[TCP]: MD5 Signature Option (RFC2385) support.

Based on implementation by Rick Payne.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 4a8c96c..6ab3423 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2677,6 +2677,14 @@
 					   opt_rx->sack_ok) {
 						TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
 					}
+#ifdef CONFIG_TCP_MD5SIG
+				case TCPOPT_MD5SIG:
+					/*
+					 * The MD5 Hash has already been
+					 * checked (see tcp_v{4,6}_do_rcv()).
+					 */
+					break;
+#endif
 	  			};
 	  			ptr+=opsize-2;
 	  			length-=opsize;