: Ignore ACKs ACKs on half open connections in TCP conntrack

PATCH In review Patrick McHardy 2 participants 3 messages Dec 1, 2005

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Patrick McHardy

author

2005-12-01 11:06 UTC #0 lore raw

PATCH 1/2 : Ignore ACKs ACKs on half open connections in TCP conntrack

[NETFILTER]: Ignore ACKs ACKs on half open connections in TCP conntrack

Mounting NFS file systems after a (warm) reboot could take a long time if firewalling and connection tracking was enabled.

The reason is that the NFS clients tends to use the same ports (800 and counting down). Now on reboot, the server would still have a TCB for an existing TCP connection client:800 -> server:2049. The client sends a SYN from port 800 to server:2049, which elicits an ACK from the server. The firewall on the client drops the ACK because (from its point of view) the connection is still in half-open state, and it expects to see a SYNACK.

The client will eventually time out after several minutes.

The following patch corrects this, by accepting ACKs on half open connections as well.

Signed-off-by Jozsef Kadlecsik <[email protected]>

Signed-off-by Patrick McHardy <[email protected]>

---
commit 28fbc43b64e0982cdb775afb2055f4c02fd6c41a
tree 6013cdc2d54ae98d6b57b2b86457e496257780d3
parent 4168f7a31801bba6acc18662978d24ec850bbbd0
author Jozsef Kadlecsik <[email protected]> Tue, 29 Nov 2005 23:31:33 +0100 committer Patrick McHardy <[email protected]> Tue, 29 Nov 2005 23:31:33 +0100

 net/ipv4/netfilter/ip_conntrack_proto_tcp.c |   29 +++++++++++++++++++--------
 net/netfilter/nf_conntrack_proto_tcp.c      |   29 +++++++++++++++++++--------
 2 files changed, 40 insertions(+), 18 deletions(-)

net/ipv4/netfilter/ip_conntrack_proto_tcp.c +20 -9

index ee3b7d6..9721578 100644
@@ -272,9 +272,9 @@ static enum tcp_conntrack tcp_conntracks
  *	sCL -> sCL
  */
 /* 	     sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI	*/
-/*ack*/	   { sIV, sIV, sSR, sES, sCW, sCW, sTW, sTW, sCL, sIV },
+/*ack*/	   { sIV, sIG, sSR, sES, sCW, sCW, sTW, sTW, sCL, sIV },
 /*
- *	sSS -> sIV	Might be a half-open connection.
+ *	sSS -> sIG	Might be a half-open connection.
  *	sSR -> sSR	Might answer late resent SYN.
  *	sES -> sES	:-)
  *	sFW -> sCW	Normal close request answered by ACK.

@@ -917,8 +917,12 @@ static int tcp_packet(struct ip_conntrac
 
 	switch (new_state) {
 	case TCP_CONNTRACK_IGNORE:
-		/* Either SYN in ORIGINAL
-		 * or SYN/ACK in REPLY. */
+		/* Ignored packets:
+		 * 
+		 * a) SYN in ORIGINAL
+		 * b) SYN/ACK in REPLY
+		 * c) ACK in reply direction after initial SYN in original.
+		 */
 		if (index == TCP_SYNACK_SET
 		    && conntrack->proto.tcp.last_index == TCP_SYN_SET
 		    && conntrack->proto.tcp.last_dir != dir

@@ -985,13 +989,20 @@ static int tcp_packet(struct ip_conntrac
 		}
 	case TCP_CONNTRACK_CLOSE:
 		if (index == TCP_RST_SET
-		    && test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status)
-		    && conntrack->proto.tcp.last_index == TCP_SYN_SET
+		    && ((test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status)
+		         && conntrack->proto.tcp.last_index == TCP_SYN_SET)
+		        || (!test_bit(IPS_ASSURED_BIT, &conntrack->status)
+		            && conntrack->proto.tcp.last_index == TCP_ACK_SET))
 		    && ntohl(th->ack_seq) == conntrack->proto.tcp.last_end) {
-			/* RST sent to invalid SYN we had let trough
-			 * SYN was in window then, tear down connection.
+			/* RST sent to invalid SYN or ACK we had let trough
+			 * at a) and c) above:
+			 *
+			 * a) SYN was in window then
+			 * c) we hold a half-open connection.
+			 *
+			 * Delete our connection entry.
 			 * We skip window checking, because packet might ACK
-			 * segments we ignored in the SYN. */
+			 * segments we ignored. */
 			goto in_window;
 		}
 		/* Just fall trough */

net/netfilter/nf_conntrack_proto_tcp.c +20 -9

index 5a6fcf3..6035633 100644
@@ -280,9 +280,9 @@ static enum tcp_conntrack tcp_conntracks
  *	sCL -> sCL
  */
 /* 	     sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI	*/
-/*ack*/	   { sIV, sIV, sSR, sES, sCW, sCW, sTW, sTW, sCL, sIV },
+/*ack*/	   { sIV, sIG, sSR, sES, sCW, sCW, sTW, sTW, sCL, sIV },
 /*
- *	sSS -> sIV	Might be a half-open connection.
+ *	sSS -> sIG	Might be a half-open connection.
  *	sSR -> sSR	Might answer late resent SYN.
  *	sES -> sES	:-)
  *	sFW -> sCW	Normal close request answered by ACK.

@@ -912,8 +912,12 @@ static int tcp_packet(struct nf_conn *co
 
 	switch (new_state) {
 	case TCP_CONNTRACK_IGNORE:
-		/* Either SYN in ORIGINAL
-		 * or SYN/ACK in REPLY. */
+		/* Ignored packets:
+		 *
+		 * a) SYN in ORIGINAL
+		 * b) SYN/ACK in REPLY
+		 * c) ACK in reply direction after initial SYN in original. 
+		 */
 		if (index == TCP_SYNACK_SET
 		    && conntrack->proto.tcp.last_index == TCP_SYN_SET
 		    && conntrack->proto.tcp.last_dir != dir

@@ -979,13 +983,20 @@ static int tcp_packet(struct nf_conn *co
 		}
 	case TCP_CONNTRACK_CLOSE:
 		if (index == TCP_RST_SET
-		    && test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status)
-		    && conntrack->proto.tcp.last_index == TCP_SYN_SET
+		    && ((test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status)
+		         && conntrack->proto.tcp.last_index == TCP_SYN_SET)
+		        || (!test_bit(IPS_ASSURED_BIT, &conntrack->status)
+		            && conntrack->proto.tcp.last_index == TCP_ACK_SET))
 		    && ntohl(th->ack_seq) == conntrack->proto.tcp.last_end) {
-			/* RST sent to invalid SYN we had let trough
-			 * SYN was in window then, tear down connection.
+			/* RST sent to invalid SYN or ACK we had let trough
+			 * at a) and c) above:
+			 *
+			 * a) SYN was in window then
+			 * c) we hold a half-open connection.
+			 *
+			 * Delete our connection entry.
 			 * We skip window checking, because packet might ACK
-			 * segments we ignored in the SYN. */
+			 * segments we ignored. */
 			goto in_window;
 		}
 		/* Just fall trough */

Patrick McHardy

author

2005-12-01 11:06 UTC #1 lore raw

PATCH 2/2 : Fix recent match jiffies wrap mismatches

[NETFILTER]: Fix recent match jiffies wrap mismatches

Around jiffies wrap time (i.e. within first 5 mins after boot), recent match rules which contain both --seconds and --hitcount arguments experience false matches.

This is because the last_pkts array is filled with zeros on creation, and when comparing 'now' to 0 (+ --seconds argument), time_before_eq thinks it has found a hit.

Below patch adds a break if the packet value is zero. This has the unfortunate side effect of causing mismatches if a packet was received when jiffies really was equal to zero. The odds of that happening are slim compared to the problems caused by not adding the break however. Plus, the author used this same method just below, so it is "good enough".

This fixes netfilter bugs #383 and #395.

Signed-off-by Phil Oester <[email protected]>

Signed-off-by Patrick McHardy <[email protected]>

---
commit fb344289abd5a78a1ac7f295353d2dc4aa739bf3
tree eb5bacd9963fc9ed44ef9976bc507cffb180fb0d
parent 28fbc43b64e0982cdb775afb2055f4c02fd6c41a
author Phil Oester <[email protected]> Wed, 30 Nov 2005 00:05:21 +0100 committer Patrick McHardy <[email protected]> Wed, 30 Nov 2005 00:05:21 +0100

 net/ipv4/netfilter/ipt_recent.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

net/ipv4/netfilter/ipt_recent.c +1 -0

index 2d44b07..261cbb4 100644
@@ -532,6 +532,7 @@ match(const struct sk_buff *skb,
 			}
 			if(info->seconds && info->hit_count) {
 				for(pkt_count = 0, hits_found = 0; pkt_count < ip_pkt_list_tot; pkt_count++) {
+					if(r_list[location].last_pkts[pkt_count] == 0) break;
 					if(time_before_eq(now,r_list[location].last_pkts[pkt_count]+info->seconds*HZ)) hits_found++;
 				}
 				if(hits_found >= info->hit_count) ans = !info->invert; else ans = info->invert;

David S. Miller

maintainer

2005-12-01 22:29 UTC #2 lore raw

Re: [NETFILTER 2/2]: Fix recent match jiffies wrap mismatches

Both patches applied, thanks everyone.