ep->auth_chunk_list,
                        ntohs(ep->auth_chunk_list->param_hdr.length));

        /* Get the AUTH random number for this association */
        p = (sctp_paramhdr_t *)asoc->c.auth_random;
        p->type = SCTP_PARAM_RANDOM;
        p->length = htons(sizeof(sctp_paramhdr_t) + SCTP_AUTH_RANDOM_LENGTH);
        get_random_bytes(p+1, SCTP_AUTH_RANDOM_LENGTH);

        return asoc;

fail_init:
        sock_put(asoc->base.sk);
        sctp_endpoint_put(asoc->ep);
        return NULL;
}

/* Allocate and initialize a new association */
struct sctp_association *sctp_association_new(const struct sctp_endpoint *ep,
                                         const struct sock *sk,
                                         sctp_scope_t scope,
                                         gfp_t gfp)
{
        struct sctp_association *asoc;

        asoc = kzalloc(sizeof(*asoc), gfp);
        if (!asoc)
                goto fail;

        if (!sctp_association_init(asoc, ep, sk, scope, gfp))
                goto fail_init;

        SCTP_DBG_OBJCNT_INC(assoc);

        pr_debug("Created asoc %p\n", asoc);

        return asoc;

fail_init:
        kfree(asoc);
fail:
        return NULL;
}

/* Free this association if possible.  There may still be users, so
 * the actual deallocation may be delayed.
 */
void sctp_association_free(struct sctp_association *asoc)
{
        struct sock *sk = asoc->base.sk;
        struct sctp_transport *transport;
        struct list_head *pos, *temp;
        int i;

        /* Only real associations count against the endpoint, so
         * don't bother for if this is a temporary association.
         */
        if (!list_empty(&asoc->asocs)) {
                list_del(&asoc->asocs);

                /* Decrement the backlog value for a TCP-style listening
                 * socket.
                 */
                if (sctp_style(sk, TCP) && sctp_sstate(sk, LISTENING))
                        sk->sk_ack_backlog--;
        }

        /* Mark as dead, so other users can know this structure is
         * going away.
         */
        asoc->base.dead = true;

        /* Dispose of any data lying around in the outqueue. */
        sctp_outq_free(&asoc->outqueue);

        /* Dispose of any pending messages for the upper layer. */
        sctp_ulpq_free(&asoc->ulpq);

        /* Dispose of any pending chunks on the inqueue. */
        sctp_inq_free(&asoc->base.inqueue);

        sctp_tsnmap_free(&asoc->peer.tsn_map);

        /* Free ssnmap storage. */
        sctp_ssnmap_free(asoc->ssnmap);

        /* Clean up the bound address list. */
        sctp_bind_addr_free(&asoc->base.bind_addr);

        /* Do we need to go through all of our timers and
         * delete them?   To be safe we will try to delete all, but we
         * should be able to go through and make a guess based
         * on our state.
         */
        for (i = SCTP_EVENT_TIMEOUT_NONE; i < SCTP_NUM_TIMEOUT_TYPES; ++i) {
                if (del_timer(&asoc->timers[i]))
                        sctp_association_put(asoc);
        }

        /* Free peer's cached cookie. */
        kfree(asoc->peer.cookie);
        kfree(asoc->peer.peer_random);
        kfree(asoc->peer.peer_chunks);
        kfree(asoc->peer.peer_hmacs);

        /* Release the transport structures. */
        list_for_each_safe(pos, temp, &asoc->peer.transport_addr_list) {
                transport = list_entry(pos, struct sctp_transport, transports);
                list_del_rcu(pos);
                sctp_unhash_transport(transport);
                sctp_transport_free(transport);
        }

        asoc->peer.transport_count = 0;

        sctp_asconf_queue_teardown(asoc);

        /* Free pending address space being deleted */
        kfree(asoc->asconf_addr_del_pending);

        /* AUTH - Free the endpoint shared keys */
        sctp_auth_destroy_keys(&asoc->endpoint_shared_keys);

        /* AUTH - Free the association shared key */
        sctp_auth_key_put(asoc->asoc_shared_key);

        sctp_association_put(asoc);
}

/* Cleanup and free up an association. */
static void sctp_association_destroy(struct sctp_association *asoc)
{
        if (unlikely(!asoc->base.dead)) {
                WARN(1, "Attempt to destroy undead association %p!\n", asoc);
                return;
        }

        sctp_endpoint_put(asoc->ep);
        sock_put(asoc->base.sk);

        if (asoc->assoc_id != 0) {
                spin_lock_bh(&sctp_assocs_id_lock);
                idr_remove(&sctp_assocs_id, asoc->assoc_id);
                spin_unlock_bh(&sctp_assocs_id_lock);
        }

        WARN_ON(atomic_read(&asoc->rmem_alloc));

        kfree(asoc);
        SCTP_DBG_OBJCNT_DEC(assoc);
}

/* Change the primary destination address for the peer. */
void sctp_assoc_set_primary(struct sctp_association *asoc,
                            struct sctp_transport *transport)
{
        int changeover = 0;

        /* it's a changeover only if we already have a primary path
         * that we are changing
         */
        if (asoc->peer.primary_path != NULL &&
            asoc->peer.primary_path != transport)
                changeover = 1 ;

        asoc->peer.primary_path = transport;

        /* Set a default msg_name for events. */
        memcpy(&asoc->peer.primary_addr, &transport->ipaddr,
               sizeof(union sctp_addr));

        /* If the primary path is changing, assume that the
         * user wants to use this new path.
         */
        if ((transport->state == SCTP_ACTIVE) ||
            (transport->state == SCTP_UNKNOWN))
                asoc->peer.active_path = transport;

        /*
         * SFR-CACC algorithm:
         * Upon the receipt of a request to change the primary
         * destination address, on the data structure for the new
         * primary destination, the sender MUST do the following:
         *
         * 1) If CHANGEOVER_ACTIVE is set, then there was a switch
         * to this destination address earlier. The sender MUST set
         * CYCLING_CHANGEOVER to indicate that this switch is a
         * double switch to the same destination address.
         *
         * Really, only bother is we have data queued or outstanding on
         * the association.
         */
        if (!asoc->outqueue.outstanding_bytes && !asoc->outqueue.out_qlen)
                return;

        if (transport->cacc.changeover_active)
                transport->cacc.cycling_changeover = changeover;

        /* 2) The sender MUST set CHANGEOVER_ACTIVE to indicate that
         * a changeover has occurred.
         */
        transport->cacc.changeover_active = changeover;

        /* 3) The sender MUST store the next TSN to be sent in
         * next_tsn_at_change.
         */
        transport->cacc.next_tsn_at_change = asoc->next_tsn;
}

/* Remove a transport from an association.  */
void sctp_assoc_rm_peer(struct sctp_association *asoc,
                        struct sctp_transport *peer)
{
        struct list_head        *pos;
        struct sctp_transport   *transport;

        pr_debug("%s: association:%p addr:%pISpc\n",
                 __func__, asoc, &peer->ipaddr.sa);

        /* If we are to remove the current retran_path, update it
         * to the next peer before removing this peer from the list.
         */
        if (asoc->peer.retran_path == peer)
                sctp_assoc_update_retran_path(asoc);

        /* Remove this peer from the list. */
        list_del_rcu(&peer->transports);
        /* Remove this peer from the transport hashtable */
        sctp_unhash_transport(peer);

        /* Get the first transport of asoc. */
        pos = asoc->peer.transport_addr_list.next;
        transport = list_entry(pos, struct sctp_transport, transports);

        /* Update any entries that match the peer to be deleted. */
        if (asoc->peer.primary_path == peer)
                sctp_assoc_set_primary(asoc, transport);
        if (asoc->peer.active_path == peer)
                asoc->peer.active_path = transport;
        if (asoc->peer.retran_path == peer)
                asoc->peer.retran_path = transport;
        if (asoc->peer.last_data_from == peer)
                asoc->peer.last_data_from = transport;

        /* If we remove the transport an INIT was last sent to, set it to
         * NULL. Combined with the update of the retran path above, this
         * will cause the next INIT to be sent to the next available
         * transport, maintaining the cycle.
         */
        if (asoc->init_last_sent_to == peer)
                asoc->init_last_sent_to = NULL;

        /* If we remove the transport an SHUTDOWN was last sent to, set it
         * to NULL. Combined with the update of the retran path above, this
         * will cause the next SHUTDOWN to be sent to the next available
         * transport, maintaining the cycle.
         */
        if (asoc->shutdown_last_sent_to == peer)
                asoc->shutdown_last_sent_to = NULL;

        /* If we remove the transport an ASCONF was last sent to, set it to
         * NULL.
         */
        if (asoc->addip_last_asconf &&
            asoc->addip_last_asconf->transport == peer)
                asoc->addip_last_asconf->transport = NULL;

        /* If we have something on the transmitted list, we have to
         * save it off.  The best place is the active path.
         */
        if (!list_empty(&peer->transmitted)) {
                struct sctp_transport *active = asoc->peer.active_path;
                struct sctp_chunk *ch;

                /* Reset the transport of each chunk on this list */
                list_for_each_entry(ch, &peer->transmitted,
                                        transmitted_list) {
                        ch->transport = NULL;
                        ch->rtt_in_progress = 0;
                }

                list_splice_tail_init(&peer->transmitted,
                                        &active->transmitted);

                /* Start a T3 timer here in case it wasn't running so
                 * that these migrated packets have a chance to get
                 * retransmitted.
                 */
                if (!timer_pending(&active->T3_rtx_timer))
                        if (!mod_timer(&active->T3_rtx_timer,
                                        jiffies + active->rto))
                                sctp_transport_hold(active);
        }

        asoc->peer.transport_count--;

        sctp_transport_free(peer);
}

/* Add a transport address to an association.  */
struct sctp_transport *sctp_assoc_add_peer(struct sctp_association *asoc,
                                           const union sctp_addr *addr,
                                           const gfp_t gfp,
                                           const int peer_state)
{
        struct net *net = sock_net(asoc->base.sk);
        struct sctp_transport *peer;
        struct sctp_sock *sp;
        unsigned short port;

        sp = sctp_sk(asoc->base.sk);

        /* AF_INET and AF_INET6 share common port field. */
        port = ntohs(addr->v4.sin_port);

        pr_debug("%s: association:%p addr:%pISpc state:%d\n", __func__,
                 asoc, &addr->sa, peer_state);

        /* Set the port if it has not been set yet.  */
        if (0 == asoc->peer.port)
                asoc->peer.port = port;

        /* Check to see if this is a duplicate. */
        peer = sctp_assoc_lookup_paddr(asoc, addr);
        if (peer) {
                /* An UNKNOWN state is only set on transports added by
                 * user in sctp_connectx() call.  Such transports should be
                 * considered CONFIRMED per RFC 4960, Section 5.4.
                 */
                if (peer->state == SCTP_UNKNOWN) {
                        peer->state = SCTP_ACTIVE;
                }
                return peer;
        }

        peer = sctp_transport_new(net, addr, gfp);
        if (!peer)
                return NULL;

        sctp_transport_set_owner(peer, asoc);

        /* Initialize the peer's heartbeat interval based on the
         * association configured value.
         */
        peer->hbinterval = asoc->hbinterval;

        /* Set the path max_retrans.  */
        peer->pathmaxrxt = asoc->pathmaxrxt;

        /* And the partial failure retrans threshold */
        peer->pf_retrans = asoc->pf_retrans;

        /* Initialize the peer's SACK delay timeout based on the
         * association configured value.
         */
        peer->sackdelay = asoc->sackdelay;
        peer->sackfreq = asoc->sackfreq;

        /* Enable/disable heartbeat, SACK delay, and path MTU discovery
         * based on association setting.
         */
        peer->param_flags = asoc->param_flags;

        sctp_transport_route(peer, NULL, sp);

        /* Initialize the pmtu of the transport. */
        if (peer->param_flags & SPP_PMTUD_DISABLE) {
                if (asoc->pathmtu)
                        peer->pathmtu = asoc->pathmtu;
                else
                        peer->pathmtu = SCTP_DEFAULT_MAXSEGMENT;
        }

        /* If this is the first transport addr on this association,
         * initialize the association PMTU to the peer's PMTU.
         * If not and the current association PMTU is higher than the new
         * peer's PMTU, reset the association PMTU to the new peer's PMTU.
         */
        if (asoc->pathmtu)
                asoc->pathmtu = min_t(int, peer->pathmtu, asoc->pathmtu);
        else
                asoc->pathmtu = peer->pathmtu;

        pr_debug("%s: association:%p PMTU set to %d\n", __func__, asoc,
                 asoc->pathmtu);

        peer->pmtu_pending = 0;

        asoc->frag_point = sctp_frag_point(asoc, asoc->pathmtu);

        /* The asoc->peer.port might not be meaningful yet, but
         * initialize the packet structure anyway.
         */
        sctp_packet_init(&peer->packet, peer, asoc->base.bind_addr.port,
                         asoc->peer.port);

        /* 7.2.1 Slow-Start
         *
         * o The initial cwnd before DATA transmission or after a sufficiently
         *   long idle period MUST be set to
         *      min(4*MTU, max(2*MTU, 4380 bytes))
         *
         * o The initial value of ssthresh MAY be arbitrarily high
         *   (for example, implementations MAY use the size of the
         *   receiver advertised window).
         */
        peer->cwnd = min(4*asoc->pathmtu, max_t(__u32, 2*asoc->pathmtu, 4380));

        /* At this point, we may not have the receiver's advertised window,
         * so initialize ssthresh to the default value and it will be set
         * later when we process the INIT.
         */
        peer->ssthresh = SCTP_DEFAULT_MAXWINDOW;

        peer->partial_bytes_acked = 0;
        peer->flight_size = 0;
        peer->burst_limited = 0;

        /* Set the transport's RTO.initial value */
        peer->rto = asoc->rto_initial;
        sctp_max_rto(asoc, peer);

        /* Set the peer's active state. */
        peer->state = peer_state;

        /* Attach the remote transport to our asoc.  */
        list_add_tail_rcu(&peer->transports, &asoc->peer.transport_addr_list);
        asoc->peer.transport_count++;
        /* Add this peer into the transport hashtable */
        sctp_hash_transport(peer);

        /* If we do not yet have a primary path, set one.  */
        if (!asoc->peer.primary_path) {
                sctp_assoc_set_primary(asoc, peer);
                asoc->peer.retran_path = peer;
        }

        if (asoc->peer.active_path == asoc->peer.retran_path &&
            peer->state != SCTP_UNCONFIRMED) {
                asoc->peer.retran_path = peer;
        }

        return peer;
}

/* Delete a transport address from an association.  */
void sctp_assoc_del_peer(struct sctp_association *asoc,
                         const union sctp_addr *addr)
{
        struct list_head        *pos;
        struct list_head        *temp;
        struct sctp_transport   *transport;

        list_for_each_safe(pos, temp, &asoc->peer.transport_addr_list) {
                transport = list_entry(pos, struct sctp_transport, transports);
                if (sctp_cmp_addr_exact(addr, &transport->ipaddr)) {
                        /* Do book keeping for removing the peer and free it. */
                        sctp_assoc_rm_peer(asoc, transport);
                        break;
                }
        }
}

/* Lookup a transport by address. */
struct sctp_transport *sctp_assoc_lookup_paddr(
                                        const struct sctp_association *asoc,
                                        const union sctp_addr *address)
{
        struct sctp_transport *t;

        /* Cycle through all transports searching for a peer address. */

        list_for_each_entry(t, &asoc->peer.transport_addr_list,
                        transports) {
                if (sctp_cmp_addr_exact(address, &t->ipaddr))
                        return t;
        }

        return NULL;
}

/* Remove all transports except a give one */
void sctp_assoc_del_nonprimary_peers(struct sctp_association *asoc,
                                     struct sctp_transport *primary)
{
        struct sctp_transport   *temp;
        struct sctp_transport   *t;

        list_for_each_entry_safe(t, temp, &asoc->peer.transport_addr_list,
                                 transports) {
                /* if the current transport is not the primary one, delete it */
                if (t != primary)
                        sctp_assoc_rm_peer(asoc, t);
        }
}

/* Engage in transport control operations.
 * Mark the transport up or down and send a notification to the user.
 * Select and update the new active and retran paths.
 */
void sctp_assoc_control_transport(struct sctp_association *asoc,
                                  struct sctp_transport *transport,
                                  sctp_transport_cmd_t command,
                                  sctp_sn_error_t error)
{
        struct sctp_ulpevent *event;
        struct sockaddr_storage addr;
        int spc_state = 0;
        bool ulp_notify = true;

        /* Record the transition on the transport.  */
        switch (command) {
        case SCTP_TRANSPORT_UP:
                /* If we are moving from UNCONFIRMED state due
                 * to heartbeat success, report the SCTP_ADDR_CONFIRMED
                 * state to the user, otherwise report SCTP_ADDR_AVAILABLE.
                 */
                if (SCTP_UNCONFIRMED == transport->state &&
                    SCTP_HEARTBEAT_SUCCESS == error)
                        spc_state = SCTP_ADDR_CONFIRMED;
                else
                        spc_state = SCTP_ADDR_AVAILABLE;
                /* Don't inform ULP about transition from PF to
                 * active state and set cwnd to 1 MTU, see SCTP
                 * Quick failover draft section 5.1, point 5
                 */
                if (transport->state == SCTP_PF) {
                        ulp_notify = false;
                        transport->cwnd = asoc->pathmtu;
                }
                transport->state = SCTP_ACTIVE;
                break;

        case SCTP_TRANSPORT_DOWN:
                /* If the transport was never confirmed, do not transition it
                 * to inactive state.  Also, release the cached route since
                 * there may be a better route next time.
                 */
                if (transport->state != SCTP_UNCONFIRMED)
                        transport->state = SCTP_INACTIVE;
                else {
                        dst_release(transport->dst);
                        transport->dst = NULL;
                        ulp_notify = false;
                }

                spc_state = SCTP_ADDR_UNREACHABLE;
                break;

        case SCTP_TRANSPORT_PF:
                transport->state = SCTP_PF;
                ulp_notify = false;
                break;

        default:
                return;
        }

        /* Generate and send a SCTP_PEER_ADDR_CHANGE notification
         * to the user.
         */
        if (ulp_notify) {
                memset(&addr, 0, sizeof(struct sockaddr_storage));
                memcpy(&addr, &transport->ipaddr,
                       transport->af_specific->sockaddr_len);

                event = sctp_ulpevent_make_peer_addr_change(asoc, &addr,
                                        0, spc_state, error, GFP_ATOMIC);
                if (event)
                        sctp_ulpq_tail_event(&asoc->ulpq, event);
        }

        /* Select new active and retran paths. */
        sctp_select_active_and_retran_path(asoc);
}

/* Hold a reference to an association. */
void sctp_association_hold(struct sctp_association *asoc)
{
        atomic_inc(&asoc->base.refcnt);
}

/* Release a reference to an association and cleanup
 * if there are no more references.
 */
void sctp_association_put(struct sctp_association *asoc)
{
        if (atomic_dec_and_test(&asoc->base.refcnt))
                sctp_association_destroy(asoc);
}

/* Allocate the next TSN, Transmission Sequence Number, for the given
 * association.
 */
__u32 sctp_association_get_next_tsn(struct sctp_association *asoc)
{
        /* From Section 1.6 Serial Number Arithmetic:
         * Transmission Sequence Numbers wrap around when they reach
         * 2**32 - 1.  That is, the next TSN a DATA chunk MUST use
         * after transmitting TSN = 2*32 - 1 is TSN = 0.
         */
        __u32 retval = asoc->next_tsn;
        asoc->next_tsn++;
        asoc->unack_data++;

        return retval;
}

/* Compare two addresses to see if they match.  Wildcard addresses
 * only match themselves.
 */
int sctp_cmp_addr_exact(const union sctp_addr *ss1,
                        const union sctp_addr *ss2)
{
        struct sctp_af *af;

        af = sctp_get_af_specific(ss1->sa.sa_family);
        if (unlikely(!af))
                return 0;

        return af->cmp_addr(ss1, ss2);
}

/* Return an ecne chunk to get prepended to a packet.
 * Note:  We are sly and return a shared, prealloced chunk.  FIXME:
 * No we don't, but we could/should.
 */
struct sctp_chunk *sctp_get_ecne_prepend(struct sctp_association *asoc)
{
        if (!asoc->need_ecne)
                return NULL;

        /* Send ECNE if needed.
         * Not being able to allocate a chunk here is not deadly.
         */
        return sctp_make_ecne(asoc, asoc->last_ecne_tsn);
}

/*
 * Find which transport this TSN was sent on.
 */
struct sctp_transport *sctp_assoc_lookup_tsn(struct sctp_association *asoc,
                                             __u32 tsn)
{
        struct sctp_transport *active;
        struct sctp_transport *match;
        struct sctp_transport *transport;
        struct sctp_chunk *chunk;
        __be32 key = htonl(tsn);

        match = NULL;

        /*
         * FIXME: In general, find a more efficient data structure for
         * searching.
         */

        /*
         * The general strategy is to search each transport's transmitted
         * list.   Return which transport this TSN lives on.
         *
         * Let's be hopeful and check the active_path first.
         * Another optimization would be to know if there is only one
         * outbound path and not have to look for the TSN at all.
         *
         */

        active = asoc->peer.active_path;

        list_for_each_entry(chunk, &active->transmitted,
                        transmitted_list) {

                if (key == chunk->subh.data_hdr->tsn) {
                        match = active;
                        goto out;
                }
        }

        /* If not found, go search all the other transports. */
        list_for_each_entry(transport, &asoc->peer.transport_addr_list,
                        transports) {

                if (transport == active)
                        continue;
                list_for_each_entry(chunk, &transport->transmitted,
                                transmitted_list) {
                        if (key == chunk->subh.data_hdr->tsn) {
                                match = transport;
                                goto out;
                        }
                }
        }
out:
        return match;
}

/* Is this the association we are looking for? */
struct sctp_transport *sctp_assoc_is_match(struct sctp_association *asoc,
                                           struct net *net,
                                           const union sctp_addr *laddr,
                                           const union sctp_addr *paddr)
{
        struct sctp_transport *transport;

        if ((htons(asoc->base.bind_addr.port) == laddr->v4.sin_port) &&
            (htons(asoc->peer.port) == paddr->v4.sin_port) &&
            net_eq(sock_net(asoc->base.sk), net)) {
                transport = sctp_assoc_lookup_paddr(asoc, paddr);
                if (!transport)
                        goto out;

                if (sctp_bind_addr_match(&asoc->base.bind_addr, laddr,
                                         sctp_sk(asoc->base.sk)))
                        goto out;
        }
        transport = NULL;

out:
        return transport;
}

/* Do delayed input processing.  This is scheduled by sctp_rcv(). */
static void sctp_assoc_bh_rcv(struct work_struct *work)
{
        struct sctp_association *asoc =
                container_of(work, struct sctp_association,
                             base.inqueue.immediate);
        struct net *net = sock_net(asoc->base.sk);
        struct sctp_endpoint *ep;
        struct sctp_chunk *chunk;
        struct sctp_inq *inqueue;
        int state;
        sctp_subtype_t subtype;
        int error = 0;

        /* The association should be held so we should be safe. */
        ep = asoc->ep;

        inqueue = &asoc->base.inqueue;
        sctp_association_hold(asoc);
        while (NULL != (chunk = sctp_inq_pop(inqueue))) {
                state = asoc->state;
                subtype = SCTP_ST_CHUNK(chunk->chunk_hdr->type);

                /* SCTP-AUTH, Section 6.3:
                 *    The receiver has a list of chunk types which it expects
                 *    to be received only after an AUTH-chunk.  This list has
                 *    been sent to the peer during the association setup.  It
                 *    MUST silently discard these chunks if they are not placed
                 *    after an AUTH chunk in the packet.
                 */
                if (sctp_auth_recv_cid(subtype.chunk, asoc) && !chunk->auth)
                        continue;

                /* Remember where the last DATA chunk came from so we
                 * know where to send the SACK.
                 */
                if (sctp_chunk_is_data(chunk))
                        asoc->peer.last_data_from = chunk->transport;
                else {
                        SCTP_INC_STATS(net, SCTP_MIB_INCTRLCHUNKS);
                        asoc->stats.ictrlchunks++;
                        if (chunk->chunk_hdr->type == SCTP_CID_SACK)
                                asoc->stats.isacks++;
                }

                if (chunk->transport)
                        chunk->transport->last_time_heard = ktime_get();

                /* Run through the state machine. */
                error = sctp_do_sm(net, SCTP_EVENT_T_CHUNK, subtype,
                                   state, ep, asoc, chunk, GFP_ATOMIC);

                /* Check to see if the association is freed in response to
                 * the incoming chunk.  If so, get out of the while loop.
                 */
                if (asoc->base.dead)
                        break;

                /* If there is an error on chunk, discard this packet. */
                if (error && chunk)
                        chunk->pdiscard = 1;
        }
        sctp_association_put(asoc);
}

/* This routine moves an association from its old sk to a new sk.  */
void sctp_assoc_migrate(struct sctp_association *assoc, struct sock *newsk)
{
        struct sctp_sock *newsp = sctp_sk(newsk);
        struct sock *oldsk = assoc->base.sk;

        /* Delete the association from the old endpoint's list of
         * associations.
         */
        list_del_init(&assoc->asocs);

        /* Decrement the backlog value for a TCP-style socket. */
        if (sctp_style(oldsk, TCP))
                oldsk->sk_ack_backlog--;

        /* Release references to the old endpoint and the sock.  */
        sctp_endpoint_put(assoc->ep);
        sock_put(assoc->base.sk);

        /* Get a reference to the new endpoint.  */
        assoc->ep = newsp->ep;
        sctp_endpoint_hold(assoc->ep);

        /* Get a reference to the new sock.  */
        assoc->base.sk = newsk;
        sock_hold(assoc->base.sk);

        /* Add the association to the new endpoint's list of associations.  */
        sctp_endpoint_add_asoc(newsp->ep, assoc);
}

/* Update an association (possibly from unexpected COOKIE-ECHO processing).  */
void sctp_assoc_update(struct sctp_association *asoc,
                       struct sctp_association *new)
{
        struct sctp_transport *trans;
        struct list_head *pos, *temp;

        /* Copy in new parameters of peer. */
        asoc->c = new->c;
        asoc->peer.rwnd = new->peer.rwnd;
        asoc->peer.sack_needed = new->peer.sack_needed;
        asoc->peer.auth_capable = new->peer.auth_capable;
        asoc->peer.i = new->peer.i;
        sctp_tsnmap_init(&asoc->peer.tsn_map, SCTP_TSN_MAP_INITIAL,
                         asoc->peer.i.initial_tsn, GFP_ATOMIC);

        /* Remove any peer addresses not present in the new association. */
        list_for_each_safe(pos, temp, &asoc->peer.transport_addr_list) {
                trans = list_entry(pos, struct sctp_transport, transports);
                if (!sctp_assoc_lookup_paddr(new, &trans->ipaddr)) {
                        sctp_assoc_rm_peer(asoc, trans);
                        continue;
                }

                if (asoc->state >= SCTP_STATE_ESTABLISHED)
                        sctp_transport_reset(trans);
        }

        /* If the case is A (association restart), use
         * initial_tsn as next_tsn. If the case is B, use
         * current next_tsn in case data sent to peer
         * has been discarded and needs retransmission.
         */
        if (asoc->state >= SCTP_STATE_ESTABLISHED) {
                asoc->next_tsn = new->next_tsn;
                asoc->ctsn_ack_point = new->ctsn_ack_point;
                asoc->adv_peer_ack_point = new->adv_peer_ack_point;

                /* Reinitialize SSN for both local streams
                 * and peer's streams.
                 */
                sctp_ssnmap_clear(asoc->ssnmap);

                /* Flush the ULP reassembly and ordered queue.
                 * Any data there will now be stale and will
                 * cause problems.
                 */
                sctp_ulpq_flush(&asoc->ulpq);

                /* reset the overall association error count so
                 * that the restarted association doesn't get torn
                 * down on the next retransmission timer.
                 */
                asoc->overall_error_count = 0;

        } else {
                /* Add any peer addresses from the new association. */
                list_for_each_entry(trans, &new->peer.transport_addr_list,
                                transports) {
                        if (!sctp_assoc_lookup_paddr(asoc, &trans->ipaddr))
                                sctp_assoc_add_peer(asoc, &trans->ipaddr,
                                                    GFP_ATOMIC, trans->state);
                }

                asoc->ctsn_ack_point = asoc->next_tsn - 1;
                asoc->adv_peer_ack_point = asoc->ctsn_ack_point;
                if (!asoc->ssnmap) {
                        /* Move the ssnmap. */
                        asoc->ssnmap = new->ssnmap;
                        new->ssnmap = NULL;
                }

                if (!asoc->assoc_id) {
                        /* get a new association id since we don't have one
                         * yet.
                         */
                        sctp_assoc_set_id(asoc, GFP_ATOMIC);
                }
        }

        /* SCTP-AUTH: Save the peer parameters from the new associations
         * and also move the association shared keys over
         */
        kfree(asoc->peer.peer_random);
        asoc->peer.peer_random = new->peer.peer_random;
        new->peer.peer_random = NULL;

        kfree(asoc->peer.peer_chunks);
        asoc->peer.peer_chunks = new->peer.peer_chunks;
        new->peer.peer_chunks = NULL;

        kfree(asoc->peer.peer_hmacs);
        asoc->peer.peer_hmacs = new->peer.peer_hmacs;
        new->peer.peer_hmacs = NULL;

        sctp_auth_asoc_init_active_key(asoc, GFP_ATOMIC);
}

/* Update the retran path for sending a retransmitted packet.
 * See also RFC4960, 6.4. Multi-Homed SCTP Endpoints:
 *
 *   When there is outbound data to send and the primary path
 *   becomes inactive (e.g., due to failures), or where the
 *   SCTP user explicitly requests to send data to an
 *   inactive destination transport address, before reporting
 *   an error to its ULP, the SCTP endpoint should try to send
 *   the data to an alternate active destination transport
 *   address if one exists.
 *
 *   When retransmitting data that timed out, if the endpoint
 *   is multihomed, it should consider each source-destination
 *   address pair in its retransmission selection policy.
 *   When retransmitting timed-out data, the endpoint should
 *   attempt to pick the most divergent source-destination
 *   pair from the original source-destination pair to which
 *   the packet was transmitted.
 *
 *   Note: Rules for picking the most divergent source-destination
 *   pair are an implementation decision and are not specified
 *   within this document.
 *
 * Our basic strategy is to round-robin transports in priorities
 * according to sctp_trans_score() e.g., if no such
 * transport with state SCTP_ACTIVE exists, round-robin through
 * SCTP_UNKNOWN, etc. You get the picture.
 */
static u8 sctp_trans_score(const struct sctp_transport *trans)
{
        switch (trans->state) {
        case SCTP_ACTIVE:
                return 3;       /* best case */
        case SCTP_UNKNOWN:
                return 2;
        case SCTP_PF:
                return 1;
        default: /* case SCTP_INACTIVE */
                return 0;       /* worst case */
        }
}

static struct sctp_transport *sctp_trans_elect_tie(struct sctp_transport *trans1,
                                                   struct sctp_transport *trans2)
{
        if (trans1->error_count > trans2->error_count) {
                return trans2;
        } else if (trans1->error_count == trans2->error_count &&
                   ktime_after(trans2->last_time_heard,
                               trans1->last_time_heard)) {
                return trans2;
        } else {
                return trans1;
        }
}

static struct sctp_transport *sctp_trans_elect_best(struct sctp_transport *curr,
                                                    struct sctp_transport *best)
{
        u8 score_curr, score_best;

        if (best == NULL || curr == best)
                return curr;

        score_curr = sctp_trans_score(curr);
        score_best = sctp_trans_score(best);

        /* First, try a score-based selection if both transport states
         * differ. If we're in a tie, lets try to make a more clever
         * decision here based on error counts and last time heard.
         */
        if (score_curr > score_best)
                return curr;
        else if (score_curr == score_best)
                return sctp_trans_elect_tie(best, curr);
        else
                return best;
}

void sctp_assoc_update_retran_path(struct sctp_association *asoc)
{
        struct sctp_transport *trans = asoc->peer.retran_path;
        struct sctp_transport *trans_next = NULL;

        /* We're done as we only have the one and only path. */
        if (asoc->peer.transport_count == 1)
                return;
        /* If active_path and retran_path are the same and active,
         * then this is the only active path. Use it.
         */
        if (asoc->peer.active_path == asoc->peer.retran_path &&
            asoc->peer.active_path->state == SCTP_ACTIVE)
                return;

        /* Iterate from retran_path's successor back to retran_path. */
        for (trans = list_next_entry(trans, transports); 1;
             trans = list_next_entry(trans, transports)) {
                /* Manually skip the head element. */
                if (&trans->transports == &asoc->peer.transport_addr_list)
                        continue;
                if (trans->state == SCTP_UNCONFIRMED)
                        continue;
                trans_next = sctp_trans_elect_best(trans, trans_next);
                /* Active is good enough for immediate return. */
                if (trans_next->state == SCTP_ACTIVE)
                        break;
                /* We've reached the end, time to update path. */
                if (trans == asoc->peer.retran_path)
                        break;
        }

        asoc->peer.retran_path = trans_next;

        pr_debug("%s: association:%p updated new path to addr:%pISpc\n",
                 __func__, asoc, &asoc->peer.retran_path->ipaddr.sa);
}

static void sctp_select_active_and_retran_path(struct sctp_association *asoc)
{
        struct sctp_transport *trans, *trans_pri = NULL, *trans_sec = NULL;
        struct sctp_transport *trans_pf = NULL;

        /* Look for the two most recently used active transports. */
        list_for_each_entry(trans, &asoc->peer.transport_addr_list,
                            transports) {
                /* Skip uninteresting transports. */
                if (trans->state == SCTP_INACTIVE ||
                    trans->state == SCTP_UNCONFIRMED)
                        continue;
                /* Keep track of the best PF transport from our
                 * list in case we don't find an active one.
                 */
                if (trans->state == SCTP_PF) {
                        trans_pf = sctp_trans_elect_best(trans, trans_pf);
                        continue;
                }
                /* For active transports, pick the most recent ones. */
                if (trans_pri == NULL ||
                    ktime_after(trans->last_time_heard,
                                trans_pri->last_time_heard)) {
                        trans_sec = trans_pri;
                        trans_pri = trans;
                } else if (trans_sec == NULL ||
                           ktime_after(trans->last_time_heard,
                                       trans_sec->last_time_heard)) {
                        trans_sec = trans;
                }
        }

        /* RFC 2960 6.4 Multi-Homed SCTP Endpoints
         *
         * By default, an endpoint should always transmit to the primary
         * path, unless the SCTP user explicitly specifies the
         * destination transport address (and possibly source transport
         * address) to use. [If the primary is active but not most recent,
         * bump the most recently used transport.]
         */
        if ((asoc->peer.primary_path->state == SCTP_ACTIVE ||
             asoc->peer.primary_path->state == SCTP_UNKNOWN) &&
             asoc->peer.primary_path != trans_pri) {
                trans_sec = trans_pri;
                trans_pri = asoc->peer.primary_path;
        }

        /* We did not find anything useful for a possible retransmission
         * path; either primary path that we found is the the same as
         * the current one, or we didn't generally find an active one.
         */
        if (trans_sec == NULL)
                trans_sec = trans_pri;

        /* If we failed to find a usable transport, just camp on the
         * active or pick a PF iff it's the better choice.
         */
        if (trans_pri == NULL) {
                trans_pri = sctp_trans_elect_best(asoc->peer.active_path, trans_pf);
                trans_sec = trans_pri;
        }

        /* Set the active and retran transports. */
        asoc->peer.active_path = trans_pri;
        asoc->peer.retran_path = trans_sec;
}

struct sctp_transport *
sctp_assoc_choose_alter_transport(struct sctp_association *asoc,
                                  struct sctp_transport *last_sent_to)
{
        /* If this is the first time packet is sent, use the active path,
         * else use the retran path. If the last packet was sent over the
         * retran path, update the retran path and use it.
         */
        if (last_sent_to == NULL) {
                return asoc->peer.active_path;
        } else {
                if (last_sent_to == asoc->peer.retran_path)
                        sctp_assoc_update_retran_path(asoc);

                return asoc->peer.retran_path;
        }
}

/* Update the association's pmtu and frag_point by going through all the
 * transports. This routine is called when a transport's PMTU has changed.
 */
void sctp_assoc_sync_pmtu(struct sock *sk, struct sctp_association *asoc)
{
        struct sctp_transport *t;
        __u32 pmtu = 0;

        if (!asoc)
                return;

        /* Get the lowest pmtu of all the transports. */
        list_for_each_entry(t, &asoc->peer.transport_addr_list,
                                transports) {
                if (t->pmtu_pending && t->dst) {
                        sctp_transport_update_pmtu(sk, t,
                                                   WORD_TRUNC(dst_mtu(t->dst)));
                        t->pmtu_pending = 0;
                }
                if (!pmtu || (t->pathmtu < pmtu))
                        pmtu = t->pathmtu;
        }

        if (pmtu) {
                asoc->pathmtu = pmtu;
                asoc->frag_point = sctp_frag_point(asoc, pmtu);
        }

        pr_debug("%s: asoc:%p, pmtu:%d, frag_point:%d\n", __func__, asoc,
                 asoc->pathmtu, asoc->frag_point);
}

/* Should we send a SACK to update our peer? */
static inline bool sctp_peer_needs_update(struct sctp_association *asoc)
{
        struct net *net = sock_net(asoc->base.sk);
        switch (asoc->state) {
        case SCTP_STATE_ESTABLISHED:
        case SCTP_STATE_SHUTDOWN_PENDING:
        case SCTP_STATE_SHUTDOWN_RECEIVED:
        case SCTP_STATE_SHUTDOWN_SENT:
                if ((asoc->rwnd > asoc->a_rwnd) &&
                    ((asoc->rwnd - asoc->a_rwnd) >= max_t(__u32,
                           (asoc->base.sk->sk_rcvbuf >> net->sctp.rwnd_upd_shift),
                           asoc->pathmtu)))
                        return true;
                break;
        default:
                break;
        }
        return false;
}

/* Increase asoc's rwnd by len and send any window update SACK if needed. */
void sctp_assoc_rwnd_increase(struct sctp_association *asoc, unsigned int len)
{
        struct sctp_chunk *sack;
        struct timer_list *timer;

        if (asoc->rwnd_over) {
                if (asoc->rwnd_over >= len) {
                        asoc->rwnd_over -= len;
                } else {
                        asoc->rwnd += (len - asoc->rwnd_over);
                        asoc->rwnd_over = 0;
                }
        } else {
                asoc->rwnd += len;
        }

        /* If we had window pressure, start recovering it
         * once our rwnd had reached the accumulated pressure
         * threshold.  The idea is to recover slowly, but up
         * to the initial advertised window.
         */
        if (asoc->rwnd_press && asoc->rwnd >= asoc->rwnd_press) {
                int change = min(asoc->pathmtu, asoc->rwnd_press);
                asoc->rwnd += change;
                asoc->rwnd_press -= change;
        }

        pr_debug("%s: asoc:%p rwnd increased by %d to (%u, %u) - %u\n",
                 __func__, asoc, len, asoc->rwnd, asoc->rwnd_over,
                 asoc->a_rwnd);

        /* Send a window update SACK if the rwnd has increased by at least the
         * minimum of the association's PMTU and half of the receive buffer.
         * The algorithm used is similar to the one described in
         * Section 4.2.3.3 of RFC 1122.
         */
        if (sctp_peer_needs_update(asoc)) {
                asoc->a_rwnd = asoc->rwnd;

                pr_debug("%s: sending window update SACK- asoc:%p rwnd:%u "
                         "a_rwnd:%u\n", __func__, asoc, asoc->rwnd,
                         asoc->a_rwnd);

                sack = sctp_make_sack(asoc);
                if (!sack)
                        return;

                asoc->peer.sack_needed = 0;

                sctp_outq_tail(&asoc->outqueue, sack, GFP_ATOMIC);

                /* Stop the SACK timer.  */
                timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];
                if (del_timer(timer))
                        sctp_association_put(asoc);
        }
}

/* Decrease asoc's rwnd by len. */
void sctp_assoc_rwnd_decrease(struct sctp_association *asoc, unsigned int len)
{
        int rx_count;
        int over = 0;

        if (unlikely(!asoc->rwnd || asoc->rwnd_over))
                pr_debug("%s: association:%p has asoc->rwnd:%u, "
                         "asoc->rwnd_over:%u!\n", __func__, asoc,
                         asoc->rwnd, asoc->rwnd_over);

        if (asoc->ep->rcvbuf_policy)
                rx_count = atomic_read(&asoc->rmem_alloc);
        else
                rx_count = atomic_read(&asoc->base.sk->sk_rmem_alloc);

        /* If we've reached or overflowed our receive buffer, announce
         * a 0 rwnd if rwnd would still be positive.  Store the
         * the potential pressure overflow so that the window can be restored
         * back to original value.
         */
        if (rx_count >= asoc->base.sk->sk_rcvbuf)
                over = 1;

        if (asoc->rwnd >= len) {
                asoc->rwnd -= len;
                if (over) {
                        asoc->rwnd_press += asoc->rwnd;
                        asoc->rwnd = 0;
                }
        } else {
                asoc->rwnd_over = len - asoc->rwnd;
                asoc->rwnd = 0;
        }

        pr_debug("%s: asoc:%p rwnd decreased by %d to (%u, %u, %u)\n",
                 __func__, asoc, len, asoc->rwnd, asoc->rwnd_over,
                 asoc->rwnd_press);
}

/* Build the bind address list for the association based on info from the
 * local endpoint and the remote peer.
 */
int sctp_assoc_set_bind_addr_from_ep(struct sctp_association *asoc,
                                     sctp_scope_t scope, gfp_t gfp)
{
        int flags;

        /* Use scoping rules to determine the subset of addresses from
         * the endpoint.
         */
        flags = (PF_INET6 == asoc->base.sk->sk_family) ? SCTP_ADDR6_ALLOWED : 0;
        if (asoc->peer.ipv4_address)
                flags |= SCTP_ADDR4_PEERSUPP;
        if (asoc->peer.ipv6_address)
                flags |= SCTP_ADDR6_PEERSUPP;

        return sctp_bind_addr_copy(sock_net(asoc->base.sk),
                                   &asoc->base.bind_addr,
                                   &asoc->ep->base.bind_addr,
                                   scope, gfp, flags);
}

/* Build the association's bind address list from the cookie.  */
int sctp_assoc_set_bind_addr_from_cookie(struct sctp_association *asoc,
                                         struct sctp_cookie *cookie,
                                         gfp_t gfp)
{
        int var_size2 = ntohs(cookie->peer_init->chunk_hdr.length);
        int var_size3 = cookie->raw_addr_list_len;
        __u8 *raw = (__u8 *)cookie->peer_init + var_size2;

        return sctp_raw_to_bind_addrs(&asoc->base.bind_addr, raw, var_size3,
                                      asoc->ep->base.bind_addr.port, gfp);
}

/* Lookup laddr in the bind address list of an association. */
int sctp_assoc_lookup_laddr(struct sctp_association *asoc,
                            const union sctp_addr *laddr)
{
        int found = 0;

        if ((asoc->base.bind_addr.port == ntohs(laddr->v4.sin_port)) &&
            sctp_bind_addr_match(&asoc->base.bind_addr, laddr,
                                 sctp_sk(asoc->base.sk)))
                found = 1;

        return found;
}

/* Set an association id for a given association */
int sctp_assoc_set_id(struct sctp_association *asoc, gfp_t gfp)
{
        bool preload = gfpflags_allow_blocking(gfp);
        int ret;

        /* If the id is already assigned, keep it. */
        if (asoc->assoc_id)
                return 0;

        if (preload)
                idr_preload(gfp);
        spin_lock_bh(&sctp_assocs_id_lock);
        /* 0 is not a valid assoc_id, must be >= 1 */
        ret = idr_alloc_cyclic(&sctp_assocs_id, asoc, 1, 0, GFP_NOWAIT);
        spin_unlock_bh(&sctp_assocs_id_lock);
        if (preload)
                idr_preload_end();
        if (ret < 0)
                return ret;

        asoc->assoc_id = (sctp_assoc_t)ret;
        return 0;
}

/* Free the ASCONF queue */
static void sctp_assoc_free_asconf_queue(struct sctp_association *asoc)
{
        struct sctp_chunk *asconf;
        struct sctp_chunk *tmp;

        list_for_each_entry_safe(asconf, tmp, &asoc->addip_chunk_list, list) {
                list_del_init(&asconf->list);
                sctp_chunk_free(asconf);
        }
}

/* Free asconf_ack cache */
static void sctp_assoc_free_asconf_acks(struct sctp_association *asoc)
{
        struct sctp_chunk *ack;
        struct sctp_chunk *tmp;

        list_for_each_entry_safe(ack, tmp, &asoc->asconf_ack_list,
                                transmitted_list) {
                list_del_init(&ack->transmitted_list);
                sctp_chunk_free(ack);
        }
}

/* Clean up the ASCONF_ACK queue */
void sctp_assoc_clean_asconf_ack_cache(const struct sctp_association *asoc)
{
        struct sctp_chunk *ack;
        struct sctp_chunk *tmp;

        /* We can remove all the entries from the queue up to
         * the "Peer-Sequence-Number".
         */
        list_for_each_entry_safe(ack, tmp, &asoc->asconf_ack_list,
                                transmitted_list) {
                if (ack->subh.addip_hdr->serial ==
                                htonl(asoc->peer.addip_serial))
                        break;

                list_del_init(&ack->transmitted_list);
                sctp_chunk_free(ack);
        }
}

/* Find the ASCONF_ACK whose serial number matches ASCONF */
struct sctp_chunk *sctp_assoc_lookup_asconf_ack(
                                        const struct sctp_association *asoc,
                                        __be32 serial)
{
        struct sctp_chunk *ack;

        /* Walk through the list of cached ASCONF-ACKs and find the
         * ack chunk whose serial number matches that of the request.
         */
        list_for_each_entry(ack, &asoc->asconf_ack_list, transmitted_list) {
                if (sctp_chunk_pending(ack))
                        continue;
                if (ack->subh.addip_hdr->serial == serial) {
                        sctp_chunk_hold(ack);
                        return ack;
                }
        }

        return NULL;
}

void sctp_asconf_queue_teardown(struct sctp_association *asoc)
{
        /* Free any cached ASCONF_ACK chunk. */
        sctp_assoc_free_asconf_acks(asoc);

        /* Free the ASCONF queue. */
        sctp_assoc_free_asconf_queue(asoc);

        /* Free any cached ASCONF chunk. */
        if (asoc->addip_last_asconf)
                sctp_chunk_free(asoc->addip_last_asconf);
}