netfilter: netns nf_conntrack: per-netns net.netfilter.nf_conntrack_checksum sysctl

[linux-2.6] / net / sctp / input.c

/* 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 <lksctp-developers@lists.sourceforge.net>
 *
 * Or submit a bug report through the following website:
 *    http://www.sf.net/projects/lksctp
 *
 * Written or modified by:
 *    La Monte H.P. Yarroll <piggy@acm.org>
 *    Karl Knutson <karl@athena.chicago.il.us>
 *    Xingang Guo <xingang.guo@intel.com>
 *    Jon Grimm <jgrimm@us.ibm.com>
 *    Hui Huang <hui.huang@nokia.com>
 *    Daisy Chang <daisyc@us.ibm.com>
 *    Sridhar Samudrala <sri@us.ibm.com>
 *    Ardelle Fan <ardelle.fan@intel.com>
 *
 * 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 <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 sk_buff *skb,
                                      const union sctp_addr *laddr,
                                      const union sctp_addr *paddr,
                                      struct sctp_transport **transportp);
static struct sctp_endpoint *__sctp_rcv_lookup_endpoint(const union sctp_addr *laddr);
static struct sctp_association *__sctp_lookup_association(
                                        const union sctp_addr *local,
                                        const union sctp_addr *peer,
                                        struct sctp_transport **pt);

static void 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 sk_buff *skb)
{
        struct sk_buff *list = skb_shinfo(skb)->frag_list;
        struct sctphdr *sh = sctp_hdr(skb);
        __be32 cmp = sh->checksum;
        __be32 val = sctp_start_cksum((__u8 *)sh, skb_headlen(skb));

        for (; list; list = list->next)
                val = sctp_update_cksum((__u8 *)list->data, skb_headlen(list),
                                        val);

        val = sctp_end_cksum(val);

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

struct sctp_input_cb {
        union {
                struct inet_skb_parm    h4;
#if defined(CONFIG_IPV6) || defined (CONFIG_IPV6_MODULE)
                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;

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

        SCTP_INC_STATS_BH(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 (!skb_csum_unnecessary(skb) && sctp_rcv_checksum(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(skb, &src, &dest, &transport);

        if (!asoc)
                ep = __sctp_rcv_lookup_endpoint(&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 = sctp_get_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(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 (sock_owned_by_user(sk)) {
                SCTP_INC_STATS_BH(SCTP_MIB_IN_PKT_BACKLOG);
                sctp_add_backlog(sk, skb);
        } else {
                SCTP_INC_STATS_BH(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(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)) {
                        sk_add_backlog(sk, skb);
                        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 void 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;

        /* 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();

        sk_add_backlog(sk, skb);
}

/* 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(t, pmtu);

                /* Update association pmtu. */
                sctp_assoc_sync_pmtu(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);
}

/*
 * 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__);

        sctp_do_sm(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(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(&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 = (struct sctp_init_chunk *)((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(&init_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)
{
        struct iphdr *iph = (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;

        if (skb->len < ihlen + 8) {
                ICMP_INC_STATS_BH(&init_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(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(&init_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;
        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;
        sctp_errhdr_t *err;

        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;

                /* RFC 8.4, 7) If the packet contains a "Stale cookie" ERROR
                 * or a COOKIE ACK the SCTP Packet should be silently
                 * discarded.
                 */
                if (SCTP_CID_COOKIE_ACK == ch->type)
                        goto discard;

                if (SCTP_CID_ERROR == ch->type) {
                        sctp_walk_errors(err, ch) {
                                if (SCTP_ERROR_STALE_COOKIE == err->cause)
                                        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 sctp_ep_common *epb;
        struct sctp_hashbucket *head;

        epb = &ep->base;

        epb->hashent = sctp_ep_hashfn(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 sctp_hashbucket *head;
        struct sctp_ep_common *epb;

        epb = &ep->base;

        if (hlist_unhashed(&epb->node))
                return;

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

        head = &sctp_ep_hashtable[epb->hashent];

        sctp_write_lock(&head->lock);
        __hlist_del(&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(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(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, laddr))
                        goto hit;
        }

        ep = sctp_sk((sctp_get_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 sctp_ep_common *epb;
        struct sctp_hashbucket *head;

        epb = &asoc->base;

        /* Calculate which chain this entry will belong to. */
        epb->hashent = sctp_assoc_hashfn(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 sctp_hashbucket *head;
        struct sctp_ep_common *epb;

        epb = &asoc->base;

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

        head = &sctp_assoc_hashtable[epb->hashent];

        sctp_write_lock(&head->lock);
        __hlist_del(&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(
                                        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(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, 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(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(laddr, paddr, transportp);
        sctp_local_bh_enable();

        return asoc;
}

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

        if ((asoc = sctp_lookup_association(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 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);
        sctp_chunkhdr_t *ch;
        union sctp_params params;
        sctp_init_chunk_t *init;
        struct sctp_transport *transport;
        struct sctp_af *af;

        ch = (sctp_chunkhdr_t *) skb->data;

        /*
         * 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(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(
                                        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->v4.param_hdr.type));
        if (unlikely(!af))
                return NULL;

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

        return __sctp_lookup_association(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 assocation.
*/
static struct sctp_association *__sctp_rcv_walk_lookup(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 || sctp_addip_noauth)
                                    asoc = __sctp_rcv_asconf_lookup(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 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(skb, laddr, transportp);
                break;

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


        return NULL;
}

/* Lookup an association for an inbound skb. */
static struct sctp_association *__sctp_rcv_lookup(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(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(skb, laddr, transportp);

        return asoc;
}