sctp: verify length provided in heartbeat information parameter

If the variable parameter length provided in the mandatory
heartbeat information parameter exceeds the calculated payload
length the packet has been corrupted. Reply with a parameter
length protocol violation message.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/sm_statefuns.c

@@ -1055,6 +1055,7 @@ sctp_disposition_t sctp_sf_beat_8_3(struct net *net,
 				    void *arg,
 				    sctp_cmd_seq_t *commands)
 {
+	sctp_paramhdr_t *param_hdr;
 	struct sctp_chunk *chunk = arg;
 	struct sctp_chunk *reply;
 	size_t paylen = 0;
@@ -1072,12 +1073,17 @@ sctp_disposition_t sctp_sf_beat_8_3(struct net *net,
 	 * Information field copied from the received HEARTBEAT chunk.
 	 */
 	chunk->subh.hb_hdr = (sctp_heartbeathdr_t *) chunk->skb->data;
+	param_hdr = (sctp_paramhdr_t *) chunk->subh.hb_hdr;
 	paylen = ntohs(chunk->chunk_hdr->length) - sizeof(sctp_chunkhdr_t);
+
+	if (ntohs(param_hdr->length) > paylen)
+		return sctp_sf_violation_paramlen(net, ep, asoc, type, arg,
+						  param_hdr, commands);
+
 	if (!pskb_pull(chunk->skb, paylen))
 		goto nomem;
 
-	reply = sctp_make_heartbeat_ack(asoc, chunk,
-					chunk->subh.hb_hdr, paylen);
+	reply = sctp_make_heartbeat_ack(asoc, chunk, param_hdr, paylen);
 	if (!reply)
 		goto nomem;