[SCTP]: Fix panic's when receiving fragmented SCTP control chunks.

Use pskb_pull() to handle incoming COOKIE_ECHO and HEARTBEAT chunks that
are received as skb's with fragment list.
Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/sm_statefuns.c

@@ -636,8 +636,9 @@ sctp_disposition_t sctp_sf_do_5_1D_ce(const struct sctp_endpoint *ep,
 	 */
         chunk->subh.cookie_hdr =
 		(struct sctp_signed_cookie *)chunk->skb->data;
-	skb_pull(chunk->skb,
-		 ntohs(chunk->chunk_hdr->length) - sizeof(sctp_chunkhdr_t));
+	if (!pskb_pull(chunk->skb, ntohs(chunk->chunk_hdr->length) -
+					 sizeof(sctp_chunkhdr_t)))
+		goto nomem;
 
 	/* 5.1 D) Upon reception of the COOKIE ECHO chunk, Endpoint
 	 * "Z" will reply with a COOKIE ACK chunk after building a TCB
@@ -965,7 +966,8 @@ sctp_disposition_t sctp_sf_beat_8_3(const struct sctp_endpoint *ep,
 	 */
 	chunk->subh.hb_hdr = (sctp_heartbeathdr_t *) chunk->skb->data;
 	paylen = ntohs(chunk->chunk_hdr->length) - sizeof(sctp_chunkhdr_t);
-	skb_pull(chunk->skb, paylen);
+	if (!pskb_pull(chunk->skb, paylen))
+		goto nomem;
 
 	reply = sctp_make_heartbeat_ack(asoc, chunk,
 					chunk->subh.hb_hdr, paylen);
@@ -1860,8 +1862,9 @@ sctp_disposition_t sctp_sf_do_5_2_4_dupcook(const struct sctp_endpoint *ep,
 	 * are in good shape.
 	 */
         chunk->subh.cookie_hdr = (struct sctp_signed_cookie *)chunk->skb->data;
-	skb_pull(chunk->skb, ntohs(chunk->chunk_hdr->length) -
-		 sizeof(sctp_chunkhdr_t));
+	if (!pskb_pull(chunk->skb, ntohs(chunk->chunk_hdr->length) -
+					sizeof(sctp_chunkhdr_t)))
+		goto nomem;
 
 	/* In RFC 2960 5.2.4 3, if both Verification Tags in the State Cookie
 	 * of a duplicate COOKIE ECHO match the Verification Tags of the