[SCTP]: Allow spillover of receive buffer to avoid deadlock.

This patch fixes a deadlock situation in the receive path by allowing
temporary spillover of the receive buffer.

- If the chunk we receive has a tsn that immediately follows the ctsn,
  accept it even if we run out of receive buffer space and renege data with
  higher TSNs.
- Once we accept one chunk in a packet, accept all the remaining chunks
  even if we run out of receive buffer space.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Mark Butler <butlerm@middle.net>
Acked-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sctp/structs.h

@@ -712,6 +712,7 @@ struct sctp_chunk {
 	__u8 tsn_gap_acked;	/* Is this chunk acked by a GAP ACK? */
 	__s8 fast_retransmit;	 /* Is this chunk fast retransmitted? */
 	__u8 tsn_missing_report; /* Data chunk missing counter. */
+	__u8 data_accepted; 	/* At least 1 chunk in this packet accepted */
 };
 
 void sctp_chunk_hold(struct sctp_chunk *);