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input.c

/* SCTP kernel reference 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 reference Implementation
 *
 * These functions handle all input from the IP layer into SCTP.
 *
 * The SCTP reference 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.
 *
 * The SCTP reference 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>

/* 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);
      __u32 cmp = ntohl(sh->checksum);
      __u32 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",  __FUNCTION__);

      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;

      *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;

      if (ntohl(sctphdr->vtag) != asoc->c.peer_vtag) {
            ICMP_INC_STATS_BH(ICMP_MIB_INERRORS);
            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(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(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(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;
      epb = &ep->base;

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;

      /* 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;

      /*
       * 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;
}

/* 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.
*
* TODO: The only chunk currently defined that can do that is ASCONF, but we
* don't support that functionality yet.
*/
static struct sctp_association *__sctp_rcv_auth_lookup(struct sk_buff *skb,
                              const union sctp_addr *paddr,
                              const union sctp_addr *laddr,
                              struct sctp_transport **transportp)
{
      /* XXX - walk through the chunks looking for something that can
       * help us find the association.  INIT, and INIT-ACK are not permitted.
       * That leaves ASCONF, but we don't support that yet.
       */
      return NULL;
}

/*
 * 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 *paddr,
                              const union sctp_addr *laddr,
                              struct sctp_transport **transportp)
{
      sctp_chunkhdr_t *ch;

      ch = (sctp_chunkhdr_t *) skb->data;

      /* 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;

      case SCTP_CID_AUTH:
            return __sctp_rcv_auth_lookup(skb, paddr, 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, paddr, laddr, transportp);

      return asoc;
}

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