[NETFILTER -stable]: nf_conntrack_tcp: conntrack reopening fix

* [NETFILTER -stable]: nf_conntrack_tcp: conntrack reopening fix
@ 2008-02-19 15:24 Patrick McHardy
  2008-02-22 21:23 ` patch netfilter-nf_conntrack_tcp-conntrack-reopening-fix.patch queued to -stable tree gregkh
                   ` (2 more replies)
  0 siblings, 3 replies; 4+ messages in thread
From: Patrick McHardy @ 2008-02-19 15:24 UTC (permalink / raw)
  To: stable; +Cc: Netfilter Development Mailinglist, David S. Miller

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This patch fixes a regression introduced by the TCP connection
reopening patch in stable-2.6.22 and upstream 2.6.23. The
patch applies to all -stable kernels since 2.6.22.

Please apply, thanks.



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commit 4df1ef24e190c5f4c069ae681a97c8c36d8c4546
Author: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Date:   Tue Feb 5 22:51:09 2008 +0100

    [NETFILTER]: nf_conntrack_tcp: conntrack reopening fix
    
    [Upstream commits b2155e7f + d0c1fd7a]
    
    TCP connection tracking in netfilter did not handle TCP reopening
    properly: active close was taken into account for one side only and
    not for any side, which is fixed now. The patch includes more comments
    to explain the logic how the different cases are handled.
    The bug was discovered by Jeff Chua.
    
    Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
    Signed-off-by: Patrick McHardy <kaber@trash.net>

diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index 7a3f64c..17ef459 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -135,7 +135,7 @@ enum tcp_bit_set {
  * CLOSE_WAIT:	ACK seen (after FIN)
  * LAST_ACK:	FIN seen (after FIN)
  * TIME_WAIT:	last ACK seen
- * CLOSE:	closed connection
+ * CLOSE:	closed connection (RST)
  *
  * LISTEN state is not used.
  *
@@ -834,8 +834,21 @@ static int tcp_packet(struct nf_conn *conntrack,
 	case TCP_CONNTRACK_SYN_SENT:
 		if (old_state < TCP_CONNTRACK_TIME_WAIT)
 			break;
-		if ((conntrack->proto.tcp.seen[!dir].flags &
-			IP_CT_TCP_FLAG_CLOSE_INIT)
+		/* RFC 1122: "When a connection is closed actively,
+		 * it MUST linger in TIME-WAIT state for a time 2xMSL
+		 * (Maximum Segment Lifetime). However, it MAY accept
+		 * a new SYN from the remote TCP to reopen the connection
+		 * directly from TIME-WAIT state, if..."
+		 * We ignore the conditions because we are in the
+		 * TIME-WAIT state anyway.
+		 *
+		 * Handle aborted connections: we and the server
+		 * think there is an existing connection but the client
+		 * aborts it and starts a new one.
+		 */
+		if (((conntrack->proto.tcp.seen[dir].flags
+		      | conntrack->proto.tcp.seen[!dir].flags)
+		     & IP_CT_TCP_FLAG_CLOSE_INIT)
 		    || (conntrack->proto.tcp.last_dir == dir
 		        && conntrack->proto.tcp.last_index == TCP_RST_SET)) {
 			/* Attempt to reopen a closed/aborted connection.
@@ -848,18 +861,25 @@ static int tcp_packet(struct nf_conn *conntrack,
 		}
 		/* Fall through */
 	case TCP_CONNTRACK_IGNORE:
-		/* Ignored packets:
+		/* Ignored packets: 
+		 *
+		 * Our connection entry may be out of sync, so ignore
+		 * packets which may signal the real connection between
+		 * the client and the server.
 		 *
 		 * a) SYN in ORIGINAL
 		 * b) SYN/ACK in REPLY
 		 * c) ACK in reply direction after initial SYN in original.
+		 *
+		 * If the ignored packet is invalid, the receiver will send 
+		 * a RST we'll catch below.
 		 */
 		if (index == TCP_SYNACK_SET
 		    && conntrack->proto.tcp.last_index == TCP_SYN_SET
 		    && conntrack->proto.tcp.last_dir != dir
 		    && ntohl(th->ack_seq) ==
 			     conntrack->proto.tcp.last_end) {
-			/* This SYN/ACK acknowledges a SYN that we earlier
+			/* b) This SYN/ACK acknowledges a SYN that we earlier
 			 * ignored as invalid. This means that the client and
 			 * the server are both in sync, while the firewall is
 			 * not. We kill this session and block the SYN/ACK so
@@ -884,7 +904,7 @@ static int tcp_packet(struct nf_conn *conntrack,
 		write_unlock_bh(&tcp_lock);
 		if (LOG_INVALID(IPPROTO_TCP))
 			nf_log_packet(pf, 0, skb, NULL, NULL, NULL,
-				  "nf_ct_tcp: invalid packed ignored ");
+				  "nf_ct_tcp: invalid packet ignored ");
 		return NF_ACCEPT;
 	case TCP_CONNTRACK_MAX:
 		/* Invalid packet */
@@ -938,8 +958,7 @@ static int tcp_packet(struct nf_conn *conntrack,
 
 	conntrack->proto.tcp.state = new_state;
 	if (old_state != new_state
-	    && (new_state == TCP_CONNTRACK_FIN_WAIT
-		|| new_state == TCP_CONNTRACK_CLOSE))
+	    && new_state == TCP_CONNTRACK_FIN_WAIT)
 		conntrack->proto.tcp.seen[dir].flags |= IP_CT_TCP_FLAG_CLOSE_INIT;
 	timeout = conntrack->proto.tcp.retrans >= nf_ct_tcp_max_retrans
 		  && *tcp_timeouts[new_state] > nf_ct_tcp_timeout_max_retrans

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