// SPDX-License-Identifier: GPL-2.0-or-later

  /* 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.
   *

   * Please send any bug reports or fixes you make to the
   * email address(es):

   *    lksctp developers <linux-sctp@vger.kernel.org>

   *

   * Written or modified by:
   *    La Monte H.P. Yarroll <piggy@acm.org>
   *    Karl Knutson <karl@athena.chicago.il.us>
   *    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>

   */
  
  #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>

  #include <linux/rhashtable.h>

  #include <net/sock_reuseport.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, struct sk_buff *skb,
  					const union sctp_addr *laddr,
  					const union sctp_addr *daddr);

  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;

  	__le32 val = sctp_compute_cksum(skb, 0);

  
  	if (val != cmp) {
  		/* CRC failure, dump it. */

  		__SCTP_INC_STATS(net, SCTP_MIB_CHECKSUMERRORS);

  		return -1;
  	}
  	return 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;

  	union sctp_addr src;
  	union sctp_addr dest;
  	int family;
  	struct sctp_af *af;

  	struct net *net = dev_net(skb->dev);

  	bool is_gso = skb_is_gso(skb) && skb_is_gso_sctp(skb);

  	if (skb->pkt_type != PACKET_HOST)

  		goto discard_it;

  	__SCTP_INC_STATS(net, SCTP_MIB_INSCTPPACKS);

  	/* If packet is too small to contain a single chunk, let's not
  	 * waste time on it anymore.
  	 */
  	if (skb->len < sizeof(struct sctphdr) + sizeof(struct sctp_chunkhdr) +
  		       skb_transport_offset(skb))

  		goto discard_it;

  	/* If the packet is fragmented and we need to do crc checking,
  	 * it's better to just linearize it otherwise crc computing
  	 * takes longer.
  	 */

  	if ((!is_gso && skb_linearize(skb)) ||

  	    !pskb_may_pull(skb, sizeof(struct sctphdr)))

  		goto discard_it;

  	/* Pull up the IP header. */

  	__skb_pull(skb, skb_transport_offset(skb));

  
  	skb->csum_valid = 0; /* Previous value not applicable */
  	if (skb_csum_unnecessary(skb))
  		__skb_decr_checksum_unnecessary(skb);

  	else if (!sctp_checksum_disable &&

  		 !is_gso &&

  		 sctp_rcv_checksum(net, skb) < 0)

  		goto discard_it;

  	skb->csum_valid = 1;

  	__skb_pull(skb, sizeof(struct sctphdr));

  	family = ipver2af(ip_hdr(skb)->version);

  	af = sctp_get_af_specific(family);
  	if (unlikely(!af))
  		goto discard_it;

  	SCTP_INPUT_CB(skb)->af = af;

  
  	/* 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, skb, &dest, &src);

  
  	/* 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 (transport) {
  			sctp_transport_put(transport);

  			asoc = NULL;

  			transport = 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(net, SCTP_MIB_OUTOFBLUES);

  			goto discard_release;
  		}
  	}

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

  	nf_reset_ct(skb);

  	if (sk_filter(sk, skb))

  		goto discard_release;

  
  	/* Create an SCTP packet structure. */

  	chunk = sctp_chunkify(skb, asoc, sk, GFP_ATOMIC);

  	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 = sctp_hdr(skb);

  
  	/* 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.
  	 */

  	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.
  		 */

  		bh_unlock_sock(sk);

  		sk = rcvr->sk;

  		bh_lock_sock(sk);

  	}

  	if (sock_owned_by_user(sk) || !sctp_newsk_ready(sk)) {

  		if (sctp_add_backlog(sk, skb)) {

  			bh_unlock_sock(sk);

  			sctp_chunk_free(chunk);
  			skb = NULL; /* sctp_chunk_free already freed the skb */
  			goto discard_release;
  		}

  		__SCTP_INC_STATS(net, SCTP_MIB_IN_PKT_BACKLOG);

  	} else {

  		__SCTP_INC_STATS(net, SCTP_MIB_IN_PKT_SOFTIRQ);

  		sctp_inq_push(&chunk->rcvr->inqueue, chunk);

  	}

  	bh_unlock_sock(sk);

  
  	/* Release the asoc/ep ref we took in the lookup calls. */

  	if (transport)
  		sctp_transport_put(transport);

  	else
  		sctp_endpoint_put(ep);

  	return 0;

  
  discard_it:

  	__SCTP_INC_STATS(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 (transport)
  		sctp_transport_put(transport);

  	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_transport *t = chunk->transport;

  	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;

  		local_bh_disable();

  		bh_lock_sock(sk);

  		if (sock_owned_by_user(sk) || !sctp_newsk_ready(sk)) {

  			if (sk_add_backlog(sk, skb, READ_ONCE(sk->sk_rcvbuf)))

  				sctp_chunk_free(chunk);
  			else
  				backloged = 1;

  		} else
  			sctp_inq_push(inqueue, chunk);

  		bh_unlock_sock(sk);

  		local_bh_enable();

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

  		if (!sctp_newsk_ready(sk)) {

  			if (!sk_add_backlog(sk, skb, READ_ONCE(sk->sk_rcvbuf)))

  				return 0;
  			sctp_chunk_free(chunk);
  		} else {
  			sctp_inq_push(inqueue, chunk);
  		}

  	}
  
  done:
  	/* Release the refs we took in sctp_add_backlog */
  	if (SCTP_EP_TYPE_ASSOCIATION == rcvr->type)

  		sctp_transport_put(t);

  	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_transport *t = chunk->transport;

  	struct sctp_ep_common *rcvr = chunk->rcvr;

  	int ret;

  	ret = sk_add_backlog(sk, skb, READ_ONCE(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_transport_hold(t);

  		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)) {

  		atomic_set(&t->mtu_info, pmtu);

  		asoc->pmtu_pending = 1;
  		t->pmtu_pending = 1;
  		return;
  	}

  	if (!(t->param_flags & SPP_PMTUD_ENABLE))
  		/* We can't allow retransmitting in such case, as the
  		 * retransmission would be sized just as before, and thus we
  		 * would get another icmp, and retransmit again.
  		 */
  		return;

  	/* Update transports view of the MTU. Return if no update was needed.
  	 * If an update wasn't needed/possible, it also doesn't make sense to
  	 * try to retransmit now.
  	 */
  	if (!sctp_transport_update_pmtu(t, pmtu))
  		return;

  	/* Update association pmtu. */
  	sctp_assoc_sync_pmtu(asoc);
  
  	/* Retransmit with the new pmtu setting. */

  	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 (sock_owned_by_user(sk) || !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)

  {

  	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_transport_hold(t);

  		}

  	} else {

  		struct net *net = sock_net(sk);

  		pr_debug("%s: unrecognized next header type "
  			 "encountered!
  ", __func__);

  		if (del_timer(&t->proto_unreach_timer))

  			sctp_transport_put(t);

  		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)
  {

  	struct sctp_init_chunk *chunkhdr, _chunkhdr;

  	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;

  	__u32 vtag = ntohl(sctphdr->vtag);

  	*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) {

  		/* chunk header + first 4 octects of init header */
  		chunkhdr = skb_header_pointer(skb, skb_transport_offset(skb) +
  					      sizeof(struct sctphdr),
  					      sizeof(struct sctp_chunkhdr) +
  					      sizeof(__be32), &_chunkhdr);
  		if (!chunkhdr ||

  		    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;
  	}

  	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(net, LINUX_MIB_LOCKDROPPEDICMPS);

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

  	sctp_transport_put(transport);

  	return NULL;
  }
  
  /* Common cleanup code for icmp/icmpv6 error handler. */

  void sctp_err_finish(struct sock *sk, struct sctp_transport *t)

  	__releases(&((__sk)->sk_lock.slock))

  {

  	bh_unlock_sock(sk);

  	sctp_transport_put(t);

  }
  
  /*
   * 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.
   *
   */

  int 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;

  	__u16 saveip, savesctp;

  	int err;

  	struct net *net = dev_net(skb->dev);

  	/* 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(net, ICMP_MIB_INERRORS);

  		return -ENOENT;

  	}
  	/* 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,

  					      SCTP_TRUNC4(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);

  		/* Fall through to out_unlock. */

  	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, transport);

  	return 0;

  }
  
  /*
   * 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)

  {

  	struct sctp_chunkhdr *ch, _ch;

  	int ch_end, offset = 0;

  
  	/* Scan through all the chunks in the packet.  */

  	do {

  		/* Make sure we have at least the header there */

  		if (offset + sizeof(_ch) > skb->len)

  			break;
  
  		ch = skb_header_pointer(skb, offset, sizeof(*ch), &_ch);

  		/* Break out if chunk length is less then minimal. */

  		if (ntohs(ch->length) < sizeof(_ch))

  			break;

  		ch_end = offset + SCTP_PAD4(ntohs(ch->length));

  		if (ch_end > skb->len)

  			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;

  		offset = ch_end;
  	} while (ch_end < skb->len);

  
  	return 0;
  
  discard:
  	return 1;
  }
  
  /* Insert endpoint into the hash table.  */

  static int __sctp_hash_endpoint(struct sctp_endpoint *ep)

  {

  	struct sock *sk = ep->base.sk;
  	struct net *net = sock_net(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];

  	if (sk->sk_reuseport) {
  		bool any = sctp_is_ep_boundall(sk);
  		struct sctp_ep_common *epb2;
  		struct list_head *list;
  		int cnt = 0, err = 1;
  
  		list_for_each(list, &ep->base.bind_addr.address_list)
  			cnt++;
  
  		sctp_for_each_hentry(epb2, &head->chain) {
  			struct sock *sk2 = epb2->sk;
  
  			if (!net_eq(sock_net(sk2), net) || sk2 == sk ||
  			    !uid_eq(sock_i_uid(sk2), sock_i_uid(sk)) ||
  			    !sk2->sk_reuseport)
  				continue;
  
  			err = sctp_bind_addrs_check(sctp_sk(sk2),
  						    sctp_sk(sk), cnt);
  			if (!err) {
  				err = reuseport_add_sock(sk, sk2, any);
  				if (err)
  					return err;
  				break;
  			} else if (err < 0) {
  				return err;
  			}
  		}
  
  		if (err) {
  			err = reuseport_alloc(sk, any);
  			if (err)
  				return err;
  		}
  	}

  	write_lock(&head->lock);

  	hlist_add_head(&epb->node, &head->chain);

  	write_unlock(&head->lock);

  	return 0;

  }
  
  /* Add an endpoint to the hash. Local BH-safe. */

  int sctp_hash_endpoint(struct sctp_endpoint *ep)

  {

  	int err;

  	local_bh_disable();

  	err = __sctp_hash_endpoint(ep);

  	local_bh_enable();

  
  	return err;

  }
  
  /* Remove endpoint from the hash table.  */
  static void __sctp_unhash_endpoint(struct sctp_endpoint *ep)
  {

  	struct sock *sk = ep->base.sk;

  	struct sctp_hashbucket *head;
  	struct sctp_ep_common *epb;
  
  	epb = &ep->base;

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

  
  	head = &sctp_ep_hashtable[epb->hashent];

  	if (rcu_access_pointer(sk->sk_reuseport_cb))
  		reuseport_detach_sock(sk);

  	write_lock(&head->lock);

  	hlist_del_init(&epb->node);

  	write_unlock(&head->lock);

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

  	local_bh_disable();

  	__sctp_unhash_endpoint(ep);

  	local_bh_enable();

  }

  static inline __u32 sctp_hashfn(const struct net *net, __be16 lport,
  				const union sctp_addr *paddr, __u32 seed)
  {
  	__u32 addr;
  
  	if (paddr->sa.sa_family == AF_INET6)
  		addr = jhash(&paddr->v6.sin6_addr, 16, seed);
  	else
  		addr = (__force __u32)paddr->v4.sin_addr.s_addr;
  
  	return  jhash_3words(addr, ((__force __u32)paddr->v4.sin_port) << 16 |
  			     (__force __u32)lport, net_hash_mix(net), seed);
  }

  /* Look up an endpoint. */

  static struct sctp_endpoint *__sctp_rcv_lookup_endpoint(
  					struct net *net, struct sk_buff *skb,
  					const union sctp_addr *laddr,
  					const union sctp_addr *paddr)

  {
  	struct sctp_hashbucket *head;
  	struct sctp_ep_common *epb;
  	struct sctp_endpoint *ep;

  	struct sock *sk;
  	__be16 lport;

  	int hash;

  	lport = laddr->v4.sin_port;
  	hash = sctp_ep_hashfn(net, ntohs(lport));

  	head = &sctp_ep_hashtable[hash];
  	read_lock(&head->lock);

  	sctp_for_each_hentry(epb, &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:

  	sk = ep->base.sk;
  	if (sk->sk_reuseport) {
  		__u32 phash = sctp_hashfn(net, lport, paddr, 0);
  
  		sk = reuseport_select_sock(sk, phash, skb,
  					   sizeof(struct sctphdr));
  		if (sk)
  			ep = sctp_sk(sk)->ep;
  	}

  	sctp_endpoint_hold(ep);

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

  /* rhashtable for transport */
  struct sctp_hash_cmp_arg {

  	const union sctp_addr	*paddr;
  	const struct net	*net;

  	__be16			lport;

  };
  
  static inline int sctp_hash_cmp(struct rhashtable_compare_arg *arg,
  				const void *ptr)
  {

  	struct sctp_transport *t = (struct sctp_transport *)ptr;

  	const struct sctp_hash_cmp_arg *x = arg->key;

  	int err = 1;

  	if (!sctp_cmp_addr_exact(&t->ipaddr, x->paddr))

  		return err;
  	if (!sctp_transport_hold(t))
  		return err;

  	if (!net_eq(t->asoc->base.net, x->net))

  		goto out;
  	if (x->lport != htons(t->asoc->base.bind_addr.port))

  		goto out;

  	err = 0;
  out:
  	sctp_transport_put(t);
  	return err;

  }

  static inline __u32 sctp_hash_obj(const void *data, u32 len, u32 seed)

  {
  	const struct sctp_transport *t = data;

  	return sctp_hashfn(t->asoc->base.net,

  			   htons(t->asoc->base.bind_addr.port),
  			   &t->ipaddr, seed);

  }

  static inline __u32 sctp_hash_key(const void *data, u32 len, u32 seed)

  {
  	const struct sctp_hash_cmp_arg *x = data;

  	return sctp_hashfn(x->net, x->lport, x->paddr, seed);

  }
  
  static const struct rhashtable_params sctp_hash_params = {
  	.head_offset		= offsetof(struct sctp_transport, node),
  	.hashfn			= sctp_hash_key,
  	.obj_hashfn		= sctp_hash_obj,
  	.obj_cmpfn		= sctp_hash_cmp,
  	.automatic_shrinking	= true,
  };
  
  int sctp_transport_hashtable_init(void)
  {

  	return rhltable_init(&sctp_transport_hashtable, &sctp_hash_params);

  }
  
  void sctp_transport_hashtable_destroy(void)
  {

  	rhltable_destroy(&sctp_transport_hashtable);

  }

  int sctp_hash_transport(struct sctp_transport *t)

  {

  	struct sctp_transport *transport;
  	struct rhlist_head *tmp, *list;

  	struct sctp_hash_cmp_arg arg;

  	int err;

  	if (t->asoc->temp)

  		return 0;

  	arg.net   = t->asoc->base.net;

  	arg.paddr = &t->ipaddr;
  	arg.lport = htons(t->asoc->base.bind_addr.port);

  	rcu_read_lock();

  	list = rhltable_lookup(&sctp_transport_hashtable, &arg,
  			       sctp_hash_params);
  
  	rhl_for_each_entry_rcu(transport, tmp, list, node)
  		if (transport->asoc->ep == t->asoc->ep) {

  			rcu_read_unlock();

  			return -EEXIST;

  		}

  	rcu_read_unlock();

  	err = rhltable_insert_key(&sctp_transport_hashtable, &arg,
  				  &t->node, sctp_hash_params);
  	if (err)
  		pr_err_once("insert transport fail, errno %d
  ", err);
  
  	return err;

  }
  
  void sctp_unhash_transport(struct sctp_transport *t)
  {

  	if (t->asoc->temp)
  		return;

  	rhltable_remove(&sctp_transport_hashtable, &t->node,
  			sctp_hash_params);

  }

  /* return a transport with holding it */

  struct sctp_transport *sctp_addrs_lookup_transport(
  				struct net *net,
  				const union sctp_addr *laddr,
  				const union sctp_addr *paddr)
  {

  	struct rhlist_head *tmp, *list;
  	struct sctp_transport *t;

  	struct sctp_hash_cmp_arg arg = {

  		.paddr = paddr,
  		.net   = net,

  		.lport = laddr->v4.sin_port,

  	};

  	list = rhltable_lookup(&sctp_transport_hashtable, &arg,
  			       sctp_hash_params);
  
  	rhl_for_each_entry_rcu(t, tmp, list, node) {
  		if (!sctp_transport_hold(t))
  			continue;
  
  		if (sctp_bind_addr_match(&t->asoc->base.bind_addr,
  					 laddr, sctp_sk(t->asoc->base.sk)))
  			return t;
  		sctp_transport_put(t);
  	}
  
  	return NULL;

  }

  /* return a transport without holding it, as it's only used under sock lock */

  struct sctp_transport *sctp_epaddr_lookup_transport(
  				const struct sctp_endpoint *ep,
  				const union sctp_addr *paddr)
  {

  	struct rhlist_head *tmp, *list;
  	struct sctp_transport *t;

  	struct sctp_hash_cmp_arg arg = {

  		.paddr = paddr,

  		.net   = ep->base.net,

  		.lport = htons(ep->base.bind_addr.port),

  	};

  	list = rhltable_lookup(&sctp_transport_hashtable, &arg,
  			       sctp_hash_params);
  
  	rhl_for_each_entry_rcu(t, tmp, list, node)
  		if (ep == t->asoc->ep)
  			return t;
  
  	return NULL;

  }

  /* 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_transport *t;

  	struct sctp_association *asoc = NULL;

  	t = sctp_addrs_lookup_transport(net, local, peer);

  	if (!t)

  		goto out;

  	asoc = t->asoc;

  	*pt = t;

  out:

  	return asoc;

  }

  /* Look up an association. protected by RCU read lock */

  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;

  	rcu_read_lock();

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

  	rcu_read_unlock();

  
  	return asoc;
  }
  
  /* Is there an association matching the given local and peer addresses? */

  bool sctp_has_association(struct net *net,
  			  const union sctp_addr *laddr,
  			  const union sctp_addr *paddr)

  {

  	struct sctp_transport *transport;

  	if (sctp_lookup_association(net, laddr, paddr, &transport)) {

  		sctp_transport_put(transport);

  		return true;

  	}

  	return false;

  }
  
  /*
   * 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;

  	struct sctp_init_chunk *init;

  	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 = (struct sctp_init_chunk *)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, transportp);

  		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,

  					struct sctp_chunkhdr *ch,

  					const union sctp_addr *laddr,

  					__be16 peer_port,

  					struct sctp_transport **transportp)
  {

  	struct sctp_addip_chunk *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;

  	struct sctp_chunkhdr *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 = (struct sctp_chunkhdr *)skb->data;

  	do {
  		/* Break out if chunk length is less then minimal. */

  		if (ntohs(ch->length) < sizeof(*ch))

  			break;

  		ch_end = ((__u8 *)ch) + SCTP_PAD4(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 = (struct sctp_chunkhdr *)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)
  {

  	struct sctp_chunkhdr *ch;

  	/* We do not allow GSO frames here as we need to linearize and
  	 * then cannot guarantee frame boundaries. This shouldn't be an
  	 * issue as packets hitting this are mostly INIT or INIT-ACK and
  	 * those cannot be on GSO-style anyway.
  	 */

  	if (skb_is_gso(skb) && skb_is_gso_sctp(skb))

  		return NULL;

  	ch = (struct sctp_chunkhdr *)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 (SCTP_PAD4(ntohs(ch->length)) > skb->len)

  		return NULL;

  	/* If this is INIT/INIT-ACK look inside the chunk too. */

  	if (ch->type == SCTP_CID_INIT || ch->type == SCTP_CID_INIT_ACK)

  		return __sctp_rcv_init_lookup(net, skb, laddr, transportp);

  	return __sctp_rcv_walk_lookup(net, skb, laddr, transportp);

  }

  /* 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);

  	if (asoc)
  		goto out;

  
  	/* Further lookup for INIT/INIT-ACK packets.
  	 * SCTP Implementors Guide, 2.18 Handling of address
  	 * parameters within the INIT or INIT-ACK.
  	 */

  	asoc = __sctp_rcv_lookup_harder(net, skb, laddr, transportp);
  	if (asoc)
  		goto out;

  	if (paddr->sa.sa_family == AF_INET)
  		pr_debug("sctp: asoc not found for src:%pI4:%d dst:%pI4:%d
  ",
  			 &laddr->v4.sin_addr, ntohs(laddr->v4.sin_port),
  			 &paddr->v4.sin_addr, ntohs(paddr->v4.sin_port));
  	else
  		pr_debug("sctp: asoc not found for src:%pI6:%d dst:%pI6:%d
  ",
  			 &laddr->v6.sin6_addr, ntohs(laddr->v6.sin6_port),
  			 &paddr->v6.sin6_addr, ntohs(paddr->v6.sin6_port));
  
  out:

  	return asoc;
  }