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netfilter 01/02: nf_nat: fix NAT issue in 2.6.30.4+

PATCH Applied Patrick McHardy 2 participants 2 messages Nov 5, 2009 – Nov 6, 2009

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Patrick McHardy

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Hi Dave,

the following two patches fix two netfilter bugs:

- incorrect sequence number tracking in TCP conntrack in combination with NAT helpers that enlarge the packet, causing incorrectly detected out of window packets

- a regression in the connlimit match

The first patch is quite large for this late in the release cycle, so if you prefer, I'll queue it up for net-next instead.

I'll pass on both to -stable once they hit upstream.

Please apply, thanks!

commit 0132f9835c1c19a369954e1eb56dca80a1382369

Author: Jozsef Kadlecsik <[email protected]>
Date:   Thu Sep 17 13:05:15 2009 +0200

netfilter: nf_nat: fix NAT issue in 2.6.30.4+

Vitezslav Samel discovered that since 2.6.30.4+ active FTP can not work over NAT. The "cause" of the problem was a fix of unacknowledged data detection with NAT (commit a3a9f79e361e864f0e9d75ebe2a0cb43d17c4272). However, actually, that fix uncovered a long standing bug in TCP conntrack:
when NAT was enabled, we simply updated the max of the right edge of the segments we have seen (td_end), by the offset NAT produced with changing IP/port in the data. However, we did not update the other parameter (td_maxend) which is affected by the NAT offset. Thus that could drift away from the correct value and thus resulted breaking active FTP.

The patch below fixes the issue by *not* updating the conntrack parameters from NAT, but instead taking into account the NAT offsets in conntrack in a consistent way. (Updating from NAT would be more harder and expensive because it'd need to re-calculate parameters we already calculated in conntrack.)

Signed-off-by Jozsef Kadlecsik <[email protected]>
Signed-off-by Patrick McHardy <[email protected]>
include/net/netfilter/nf_conntrack.h +3 -5
index cbdd628..5cf7270 100644
@@ -255,11 +255,9 @@ static inline bool nf_ct_kill(struct nf_conn *ct)
 }
 
 /* These are for NAT.  Icky. */
-/* Update TCP window tracking data when NAT mangles the packet */
-extern void nf_conntrack_tcp_update(const struct sk_buff *skb,
-				    unsigned int dataoff,
-				    struct nf_conn *ct, int dir,
-				    s16 offset);
+extern s16 (*nf_ct_nat_offset)(const struct nf_conn *ct,
+			       enum ip_conntrack_dir dir,
+			       u32 seq);
 
 /* Fake conntrack entry for untracked connections */
 extern struct nf_conn nf_conntrack_untracked;
include/net/netfilter/nf_nat_helper.h +4 -0
index 237a961..4222220 100644
@@ -32,4 +32,8 @@ extern int (*nf_nat_seq_adjust_hook)(struct sk_buff *skb,
  * to port ct->master->saved_proto. */
 extern void nf_nat_follow_master(struct nf_conn *ct,
 				 struct nf_conntrack_expect *this);
+
+extern s16 nf_nat_get_offset(const struct nf_conn *ct,
+			     enum ip_conntrack_dir dir,
+			     u32 seq);
 #endif
net/ipv4/netfilter/nf_nat_core.c +3 -0
index 68afc6e..fe1a644 100644
@@ -750,6 +750,8 @@ static int __init nf_nat_init(void)
 	BUG_ON(nfnetlink_parse_nat_setup_hook != NULL);
 	rcu_assign_pointer(nfnetlink_parse_nat_setup_hook,
 			   nfnetlink_parse_nat_setup);
+	BUG_ON(nf_ct_nat_offset != NULL);
+	rcu_assign_pointer(nf_ct_nat_offset, nf_nat_get_offset);
 	return 0;
 
  cleanup_extend:

@@ -764,6 +766,7 @@ static void __exit nf_nat_cleanup(void)
 	nf_ct_extend_unregister(&nat_extend);
 	rcu_assign_pointer(nf_nat_seq_adjust_hook, NULL);
 	rcu_assign_pointer(nfnetlink_parse_nat_setup_hook, NULL);
+	rcu_assign_pointer(nf_ct_nat_offset, NULL);
 	synchronize_net();
 }
net/ipv4/netfilter/nf_nat_helper.c +23 -11
index 09172a6..f9520fa 100644
@@ -73,6 +73,28 @@ adjust_tcp_sequence(u32 seq,
 	DUMP_OFFSET(this_way);
 }
 
+/* Get the offset value, for conntrack */
+s16 nf_nat_get_offset(const struct nf_conn *ct,
+		      enum ip_conntrack_dir dir,
+		      u32 seq)
+{
+	struct nf_conn_nat *nat = nfct_nat(ct);
+	struct nf_nat_seq *this_way;
+	s16 offset;
+
+	if (!nat)
+		return 0;
+
+	this_way = &nat->seq[dir];
+	spin_lock_bh(&nf_nat_seqofs_lock);
+	offset = after(seq, this_way->correction_pos)
+		 ? this_way->offset_after : this_way->offset_before;
+	spin_unlock_bh(&nf_nat_seqofs_lock);
+
+	return offset;
+}
+EXPORT_SYMBOL_GPL(nf_nat_get_offset);
+
 /* Frobs data inside this packet, which is linear. */
 static void mangle_contents(struct sk_buff *skb,
 			    unsigned int dataoff,

@@ -189,11 +211,6 @@ nf_nat_mangle_tcp_packet(struct sk_buff *skb,
 		adjust_tcp_sequence(ntohl(tcph->seq),
 				    (int)rep_len - (int)match_len,
 				    ct, ctinfo);
-		/* Tell TCP window tracking about seq change */
-		nf_conntrack_tcp_update(skb, ip_hdrlen(skb),
-					ct, CTINFO2DIR(ctinfo),
-					(int)rep_len - (int)match_len);
-
 		nf_conntrack_event_cache(IPCT_NATSEQADJ, ct);
 	}
 	return 1;

@@ -415,12 +432,7 @@ nf_nat_seq_adjust(struct sk_buff *skb,
 	tcph->seq = newseq;
 	tcph->ack_seq = newack;
 
-	if (!nf_nat_sack_adjust(skb, tcph, ct, ctinfo))
-		return 0;
-
-	nf_conntrack_tcp_update(skb, ip_hdrlen(skb), ct, dir, seqoff);
-
-	return 1;
+	return nf_nat_sack_adjust(skb, tcph, ct, ctinfo);
 }
 
 /* Setup NAT on this expected conntrack so it follows master. */
net/netfilter/nf_conntrack_core.c +8 -0
index b371098..805b6a9 100644
@@ -1350,6 +1350,11 @@ err_stat:
 	return ret;
 }
 
+s16 (*nf_ct_nat_offset)(const struct nf_conn *ct,
+			enum ip_conntrack_dir dir,
+			u32 seq);
+EXPORT_SYMBOL_GPL(nf_ct_nat_offset);
+
 int nf_conntrack_init(struct net *net)
 {
 	int ret;

@@ -1367,6 +1372,9 @@ int nf_conntrack_init(struct net *net)
 		/* For use by REJECT target */
 		rcu_assign_pointer(ip_ct_attach, nf_conntrack_attach);
 		rcu_assign_pointer(nf_ct_destroy, destroy_conntrack);
+
+		/* Howto get NAT offsets */
+		rcu_assign_pointer(nf_ct_nat_offset, NULL);
 	}
 	return 0;
net/netfilter/nf_conntrack_proto_tcp.c +26 -38

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