[NETFILTER]: TCP window tracking bug fixes.

1) Name IP_CT_TCP_STATE_FLAG_WINDOW_SCALE more consistently.
2) Client sends SYN, server responds with SYN/ACK.  However
   the SYN/ACK is lost in transit and the client keeps
   sending the SYNs.  The server times out, restarts, and
   sends SYN/ACK with new sequence numbers.  Those packets
   were however erroneously dropped by the window tracking code.
3) NFS client and server, client crashes and connects to the
   server from the same port as before the crash.  Server
   thinks the connection is still alove and sends an ACK,
   client responds with a RST and tears down the connection
   so that it can start a new one.  That was not handled by
   the previous code.
4) Occasionally the window tracking code logged BUG lines due
   to a leftover ack instead of sack in the logging part.
Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netfilter_ipv4/ip_conntrack_tcp.h

@@ -18,7 +18,7 @@ enum tcp_conntrack {
 };
 
 /* Window scaling is advertised by the sender */
-#define IP_CT_TCP_STATE_FLAG_WINDOW_SCALE	0x01
+#define IP_CT_TCP_FLAG_WINDOW_SCALE		0x01
 
 /* SACK is permitted by the sender */
 #define IP_CT_TCP_FLAG_SACK_PERM		0x02

net/ipv4/netfilter/ip_conntrack_proto_tcp.c

@@ -273,9 +273,9 @@ static enum tcp_conntrack tcp_conntracks[2][6][TCP_CONNTRACK_MAX] = {
  *	sCL -> sCL
  */
 /* 	     sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI	*/
-/*ack*/	   { sIV, sIV, sIV, sES, sCW, sCW, sTW, sTW, sCL, sIV },
+/*ack*/	   { sIV, sIG, sIV, sES, sCW, sCW, sTW, sTW, sCL, sIV },
 /*
- *	sSS -> sIV	ACK is invalid: we haven't seen a SYN/ACK yet.
+ *	sSS -> sIG	Might be a half-open connection.
  *	sSR -> sIV	Simultaneous open.
  *	sES -> sES	:-)
  *	sFW -> sCW	Normal close request answered by ACK.
@@ -436,7 +436,7 @@ static void tcp_options(const struct sk_buff *skb,
 					state->td_scale = 14;
 				}
 				state->flags |=
-					IP_CT_TCP_STATE_FLAG_WINDOW_SCALE;
+					IP_CT_TCP_FLAG_WINDOW_SCALE;
 			}
 			ptr += opsize - 2;
 			length -= opsize;
@@ -552,8 +552,8 @@ static int tcp_in_window(struct ip_ct_tcp *state,
 			 * Both sides must send the Window Scale option
 			 * to enable window scaling in either direction.
 			 */
-			if (!(sender->flags & IP_CT_TCP_STATE_FLAG_WINDOW_SCALE
-			      && receiver->flags & IP_CT_TCP_STATE_FLAG_WINDOW_SCALE))
+			if (!(sender->flags & IP_CT_TCP_FLAG_WINDOW_SCALE
+			      && receiver->flags & IP_CT_TCP_FLAG_WINDOW_SCALE))
 				sender->td_scale = 
 				receiver->td_scale = 0;
 		} else {
@@ -566,8 +566,10 @@ static int tcp_in_window(struct ip_ct_tcp *state,
 			sender->td_maxwin = (win == 0 ? 1 : win);
 			sender->td_maxend = end + sender->td_maxwin;
 		}
-	} else if (state->state == TCP_CONNTRACK_SYN_SENT
-		   && dir == IP_CT_DIR_ORIGINAL
+	} else if (((state->state == TCP_CONNTRACK_SYN_SENT
+		     && dir == IP_CT_DIR_ORIGINAL)
+		    || (state->state == TCP_CONNTRACK_SYN_RECV
+		        && dir == IP_CT_DIR_REPLY))
 		    && after(end, sender->td_end)) {
 		/*
 		 * RFC 793: "if a TCP is reinitialized ... then it need
@@ -685,7 +687,7 @@ static int tcp_in_window(struct ip_ct_tcp *state,
 			"ip_ct_tcp: %s ",
 			before(end, sender->td_maxend + 1) ?
 			after(seq, sender->td_end - receiver->td_maxwin - 1) ?
-			before(ack, receiver->td_end + 1) ?
+			before(sack, receiver->td_end + 1) ?
 			after(ack, receiver->td_end - MAXACKWINDOW(sender)) ? "BUG"
 			: "ACK is under the lower bound (possibly overly delayed ACK)"
 			: "ACK is over the upper bound (ACKed data has never seen yet)"
@@ -846,7 +848,9 @@ static int tcp_packet(struct ip_conntrack *conntrack,
 
 	switch (new_state) {
 	case TCP_CONNTRACK_IGNORE:
-		/* Either SYN in ORIGINAL, or SYN/ACK in REPLY direction. */
+		/* Either SYN in ORIGINAL
+		 * or SYN/ACK in REPLY
+		 * or ACK in REPLY direction (half-open connection). */
 		if (index == TCP_SYNACK_SET
 		    && conntrack->proto.tcp.last_index == TCP_SYN_SET
 		    && conntrack->proto.tcp.last_dir != dir
@@ -875,7 +879,7 @@ static int tcp_packet(struct ip_conntrack *conntrack,
 		WRITE_UNLOCK(&tcp_lock);
 		if (LOG_INVALID(IPPROTO_TCP))
 			nf_log_packet(PF_INET, 0, skb, NULL, NULL, 
-				  "ip_ct_tcp: invalid SYN (ignored) ");
+				  "ip_ct_tcp: invalid packet ignored ");
 		return NF_ACCEPT;
 	case TCP_CONNTRACK_MAX:
 		/* Invalid packet */
@@ -900,11 +904,12 @@ static int tcp_packet(struct ip_conntrack *conntrack,
 		break;
 	case TCP_CONNTRACK_CLOSE:
 		if (index == TCP_RST_SET
-		    && test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status)
-		    && conntrack->proto.tcp.last_index <= TCP_SYNACK_SET
+		    && ((test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status)
+		         && conntrack->proto.tcp.last_index <= TCP_SYNACK_SET)
+		        || conntrack->proto.tcp.last_index == TCP_ACK_SET)
 		    && after(ntohl(th->ack_seq),
 		    	     conntrack->proto.tcp.last_seq)) {
-			/* Ignore RST closing down invalid SYN 
+			/* Ignore RST closing down invalid SYN or ACK
 			   we had let trough. */ 
 		    	WRITE_UNLOCK(&tcp_lock);
 			if (LOG_INVALID(IPPROTO_TCP))