[NETFILTER]: TCP conntrack: improve dead connection detection

Don't count window updates as retransmissions.
Signed-off-by: NGeorge Hansper <georgeh@anstat.com.au>
Signed-off-by: NPatrick McHardy <kaber@trash.net>

include/linux/netfilter/nf_conntrack_tcp.h

@@ -49,6 +49,7 @@ struct ip_ct_tcp
 	u_int32_t	last_seq;	/* Last sequence number seen in dir */
 	u_int32_t	last_ack;	/* Last sequence number seen in opposite dir */
 	u_int32_t	last_end;	/* Last seq + len */
+	u_int16_t	last_win;	/* Last window advertisement seen in dir */
 };
 
 #endif /* __KERNEL__ */

net/ipv4/netfilter/ip_conntrack_proto_tcp.c

@@ -731,13 +731,15 @@ static int tcp_in_window(struct ip_ct_tcp *state,
 			if (state->last_dir == dir
 			    && state->last_seq == seq
 			    && state->last_ack == ack
-			    && state->last_end == end)
+			    && state->last_end == end
+			    && state->last_win == win)
 				state->retrans++;
 			else {
 				state->last_dir = dir;
 				state->last_seq = seq;
 				state->last_ack = ack;
 				state->last_end = end;
+				state->last_win = win;
 				state->retrans = 0;
 			}
 		}

net/netfilter/nf_conntrack_proto_tcp.c

@@ -688,13 +688,15 @@ static int tcp_in_window(struct ip_ct_tcp *state,
 			if (state->last_dir == dir
 			    && state->last_seq == seq
 			    && state->last_ack == ack
-			    && state->last_end == end)
+			    && state->last_end == end
+			    && state->last_win == win)
 				state->retrans++;
 			else {
 				state->last_dir = dir;
 				state->last_seq = seq;
 				state->last_ack = ack;
 				state->last_end = end;
+				state->last_win = win;
 				state->retrans = 0;
 			}
 		}