input.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 Nokia, Inc.
 * Copyright (c) 2001 La Monte H.P. Yarroll
 *
 * This file is part of the SCTP kernel implementation
 *
 * These functions handle all input from the IP layer into SCTP.
 *
 * 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]>
 *    Xingang Guo <[email protected]>
 *    Jon Grimm <[email protected]>
 *    Hui Huang <[email protected]>
 *    Daisy Chang <[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.
 */

#include <linux/types.h>
#include <linux/list.h> /* For struct list_head */
#include <linux/socket.h>
#include <linux/ip.h>
#include <linux/time.h> /* For struct timeval */
#include <linux/slab.h>
#include <net/ip.h>
#include <net/icmp.h>
#include <net/snmp.h>
#include <net/sock.h>
#include <net/xfrm.h>
#include <net/sctp/sctp.h>
#include <net/sctp/sm.h>
#include <net/sctp/checksum.h>
#include <net/net_namespace.h>

/* Forward declarations for internal helpers. */
static int sctp_rcv_ootb(struct sk_buff *);
static struct sctp_association *__sctp_rcv_lookup(struct net *net,
                      struct sk_buff *skb,
                      const union sctp_addr *paddr,
                      const union sctp_addr *laddr,
                      struct sctp_transport **transportp);
static struct sctp_endpoint *__sctp_rcv_lookup_endpoint(struct net *net,
                        const union sctp_addr *laddr);
static struct sctp_association *__sctp_lookup_association(
                    struct net *net,
                    const union sctp_addr *local,
                    const union sctp_addr *peer,
                    struct sctp_transport **pt);

static int sctp_add_backlog(struct sock *sk, struct sk_buff *skb);


/* Calculate the SCTP checksum of an SCTP packet.  */
static inline int sctp_rcv_checksum(struct net *net, struct sk_buff *skb)
{
    struct sctphdr *sh = sctp_hdr(skb);
    __le32 cmp = sh->checksum;
    struct sk_buff *list;
    __le32 val;
    __u32 tmp = sctp_start_cksum((__u8 *)sh, skb_headlen(skb));

    skb_walk_frags(skb, list)
        tmp = sctp_update_cksum((__u8 *)list->data, skb_headlen(list),
                    tmp);

    val = sctp_end_cksum(tmp);

    if (val != cmp) {
        /* CRC failure, dump it. */
        SCTP_INC_STATS_BH(net, SCTP_MIB_CHECKSUMERRORS);
        return -1;
    }
    return 0;
}

struct sctp_input_cb {
    union {
        struct inet_skb_parm    h4;
#if IS_ENABLED(CONFIG_IPV6)
        struct inet6_skb_parm   h6;
#endif
    } header;
    struct sctp_chunk *chunk;
};
#define SCTP_INPUT_CB(__skb)    ((struct sctp_input_cb *)&((__skb)->cb[0]))

/*
 * This is the routine which IP calls when receiving an SCTP packet.
 */
int sctp_rcv(struct sk_buff *skb)
{
    struct sock *sk;
    struct sctp_association *asoc;
    struct sctp_endpoint *ep = NULL;
    struct sctp_ep_common *rcvr;
    struct sctp_transport *transport = NULL;
    struct sctp_chunk *chunk;
    struct sctphdr *sh;
    union sctp_addr src;
    union sctp_addr dest;
    int family;
    struct sctp_af *af;
    struct net *net = dev_net(skb->dev);

    if (skb->pkt_type!=PACKET_HOST)
        goto discard_it;

    SCTP_INC_STATS_BH(net, SCTP_MIB_INSCTPPACKS);

    if (skb_linearize(skb))
        goto discard_it;

    sh = sctp_hdr(skb);

    /* Pull up the IP and SCTP headers. */
    __skb_pull(skb, skb_transport_offset(skb));
    if (skb->len < sizeof(struct sctphdr))
        goto discard_it;
    if (!sctp_checksum_disable && !skb_csum_unnecessary(skb) &&
          sctp_rcv_checksum(net, skb) < 0)
        goto discard_it;

    skb_pull(skb, sizeof(struct sctphdr));

    /* Make sure we at least have chunk headers worth of data left. */
    if (skb->len < sizeof(struct sctp_chunkhdr))
        goto discard_it;

    family = ipver2af(ip_hdr(skb)->version);
    af = sctp_get_af_specific(family);
    if (unlikely(!af))
        goto discard_it;

    /* Initialize local addresses for lookups. */
    af->from_skb(&src, skb, 1);
    af->from_skb(&dest, skb, 0);

    /* If the packet is to or from a non-unicast address,
     * silently discard the packet.
     *
     * This is not clearly defined in the RFC except in section
     * 8.4 - OOTB handling.  However, based on the book "Stream Control
     * Transmission Protocol" 2.1, "It is important to note that the
     * IP address of an SCTP transport address must be a routable
     * unicast address.  In other words, IP multicast addresses and
     * IP broadcast addresses cannot be used in an SCTP transport
     * address."
     */
    if (!af->addr_valid(&src, NULL, skb) ||
        !af->addr_valid(&dest, NULL, skb))
        goto discard_it;

    asoc = __sctp_rcv_lookup(net, skb, &src, &dest, &transport);

    if (!asoc)
        ep = __sctp_rcv_lookup_endpoint(net, &dest);

    /* Retrieve the common input handling substructure. */
    rcvr = asoc ? &asoc->base : &ep->base;
    sk = rcvr->sk;

    /*
     * If a frame arrives on an interface and the receiving socket is
     * bound to another interface, via SO_BINDTODEVICE, treat it as OOTB
     */
    if (sk->sk_bound_dev_if && (sk->sk_bound_dev_if != af->skb_iif(skb)))
    {
        if (asoc) {
            sctp_association_put(asoc);
            asoc = NULL;
        } else {
            sctp_endpoint_put(ep);
            ep = NULL;
        }
        sk = net->sctp.ctl_sock;
        ep = sctp_sk(sk)->ep;
        sctp_endpoint_hold(ep);
        rcvr = &ep->base;
    }

    /*
     * RFC 2960, 8.4 - Handle "Out of the blue" Packets.
     * An SCTP packet is called an "out of the blue" (OOTB)
     * packet if it is correctly formed, i.e., passed the
     * receiver's checksum check, but the receiver is not
     * able to identify the association to which this
     * packet belongs.
     */
    if (!asoc) {
        if (sctp_rcv_ootb(skb)) {
            SCTP_INC_STATS_BH(net, SCTP_MIB_OUTOFBLUES);
            goto discard_release;
        }
    }

    if (!xfrm_policy_check(sk, XFRM_POLICY_IN, skb, family))
        goto discard_release;
    nf_reset(skb);

    if (sk_filter(sk, skb))
        goto discard_release;

    /* Create an SCTP packet structure. */
    chunk = sctp_chunkify(skb, asoc, sk);
    if (!chunk)
        goto discard_release;
    SCTP_INPUT_CB(skb)->chunk = chunk;

    /* Remember what endpoint is to handle this packet. */
    chunk->rcvr = rcvr;

    /* Remember the SCTP header. */
    chunk->sctp_hdr = sh;

    /* Set the source and destination addresses of the incoming chunk.  */
    sctp_init_addrs(chunk, &src, &dest);

    /* Remember where we came from.  */
    chunk->transport = transport;

    /* Acquire access to the sock lock. Note: We are safe from other
     * bottom halves on this lock, but a user may be in the lock too,
     * so check if it is busy.
     */
    sctp_bh_lock_sock(sk);

    if (sk != rcvr->sk) {
        /* Our cached sk is different from the rcvr->sk.  This is
         * because migrate()/accept() may have moved the association
         * to a new socket and released all the sockets.  So now we
         * are holding a lock on the old socket while the user may
         * be doing something with the new socket.  Switch our veiw
         * of the current sk.
         */
        sctp_bh_unlock_sock(sk);
        sk = rcvr->sk;
        sctp_bh_lock_sock(sk);
    }

    if (sock_owned_by_user(sk)) {
        if (sctp_add_backlog(sk, skb)) {
            sctp_bh_unlock_sock(sk);
            sctp_chunk_free(chunk);
            skb = NULL; /* sctp_chunk_free already freed the skb */
            goto discard_release;
        }
        SCTP_INC_STATS_BH(net, SCTP_MIB_IN_PKT_BACKLOG);
    } else {
        SCTP_INC_STATS_BH(net, SCTP_MIB_IN_PKT_SOFTIRQ);
        sctp_inq_push(&chunk->rcvr->inqueue, chunk);
    }

    sctp_bh_unlock_sock(sk);

    /* Release the asoc/ep ref we took in the lookup calls. */
    if (asoc)
        sctp_association_put(asoc);
    else
        sctp_endpoint_put(ep);

    return 0;

discard_it:
    SCTP_INC_STATS_BH(net, SCTP_MIB_IN_PKT_DISCARDS);
    kfree_skb(skb);
    return 0;

discard_release:
    /* Release the asoc/ep ref we took in the lookup calls. */
    if (asoc)
        sctp_association_put(asoc);
    else
        sctp_endpoint_put(ep);

    goto discard_it;
}

/* Process the backlog queue of the socket.  Every skb on
 * the backlog holds a ref on an association or endpoint.
 * We hold this ref throughout the state machine to make
 * sure that the structure we need is still around.
 */
int sctp_backlog_rcv(struct sock *sk, struct sk_buff *skb)
{
    struct sctp_chunk *chunk = SCTP_INPUT_CB(skb)->chunk;
    struct sctp_inq *inqueue = &chunk->rcvr->inqueue;
    struct sctp_ep_common *rcvr = NULL;
    int backloged = 0;

    rcvr = chunk->rcvr;

    /* If the rcvr is dead then the association or endpoint
     * has been deleted and we can safely drop the chunk
     * and refs that we are holding.
     */
    if (rcvr->dead) {
        sctp_chunk_free(chunk);
        goto done;
    }

    if (unlikely(rcvr->sk != sk)) {
        /* In this case, the association moved from one socket to
         * another.  We are currently sitting on the backlog of the
         * old socket, so we need to move.
         * However, since we are here in the process context we
         * need to take make sure that the user doesn't own
         * the new socket when we process the packet.
         * If the new socket is user-owned, queue the chunk to the
         * backlog of the new socket without dropping any refs.
         * Otherwise, we can safely push the chunk on the inqueue.
         */

        sk = rcvr->sk;
        sctp_bh_lock_sock(sk);

        if (sock_owned_by_user(sk)) {
            if (sk_add_backlog(sk, skb, sk->sk_rcvbuf))
                sctp_chunk_free(chunk);
            else
                backloged = 1;
        } else
            sctp_inq_push(inqueue, chunk);

        sctp_bh_unlock_sock(sk);

        /* If the chunk was backloged again, don't drop refs */
        if (backloged)
            return 0;
    } else {
        sctp_inq_push(inqueue, chunk);
    }

done:
    /* Release the refs we took in sctp_add_backlog */
    if (SCTP_EP_TYPE_ASSOCIATION == rcvr->type)
        sctp_association_put(sctp_assoc(rcvr));
    else if (SCTP_EP_TYPE_SOCKET == rcvr->type)
        sctp_endpoint_put(sctp_ep(rcvr));
    else
        BUG();

    return 0;
}

static int sctp_add_backlog(struct sock *sk, struct sk_buff *skb)
{
    struct sctp_chunk *chunk = SCTP_INPUT_CB(skb)->chunk;
    struct sctp_ep_common *rcvr = chunk->rcvr;
    int ret;

    ret = sk_add_backlog(sk, skb, sk->sk_rcvbuf);
    if (!ret) {
        /* Hold the assoc/ep while hanging on the backlog queue.
         * This way, we know structures we need will not disappear
         * from us
         */
        if (SCTP_EP_TYPE_ASSOCIATION == rcvr->type)
            sctp_association_hold(sctp_assoc(rcvr));
        else if (SCTP_EP_TYPE_SOCKET == rcvr->type)
            sctp_endpoint_hold(sctp_ep(rcvr));
        else
            BUG();
    }
    return ret;

}

/* Handle icmp frag needed error. */
void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc,
               struct sctp_transport *t, __u32 pmtu)
{
    if (!t || (t->pathmtu <= pmtu))
        return;

    if (sock_owned_by_user(sk)) {
        asoc->pmtu_pending = 1;
        t->pmtu_pending = 1;
        return;
    }

    if (t->param_flags & SPP_PMTUD_ENABLE) {
        /* Update transports view of the MTU */
        sctp_transport_update_pmtu(sk, t, pmtu);

        /* Update association pmtu. */
        sctp_assoc_sync_pmtu(sk, asoc);
    }

    /* Retransmit with the new pmtu setting.
     * Normally, if PMTU discovery is disabled, an ICMP Fragmentation
     * Needed will never be sent, but if a message was sent before
     * PMTU discovery was disabled that was larger than the PMTU, it
     * would not be fragmented, so it must be re-transmitted fragmented.
     */
    sctp_retransmit(&asoc->outqueue, t, SCTP_RTXR_PMTUD);
}

void sctp_icmp_redirect(struct sock *sk, struct sctp_transport *t,
            struct sk_buff *skb)
{
    struct dst_entry *dst;

    if (!t)
        return;
    dst = sctp_transport_dst_check(t);
    if (dst)
        dst->ops->redirect(dst, sk, skb);
}

/*
 * SCTP Implementer's Guide, 2.37 ICMP handling procedures
 *
 * ICMP8) If the ICMP code is a "Unrecognized next header type encountered"
 *        or a "Protocol Unreachable" treat this message as an abort
 *        with the T bit set.
 *
 * This function sends an event to the state machine, which will abort the
 * association.
 *
 */
void sctp_icmp_proto_unreachable(struct sock *sk,
               struct sctp_association *asoc,
               struct sctp_transport *t)
{
    SCTP_DEBUG_PRINTK("%s\n",  __func__);

    if (sock_owned_by_user(sk)) {
        if (timer_pending(&t->proto_unreach_timer))
            return;
        else {
            if (!mod_timer(&t->proto_unreach_timer,
                        jiffies + (HZ/20)))
                sctp_association_hold(asoc);
        }
            
    } else {
        struct net *net = sock_net(sk);

        if (timer_pending(&t->proto_unreach_timer) &&
            del_timer(&t->proto_unreach_timer))
            sctp_association_put(asoc);

        sctp_do_sm(net, SCTP_EVENT_T_OTHER,
               SCTP_ST_OTHER(SCTP_EVENT_ICMP_PROTO_UNREACH),
               asoc->state, asoc->ep, asoc, t,
               GFP_ATOMIC);
    }
}

/* Common lookup code for icmp/icmpv6 error handler. */
struct sock *sctp_err_lookup(struct net *net, int family, struct sk_buff *skb,
                 struct sctphdr *sctphdr,
                 struct sctp_association **app,
                 struct sctp_transport **tpp)
{
    union sctp_addr saddr;
    union sctp_addr daddr;
    struct sctp_af *af;
    struct sock *sk = NULL;
    struct sctp_association *asoc;
    struct sctp_transport *transport = NULL;
    struct sctp_init_chunk *chunkhdr;
    __u32 vtag = ntohl(sctphdr->vtag);
    int len = skb->len - ((void *)sctphdr - (void *)skb->data);

    *app = NULL; *tpp = NULL;

    af = sctp_get_af_specific(family);
    if (unlikely(!af)) {
        return NULL;
    }

    /* Initialize local addresses for lookups. */
    af->from_skb(&saddr, skb, 1);
    af->from_skb(&daddr, skb, 0);

    /* Look for an association that matches the incoming ICMP error
     * packet.
     */
    asoc = __sctp_lookup_association(net, &saddr, &daddr, &transport);
    if (!asoc)
        return NULL;

    sk = asoc->base.sk;

    /* RFC 4960, Appendix C. ICMP Handling
     *
     * ICMP6) An implementation MUST validate that the Verification Tag
     * contained in the ICMP message matches the Verification Tag of
     * the peer.  If the Verification Tag is not 0 and does NOT
     * match, discard the ICMP message.  If it is 0 and the ICMP
     * message contains enough bytes to verify that the chunk type is
     * an INIT chunk and that the Initiate Tag matches the tag of the
     * peer, continue with ICMP7.  If the ICMP message is too short
     * or the chunk type or the Initiate Tag does not match, silently
     * discard the packet.
     */
    if (vtag == 0) {
        chunkhdr = (void *)sctphdr + sizeof(struct sctphdr);
        if (len < sizeof(struct sctphdr) + sizeof(sctp_chunkhdr_t)
              + sizeof(__be32) ||
            chunkhdr->chunk_hdr.type != SCTP_CID_INIT ||
            ntohl(chunkhdr->init_hdr.init_tag) != asoc->c.my_vtag) {
            goto out;
        }
    } else if (vtag != asoc->c.peer_vtag) {
        goto out;
    }

    sctp_bh_lock_sock(sk);

    /* If too many ICMPs get dropped on busy
     * servers this needs to be solved differently.
     */
    if (sock_owned_by_user(sk))
        NET_INC_STATS_BH(net, LINUX_MIB_LOCKDROPPEDICMPS);

    *app = asoc;
    *tpp = transport;
    return sk;

out:
    if (asoc)
        sctp_association_put(asoc);
    return NULL;
}

/* Common cleanup code for icmp/icmpv6 error handler. */
void sctp_err_finish(struct sock *sk, struct sctp_association *asoc)
{
    sctp_bh_unlock_sock(sk);
    if (asoc)
        sctp_association_put(asoc);
}

/*
 * This routine is called by the ICMP module when it gets some
 * sort of error condition.  If err < 0 then the socket should
 * be closed and the error returned to the user.  If err > 0
 * it's just the icmp type << 8 | icmp code.  After adjustment
 * header points to the first 8 bytes of the sctp header.  We need
 * to find the appropriate port.
 *
 * The locking strategy used here is very "optimistic". When
 * someone else accesses the socket the ICMP is just dropped
 * and for some paths there is no check at all.
 * A more general error queue to queue errors for later handling
 * is probably better.
 *
 */
void sctp_v4_err(struct sk_buff *skb, __u32 info)
{
    const struct iphdr *iph = (const struct iphdr *)skb->data;
    const int ihlen = iph->ihl * 4;
    const int type = icmp_hdr(skb)->type;
    const int code = icmp_hdr(skb)->code;
    struct sock *sk;
    struct sctp_association *asoc = NULL;
    struct sctp_transport *transport;
    struct inet_sock *inet;
    sk_buff_data_t saveip, savesctp;
    int err;
    struct net *net = dev_net(skb->dev);

    if (skb->len < ihlen + 8) {
        ICMP_INC_STATS_BH(net, ICMP_MIB_INERRORS);
        return;
    }

    /* Fix up skb to look at the embedded net header. */
    saveip = skb->network_header;
    savesctp = skb->transport_header;
    skb_reset_network_header(skb);
    skb_set_transport_header(skb, ihlen);
    sk = sctp_err_lookup(net, AF_INET, skb, sctp_hdr(skb), &asoc, &transport);
    /* Put back, the original values. */
    skb->network_header = saveip;
    skb->transport_header = savesctp;
    if (!sk) {
        ICMP_INC_STATS_BH(net, ICMP_MIB_INERRORS);
        return;
    }
    /* Warning:  The sock lock is held.  Remember to call
     * sctp_err_finish!
     */

    switch (type) {
    case ICMP_PARAMETERPROB:
        err = EPROTO;
        break;
    case ICMP_DEST_UNREACH:
        if (code > NR_ICMP_UNREACH)
            goto out_unlock;

        /* PMTU discovery (RFC1191) */
        if (ICMP_FRAG_NEEDED == code) {
            sctp_icmp_frag_needed(sk, asoc, transport, info);
            goto out_unlock;
        }
        else {
            if (ICMP_PROT_UNREACH == code) {
                sctp_icmp_proto_unreachable(sk, asoc,
                                transport);
                goto out_unlock;
            }
        }
        err = icmp_err_convert[code].errno;
        break;
    case ICMP_TIME_EXCEEDED:
        /* Ignore any time exceeded errors due to fragment reassembly
         * timeouts.
         */
        if (ICMP_EXC_FRAGTIME == code)
            goto out_unlock;

        err = EHOSTUNREACH;
        break;
    case ICMP_REDIRECT:
        sctp_icmp_redirect(sk, transport, skb);
        err = 0;
        break;
    default:
        goto out_unlock;
    }

    inet = inet_sk(sk);
    if (!sock_owned_by_user(sk) && inet->recverr) {
        sk->sk_err = err;
        sk->sk_error_report(sk);
    } else {  /* Only an error on timeout */
        sk->sk_err_soft = err;
    }

out_unlock:
    sctp_err_finish(sk, asoc);
}

/*
 * RFC 2960, 8.4 - Handle "Out of the blue" Packets.
 *
 * This function scans all the chunks in the OOTB packet to determine if
 * the packet should be discarded right away.  If a response might be needed
 * for this packet, or, if further processing is possible, the packet will
 * be queued to a proper inqueue for the next phase of handling.
 *
 * Output:
 * Return 0 - If further processing is needed.
 * Return 1 - If the packet can be discarded right away.
 */
static int sctp_rcv_ootb(struct sk_buff *skb)
{
    sctp_chunkhdr_t *ch;
    __u8 *ch_end;

    ch = (sctp_chunkhdr_t *) skb->data;

    /* Scan through all the chunks in the packet.  */
    do {
        /* Break out if chunk length is less then minimal. */
        if (ntohs(ch->length) < sizeof(sctp_chunkhdr_t))
            break;

        ch_end = ((__u8 *)ch) + WORD_ROUND(ntohs(ch->length));
        if (ch_end > skb_tail_pointer(skb))
            break;

        /* RFC 8.4, 2) If the OOTB packet contains an ABORT chunk, the
         * receiver MUST silently discard the OOTB packet and take no
         * further action.
         */
        if (SCTP_CID_ABORT == ch->type)
            goto discard;

        /* RFC 8.4, 6) If the packet contains a SHUTDOWN COMPLETE
         * chunk, the receiver should silently discard the packet
         * and take no further action.
         */
        if (SCTP_CID_SHUTDOWN_COMPLETE == ch->type)
            goto discard;

        /* RFC 4460, 2.11.2
         * This will discard packets with INIT chunk bundled as
         * subsequent chunks in the packet.  When INIT is first,
         * the normal INIT processing will discard the chunk.
         */
        if (SCTP_CID_INIT == ch->type && (void *)ch != skb->data)
            goto discard;

        ch = (sctp_chunkhdr_t *) ch_end;
    } while (ch_end < skb_tail_pointer(skb));

    return 0;

discard:
    return 1;
}

/* Insert endpoint into the hash table.  */
static void __sctp_hash_endpoint(struct sctp_endpoint *ep)
{
    struct net *net = sock_net(ep->base.sk);
    struct sctp_ep_common *epb;
    struct sctp_hashbucket *head;

    epb = &ep->base;

    epb->hashent = sctp_ep_hashfn(net, epb->bind_addr.port);
    head = &sctp_ep_hashtable[epb->hashent];

    sctp_write_lock(&head->lock);
    hlist_add_head(&epb->node, &head->chain);
    sctp_write_unlock(&head->lock);
}

/* Add an endpoint to the hash. Local BH-safe. */
void sctp_hash_endpoint(struct sctp_endpoint *ep)
{
    sctp_local_bh_disable();
    __sctp_hash_endpoint(ep);
    sctp_local_bh_enable();
}

/* Remove endpoint from the hash table.  */
static void __sctp_unhash_endpoint(struct sctp_endpoint *ep)
{
    struct net *net = sock_net(ep->base.sk);
    struct sctp_hashbucket *head;
    struct sctp_ep_common *epb;

    epb = &ep->base;

    epb->hashent = sctp_ep_hashfn(net, epb->bind_addr.port);

    head = &sctp_ep_hashtable[epb->hashent];

    sctp_write_lock(&head->lock);
    hlist_del_init(&epb->node);
    sctp_write_unlock(&head->lock);
}

/* Remove endpoint from the hash.  Local BH-safe. */
void sctp_unhash_endpoint(struct sctp_endpoint *ep)
{
    sctp_local_bh_disable();
    __sctp_unhash_endpoint(ep);
    sctp_local_bh_enable();
}

/* Look up an endpoint. */
static struct sctp_endpoint *__sctp_rcv_lookup_endpoint(struct net *net,
                        const union sctp_addr *laddr)
{
    struct sctp_hashbucket *head;
    struct sctp_ep_common *epb;
    struct sctp_endpoint *ep;
    struct hlist_node *node;
    int hash;

    hash = sctp_ep_hashfn(net, ntohs(laddr->v4.sin_port));
    head = &sctp_ep_hashtable[hash];
    read_lock(&head->lock);
    sctp_for_each_hentry(epb, node, &head->chain) {
        ep = sctp_ep(epb);
        if (sctp_endpoint_is_match(ep, net, laddr))
            goto hit;
    }

    ep = sctp_sk(net->sctp.ctl_sock)->ep;

hit:
    sctp_endpoint_hold(ep);
    read_unlock(&head->lock);
    return ep;
}

/* Insert association into the hash table.  */
static void __sctp_hash_established(struct sctp_association *asoc)
{
    struct net *net = sock_net(asoc->base.sk);
    struct sctp_ep_common *epb;
    struct sctp_hashbucket *head;

    epb = &asoc->base;

    /* Calculate which chain this entry will belong to. */
    epb->hashent = sctp_assoc_hashfn(net, epb->bind_addr.port,
                     asoc->peer.port);

    head = &sctp_assoc_hashtable[epb->hashent];

    sctp_write_lock(&head->lock);
    hlist_add_head(&epb->node, &head->chain);
    sctp_write_unlock(&head->lock);
}

/* Add an association to the hash. Local BH-safe. */
void sctp_hash_established(struct sctp_association *asoc)
{
    if (asoc->temp)
        return;

    sctp_local_bh_disable();
    __sctp_hash_established(asoc);
    sctp_local_bh_enable();
}

/* Remove association from the hash table.  */
static void __sctp_unhash_established(struct sctp_association *asoc)
{
    struct net *net = sock_net(asoc->base.sk);
    struct sctp_hashbucket *head;
    struct sctp_ep_common *epb;

    epb = &asoc->base;

    epb->hashent = sctp_assoc_hashfn(net, epb->bind_addr.port,
                     asoc->peer.port);

    head = &sctp_assoc_hashtable[epb->hashent];

    sctp_write_lock(&head->lock);
    hlist_del_init(&epb->node);
    sctp_write_unlock(&head->lock);
}

/* Remove association from the hash table.  Local BH-safe. */
void sctp_unhash_established(struct sctp_association *asoc)
{
    if (asoc->temp)
        return;

    sctp_local_bh_disable();
    __sctp_unhash_established(asoc);
    sctp_local_bh_enable();
}

/* Look up an association. */
static struct sctp_association *__sctp_lookup_association(
                    struct net *net,
                    const union sctp_addr *local,
                    const union sctp_addr *peer,
                    struct sctp_transport **pt)
{
    struct sctp_hashbucket *head;
    struct sctp_ep_common *epb;
    struct sctp_association *asoc;
    struct sctp_transport *transport;
    struct hlist_node *node;
    int hash;

    /* Optimize here for direct hit, only listening connections can
     * have wildcards anyways.
     */
    hash = sctp_assoc_hashfn(net, ntohs(local->v4.sin_port),
                 ntohs(peer->v4.sin_port));
    head = &sctp_assoc_hashtable[hash];
    read_lock(&head->lock);
    sctp_for_each_hentry(epb, node, &head->chain) {
        asoc = sctp_assoc(epb);
        transport = sctp_assoc_is_match(asoc, net, local, peer);
        if (transport)
            goto hit;
    }

    read_unlock(&head->lock);

    return NULL;

hit:
    *pt = transport;
    sctp_association_hold(asoc);
    read_unlock(&head->lock);
    return asoc;
}

/* Look up an association. BH-safe. */
SCTP_STATIC
struct sctp_association *sctp_lookup_association(struct net *net,
                         const union sctp_addr *laddr,
                         const union sctp_addr *paddr,
                        struct sctp_transport **transportp)
{
    struct sctp_association *asoc;

    sctp_local_bh_disable();
    asoc = __sctp_lookup_association(net, laddr, paddr, transportp);
    sctp_local_bh_enable();

    return asoc;
}

/* Is there an association matching the given local and peer addresses? */
int sctp_has_association(struct net *net,
             const union sctp_addr *laddr,
             const union sctp_addr *paddr)
{
    struct sctp_association *asoc;
    struct sctp_transport *transport;

    if ((asoc = sctp_lookup_association(net, laddr, paddr, &transport))) {
        sctp_association_put(asoc);
        return 1;
    }

    return 0;
}

/*
 * SCTP Implementors Guide, 2.18 Handling of address
 * parameters within the INIT or INIT-ACK.
 *
 * D) When searching for a matching TCB upon reception of an INIT
 *    or INIT-ACK chunk the receiver SHOULD use not only the
 *    source address of the packet (containing the INIT or
 *    INIT-ACK) but the receiver SHOULD also use all valid
 *    address parameters contained within the chunk.
 *
 * 2.18.3 Solution description
 *
 * This new text clearly specifies to an implementor the need
 * to look within the INIT or INIT-ACK. Any implementation that
 * does not do this, may not be able to establish associations
 * in certain circumstances.
 *
 */
static struct sctp_association *__sctp_rcv_init_lookup(struct net *net,
    struct sk_buff *skb,
    const union sctp_addr *laddr, struct sctp_transport **transportp)
{
    struct sctp_association *asoc;
    union sctp_addr addr;
    union sctp_addr *paddr = &addr;
    struct sctphdr *sh = sctp_hdr(skb);
    union sctp_params params;
    sctp_init_chunk_t *init;
    struct sctp_transport *transport;
    struct sctp_af *af;

    /*
     * This code will NOT touch anything inside the chunk--it is
     * strictly READ-ONLY.
     *
     * RFC 2960 3  SCTP packet Format
     *
     * Multiple chunks can be bundled into one SCTP packet up to
     * the MTU size, except for the INIT, INIT ACK, and SHUTDOWN
     * COMPLETE chunks.  These chunks MUST NOT be bundled with any
     * other chunk in a packet.  See Section 6.10 for more details
     * on chunk bundling.
     */

    /* Find the start of the TLVs and the end of the chunk.  This is
     * the region we search for address parameters.
     */
    init = (sctp_init_chunk_t *)skb->data;

    /* Walk the parameters looking for embedded addresses. */
    sctp_walk_params(params, init, init_hdr.params) {

        /* Note: Ignoring hostname addresses. */
        af = sctp_get_af_specific(param_type2af(params.p->type));
        if (!af)
            continue;

        af->from_addr_param(paddr, params.addr, sh->source, 0);

        asoc = __sctp_lookup_association(net, laddr, paddr, &transport);
        if (asoc)
            return asoc;
    }

    return NULL;
}

/* ADD-IP, Section 5.2
 * When an endpoint receives an ASCONF Chunk from the remote peer
 * special procedures may be needed to identify the association the
 * ASCONF Chunk is associated with. To properly find the association
 * the following procedures SHOULD be followed:
 *
 * D2) If the association is not found, use the address found in the
 * Address Parameter TLV combined with the port number found in the
 * SCTP common header. If found proceed to rule D4.
 *
 * D2-ext) If more than one ASCONF Chunks are packed together, use the
 * address found in the ASCONF Address Parameter TLV of each of the
 * subsequent ASCONF Chunks. If found, proceed to rule D4.
 */
static struct sctp_association *__sctp_rcv_asconf_lookup(
                    struct net *net,
                    sctp_chunkhdr_t *ch,
                    const union sctp_addr *laddr,
                    __be16 peer_port,
                    struct sctp_transport **transportp)
{
    sctp_addip_chunk_t *asconf = (struct sctp_addip_chunk *)ch;
    struct sctp_af *af;
    union sctp_addr_param *param;
    union sctp_addr paddr;

    /* Skip over the ADDIP header and find the Address parameter */
    param = (union sctp_addr_param *)(asconf + 1);

    af = sctp_get_af_specific(param_type2af(param->p.type));
    if (unlikely(!af))
        return NULL;

    af->from_addr_param(&paddr, param, peer_port, 0);

    return __sctp_lookup_association(net, laddr, &paddr, transportp);
}


/* SCTP-AUTH, Section 6.3:
*    If the receiver does not find a STCB for a packet containing an AUTH
*    chunk as the first chunk and not a COOKIE-ECHO chunk as the second
*    chunk, it MUST use the chunks after the AUTH chunk to look up an existing
*    association.
*
* This means that any chunks that can help us identify the association need
* to be looked at to find this association.
*/
static struct sctp_association *__sctp_rcv_walk_lookup(struct net *net,
                      struct sk_buff *skb,
                      const union sctp_addr *laddr,
                      struct sctp_transport **transportp)
{
    struct sctp_association *asoc = NULL;
    sctp_chunkhdr_t *ch;
    int have_auth = 0;
    unsigned int chunk_num = 1;
    __u8 *ch_end;

    /* Walk through the chunks looking for AUTH or ASCONF chunks
     * to help us find the association.
     */
    ch = (sctp_chunkhdr_t *) skb->data;
    do {
        /* Break out if chunk length is less then minimal. */
        if (ntohs(ch->length) < sizeof(sctp_chunkhdr_t))
            break;

        ch_end = ((__u8 *)ch) + WORD_ROUND(ntohs(ch->length));
        if (ch_end > skb_tail_pointer(skb))
            break;

        switch(ch->type) {
            case SCTP_CID_AUTH:
                have_auth = chunk_num;
                break;

            case SCTP_CID_COOKIE_ECHO:
                /* If a packet arrives containing an AUTH chunk as
                 * a first chunk, a COOKIE-ECHO chunk as the second
                 * chunk, and possibly more chunks after them, and
                 * the receiver does not have an STCB for that
                 * packet, then authentication is based on
                 * the contents of the COOKIE- ECHO chunk.
                 */
                if (have_auth == 1 && chunk_num == 2)
                    return NULL;
                break;

            case SCTP_CID_ASCONF:
                if (have_auth || net->sctp.addip_noauth)
                    asoc = __sctp_rcv_asconf_lookup(
                            net, ch, laddr,
                            sctp_hdr(skb)->source,
                            transportp);
            default:
                break;
        }

        if (asoc)
            break;

        ch = (sctp_chunkhdr_t *) ch_end;
        chunk_num++;
    } while (ch_end < skb_tail_pointer(skb));

    return asoc;
}

/*
 * There are circumstances when we need to look inside the SCTP packet
 * for information to help us find the association.   Examples
 * include looking inside of INIT/INIT-ACK chunks or after the AUTH
 * chunks.
 */
static struct sctp_association *__sctp_rcv_lookup_harder(struct net *net,
                      struct sk_buff *skb,
                      const union sctp_addr *laddr,
                      struct sctp_transport **transportp)
{
    sctp_chunkhdr_t *ch;

    ch = (sctp_chunkhdr_t *) skb->data;

    /* The code below will attempt to walk the chunk and extract
     * parameter information.  Before we do that, we need to verify
     * that the chunk length doesn't cause overflow.  Otherwise, we'll
     * walk off the end.
     */
    if (WORD_ROUND(ntohs(ch->length)) > skb->len)
        return NULL;

    /* If this is INIT/INIT-ACK look inside the chunk too. */
    switch (ch->type) {
    case SCTP_CID_INIT:
    case SCTP_CID_INIT_ACK:
        return __sctp_rcv_init_lookup(net, skb, laddr, transportp);
        break;

    default:
        return __sctp_rcv_walk_lookup(net, skb, laddr, transportp);
        break;
    }


    return NULL;
}

/* Lookup an association for an inbound skb. */
static struct sctp_association *__sctp_rcv_lookup(struct net *net,
                      struct sk_buff *skb,
                      const union sctp_addr *paddr,
                      const union sctp_addr *laddr,
                      struct sctp_transport **transportp)
{
    struct sctp_association *asoc;

    asoc = __sctp_lookup_association(net, laddr, paddr, transportp);

    /* Further lookup for INIT/INIT-ACK packets.
     * SCTP Implementors Guide, 2.18 Handling of address
     * parameters within the INIT or INIT-ACK.
     */
    if (!asoc)
        asoc = __sctp_rcv_lookup_harder(net, skb, laddr, transportp);

    return asoc;
}