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);
}

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.