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;
}

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.