static int sctp_sendmsg(struct sock *sk, struct msghdr *msg, size_t msg_len)
{
	struct net *net = sock_net(sk);
	struct sctp_sock *sp;
	struct sctp_endpoint *ep;
	struct sctp_association *new_asoc = NULL, *asoc = NULL;
	struct sctp_transport *transport, *chunk_tp;
	struct sctp_chunk *chunk;
	union sctp_addr to;
	struct sockaddr *msg_name = NULL;
	struct sctp_sndrcvinfo default_sinfo;
	struct sctp_sndrcvinfo *sinfo;
	struct sctp_initmsg *sinit;
	sctp_assoc_t associd = 0;
	sctp_cmsgs_t cmsgs = { NULL };
	sctp_scope_t scope;
	bool fill_sinfo_ttl = false, wait_connect = false;
	struct sctp_datamsg *datamsg;
	int msg_flags = msg->msg_flags;
	__u16 sinfo_flags = 0;
	long timeo;
	int err;

	err = 0;
	sp = sctp_sk(sk);
	ep = sp->ep;

	pr_debug("%s: sk:%p, msg:%p, msg_len:%zu ep:%p\n", __func__, sk,
		 msg, msg_len, ep);

	/* We cannot send a message over a TCP-style listening socket. */
	if (sctp_style(sk, TCP) && sctp_sstate(sk, LISTENING)) {
		err = -EPIPE;
		goto out_nounlock;
	}

	/* Parse out the SCTP CMSGs.  */
	err = sctp_msghdr_parse(msg, &cmsgs);
	if (err) {
		pr_debug("%s: msghdr parse err:%x\n", __func__, err);
		goto out_nounlock;
	}

	/* Fetch the destination address for this packet.  This
	 * address only selects the association--it is not necessarily
	 * the address we will send to.
	 * For a peeled-off socket, msg_name is ignored.
	 */
	if (!sctp_style(sk, UDP_HIGH_BANDWIDTH) && msg->msg_name) {
		int msg_namelen = msg->msg_namelen;

		err = sctp_verify_addr(sk, (union sctp_addr *)msg->msg_name,
				       msg_namelen);
		if (err)
			return err;

		if (msg_namelen > sizeof(to))
			msg_namelen = sizeof(to);
		memcpy(&to, msg->msg_name, msg_namelen);
		msg_name = msg->msg_name;
	}

	sinit = cmsgs.init;
	if (cmsgs.sinfo != NULL) {
		memset(&default_sinfo, 0, sizeof(default_sinfo));
		default_sinfo.sinfo_stream = cmsgs.sinfo->snd_sid;
		default_sinfo.sinfo_flags = cmsgs.sinfo->snd_flags;
		default_sinfo.sinfo_ppid = cmsgs.sinfo->snd_ppid;
		default_sinfo.sinfo_context = cmsgs.sinfo->snd_context;
		default_sinfo.sinfo_assoc_id = cmsgs.sinfo->snd_assoc_id;

		sinfo = &default_sinfo;
		fill_sinfo_ttl = true;
	} else {
		sinfo = cmsgs.srinfo;
	}
	/* Did the user specify SNDINFO/SNDRCVINFO? */
	if (sinfo) {
		sinfo_flags = sinfo->sinfo_flags;
		associd = sinfo->sinfo_assoc_id;
	}

	pr_debug("%s: msg_len:%zu, sinfo_flags:0x%x\n", __func__,
		 msg_len, sinfo_flags);

	/* SCTP_EOF or SCTP_ABORT cannot be set on a TCP-style socket. */
	if (sctp_style(sk, TCP) && (sinfo_flags & (SCTP_EOF | SCTP_ABORT))) {
		err = -EINVAL;
		goto out_nounlock;
	}

	/* If SCTP_EOF is set, no data can be sent. Disallow sending zero
	 * length messages when SCTP_EOF|SCTP_ABORT is not set.
	 * If SCTP_ABORT is set, the message length could be non zero with
	 * the msg_iov set to the user abort reason.
	 */
	if (((sinfo_flags & SCTP_EOF) && (msg_len > 0)) ||
	    (!(sinfo_flags & (SCTP_EOF|SCTP_ABORT)) && (msg_len == 0))) {
		err = -EINVAL;
		goto out_nounlock;
	}

	/* If SCTP_ADDR_OVER is set, there must be an address
	 * specified in msg_name.
	 */
	if ((sinfo_flags & SCTP_ADDR_OVER) && (!msg->msg_name)) {
		err = -EINVAL;
		goto out_nounlock;
	}

	transport = NULL;

	pr_debug("%s: about to look up association\n", __func__);

	lock_sock(sk);

	/* If a msg_name has been specified, assume this is to be used.  */
	if (msg_name) {
		/* Look for a matching association on the endpoint. */
		asoc = sctp_endpoint_lookup_assoc(ep, &to, &transport);

		/* If we could not find a matching association on the
		 * endpoint, make sure that it is not a TCP-style
		 * socket that already has an association or there is
		 * no peeled-off association on another socket.
		 */
		if (!asoc &&
		    ((sctp_style(sk, TCP) &&
		      (sctp_sstate(sk, ESTABLISHED) ||
		       sctp_sstate(sk, CLOSING))) ||
		     sctp_endpoint_is_peeled_off(ep, &to))) {
			err = -EADDRNOTAVAIL;
			goto out_unlock;
		}
	} else {
		asoc = sctp_id2assoc(sk, associd);
		if (!asoc) {
			err = -EPIPE;
			goto out_unlock;
		}
	}

	if (asoc) {
		pr_debug("%s: just looked up association:%p\n", __func__, asoc);

		/* We cannot send a message on a TCP-style SCTP_SS_ESTABLISHED
		 * socket that has an association in CLOSED state. This can
		 * happen when an accepted socket has an association that is
		 * already CLOSED.
		 */
		if (sctp_state(asoc, CLOSED) && sctp_style(sk, TCP)) {
			err = -EPIPE;
			goto out_unlock;
		}

		if (sinfo_flags & SCTP_EOF) {
			pr_debug("%s: shutting down association:%p\n",
				 __func__, asoc);

			sctp_primitive_SHUTDOWN(net, asoc, NULL);
			err = 0;
			goto out_unlock;
		}
		if (sinfo_flags & SCTP_ABORT) {

			chunk = sctp_make_abort_user(asoc, msg, msg_len);
			if (!chunk) {
				err = -ENOMEM;
				goto out_unlock;
			}

			pr_debug("%s: aborting association:%p\n",
				 __func__, asoc);

			sctp_primitive_ABORT(net, asoc, chunk);
			err = 0;
			goto out_unlock;
		}
	}

	/* Do we need to create the association?  */
	if (!asoc) {
		pr_debug("%s: there is no association yet\n", __func__);

		if (sinfo_flags & (SCTP_EOF | SCTP_ABORT)) {
			err = -EINVAL;
			goto out_unlock;
		}

		/* Check for invalid stream against the stream counts,
		 * either the default or the user specified stream counts.
		 */
		if (sinfo) {
			if (!sinit || !sinit->sinit_num_ostreams) {
				/* Check against the defaults. */
				if (sinfo->sinfo_stream >=
				    sp->initmsg.sinit_num_ostreams) {
					err = -EINVAL;
					goto out_unlock;
				}
			} else {
				/* Check against the requested.  */
				if (sinfo->sinfo_stream >=
				    sinit->sinit_num_ostreams) {
					err = -EINVAL;
					goto out_unlock;
				}
			}
		}

		/*
		 * API 3.1.2 bind() - UDP Style Syntax
		 * If a bind() or sctp_bindx() is not called prior to a
		 * sendmsg() call that initiates a new association, the
		 * system picks an ephemeral port and will choose an address
		 * set equivalent to binding with a wildcard address.
		 */
		if (!ep->base.bind_addr.port) {
			if (sctp_autobind(sk)) {
				err = -EAGAIN;
				goto out_unlock;
			}
		} else {
			/*
			 * If an unprivileged user inherits a one-to-many
			 * style socket with open associations on a privileged
			 * port, it MAY be permitted to accept new associations,
			 * but it SHOULD NOT be permitted to open new
			 * associations.
			 */
			if (ep->base.bind_addr.port < PROT_SOCK &&
			    !ns_capable(net->user_ns, CAP_NET_BIND_SERVICE)) {
				err = -EACCES;
				goto out_unlock;
			}
		}

		scope = sctp_scope(&to);
		new_asoc = sctp_association_new(ep, sk, scope, GFP_KERNEL);
		if (!new_asoc) {
			err = -ENOMEM;
			goto out_unlock;
		}
		asoc = new_asoc;
		err = sctp_assoc_set_bind_addr_from_ep(asoc, scope, GFP_KERNEL);
		if (err < 0) {
			err = -ENOMEM;
			goto out_free;
		}

		/* If the SCTP_INIT ancillary data is specified, set all
		 * the association init values accordingly.
		 */
		if (sinit) {
			if (sinit->sinit_num_ostreams) {
				asoc->c.sinit_num_ostreams =
					sinit->sinit_num_ostreams;
			}
			if (sinit->sinit_max_instreams) {
				asoc->c.sinit_max_instreams =
					sinit->sinit_max_instreams;
			}
			if (sinit->sinit_max_attempts) {
				asoc->max_init_attempts
					= sinit->sinit_max_attempts;
			}
			if (sinit->sinit_max_init_timeo) {
				asoc->max_init_timeo =
				 msecs_to_jiffies(sinit->sinit_max_init_timeo);
			}
		}

		/* Prime the peer's transport structures.  */
		transport = sctp_assoc_add_peer(asoc, &to, GFP_KERNEL, SCTP_UNKNOWN);
		if (!transport) {
			err = -ENOMEM;
			goto out_free;
		}
	}

	/* ASSERT: we have a valid association at this point.  */
	pr_debug("%s: we have a valid association\n", __func__);

	if (!sinfo) {
		/* If the user didn't specify SNDINFO/SNDRCVINFO, make up
		 * one with some defaults.
		 */
		memset(&default_sinfo, 0, sizeof(default_sinfo));
		default_sinfo.sinfo_stream = asoc->default_stream;
		default_sinfo.sinfo_flags = asoc->default_flags;
		default_sinfo.sinfo_ppid = asoc->default_ppid;
		default_sinfo.sinfo_context = asoc->default_context;
		default_sinfo.sinfo_timetolive = asoc->default_timetolive;
		default_sinfo.sinfo_assoc_id = sctp_assoc2id(asoc);

		sinfo = &default_sinfo;
	} else if (fill_sinfo_ttl) {
		/* In case SNDINFO was specified, we still need to fill
		 * it with a default ttl from the assoc here.
		 */
		sinfo->sinfo_timetolive = asoc->default_timetolive;
	}

	/* API 7.1.7, the sndbuf size per association bounds the
	 * maximum size of data that can be sent in a single send call.
	 */
	if (msg_len > sk->sk_sndbuf) {
		err = -EMSGSIZE;
		goto out_free;
	}

	if (asoc->pmtu_pending)
		sctp_assoc_pending_pmtu(sk, asoc);

	/* If fragmentation is disabled and the message length exceeds the
	 * association fragmentation point, return EMSGSIZE.  The I-D
	 * does not specify what this error is, but this looks like
	 * a great fit.
	 */
	if (sctp_sk(sk)->disable_fragments && (msg_len > asoc->frag_point)) {
		err = -EMSGSIZE;
		goto out_free;
	}

	/* Check for invalid stream. */
	if (sinfo->sinfo_stream >= asoc->c.sinit_num_ostreams) {
		err = -EINVAL;
		goto out_free;
	}

	if (sctp_wspace(asoc) < msg_len)
		sctp_prsctp_prune(asoc, sinfo, msg_len - sctp_wspace(asoc));

	timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
	if (!sctp_wspace(asoc)) {
		err = sctp_wait_for_sndbuf(asoc, &timeo, msg_len);
		if (err)
			goto out_free;
	}

	/* If an address is passed with the sendto/sendmsg call, it is used
	 * to override the primary destination address in the TCP model, or
	 * when SCTP_ADDR_OVER flag is set in the UDP model.
	 */
	if ((sctp_style(sk, TCP) && msg_name) ||
	    (sinfo_flags & SCTP_ADDR_OVER)) {
		chunk_tp = sctp_assoc_lookup_paddr(asoc, &to);
		if (!chunk_tp) {
			err = -EINVAL;
			goto out_free;
		}
	} else
		chunk_tp = NULL;

	/* Auto-connect, if we aren't connected already. */
	if (sctp_state(asoc, CLOSED)) {
		err = sctp_primitive_ASSOCIATE(net, asoc, NULL);
		if (err < 0)
			goto out_free;

		wait_connect = true;
		pr_debug("%s: we associated primitively\n", __func__);
	}

	/* Break the message into multiple chunks of maximum size. */
	datamsg = sctp_datamsg_from_user(asoc, sinfo, &msg->msg_iter);
	if (IS_ERR(datamsg)) {
		err = PTR_ERR(datamsg);
		goto out_free;
	}

	/* Now send the (possibly) fragmented message. */
	list_for_each_entry(chunk, &datamsg->chunks, frag_list) {
		sctp_chunk_hold(chunk);

		/* Do accounting for the write space.  */
		sctp_set_owner_w(chunk);

		chunk->transport = chunk_tp;
	}

	/* Send it to the lower layers.  Note:  all chunks
	 * must either fail or succeed.   The lower layer
	 * works that way today.  Keep it that way or this
	 * breaks.
	 */
	err = sctp_primitive_SEND(net, asoc, datamsg);
	/* Did the lower layer accept the chunk? */
	if (err) {
		sctp_datamsg_free(datamsg);
		goto out_free;
	}

	pr_debug("%s: we sent primitively\n", __func__);

	sctp_datamsg_put(datamsg);
	err = msg_len;

	if (unlikely(wait_connect)) {
		timeo = sock_sndtimeo(sk, msg_flags & MSG_DONTWAIT);
		sctp_wait_for_connect(asoc, &timeo);
	}

	/* If we are already past ASSOCIATE, the lower
	 * layers are responsible for association cleanup.
	 */
	goto out_unlock;

out_free:
	if (new_asoc)
		sctp_association_free(asoc);
out_unlock:
	release_sock(sk);

out_nounlock:
	return sctp_error(sk, msg_flags, err);

#if 0
do_sock_err:
	if (msg_len)
		err = msg_len;
	else
		err = sock_error(sk);
	goto out;

do_interrupted:
	if (msg_len)
		err = msg_len;
	goto out;
#endif /* 0 */
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.