sctp: fix association hangs due to reneging packets below the cumulative TSN ACK point

In sctp_ulpq_renege_list(), do not renege packets below the
cumulative TSN ACK point.
Signed-off-by: Lee A. Roberts <lee.roberts@hp.com>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>

net/sctp/ulpqueue.c

@@ -969,11 +969,16 @@ static __u16 sctp_ulpq_renege_list(struct sctp_ulpq *ulpq,
 
 	tsnmap = &ulpq->asoc->peer.tsn_map;
 
-	while ((skb = __skb_dequeue_tail(list)) != NULL) {
-		freed += skb_headlen(skb);
+	while ((skb = skb_peek_tail(list)) != NULL) {
 		event = sctp_skb2event(skb);
 		tsn = event->tsn;
 
+		/* Don't renege below the Cumulative TSN ACK Point. */
+		if (TSN_lte(tsn, sctp_tsnmap_get_ctsn(tsnmap)))
+			break;
+
+		__skb_unlink(skb, list);
+		freed += skb_headlen(skb);
 		sctp_ulpevent_free(event);
 		sctp_tsnmap_renege(tsnmap, tsn);
 		if (freed >= needed)