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 <kadlec@blackhole.kfki.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 34 insertions, 38 deletions

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 7c9ec3dee96e..0cdfb388a191 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -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;
 
diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index 97a82ba75376..ba2b76937283 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -492,6 +492,21 @@ static void tcp_sack(const struct sk_buff *skb, unsigned int dataoff,
 	}
 }
 
+#ifdef CONFIG_NF_NAT_NEEDED
+static inline s16 nat_offset(const struct nf_conn *ct,
+			     enum ip_conntrack_dir dir,
+			     u32 seq)
+{
+	typeof(nf_ct_nat_offset) get_offset = rcu_dereference(nf_ct_nat_offset);
+
+	return get_offset != NULL ? get_offset(ct, dir, seq) : 0;
+}
+#define NAT_OFFSET(pf, ct, dir, seq) \
+	(pf == NFPROTO_IPV4 ? nat_offset(ct, dir, seq) : 0)
+#else
+#define NAT_OFFSET(pf, ct, dir, seq)	0
+#endif
+
 static bool tcp_in_window(const struct nf_conn *ct,
 			  struct ip_ct_tcp *state,
 			  enum ip_conntrack_dir dir,
@@ -506,6 +521,7 @@ static bool tcp_in_window(const struct nf_conn *ct,
 	struct ip_ct_tcp_state *receiver = &state->seen[!dir];
 	const struct nf_conntrack_tuple *tuple = &ct->tuplehash[dir].tuple;
 	__u32 seq, ack, sack, end, win, swin;
+	s16 receiver_offset;
 	bool res;
 
 	/*
@@ -519,11 +535,16 @@ static bool tcp_in_window(const struct nf_conn *ct,
 	if (receiver->flags & IP_CT_TCP_FLAG_SACK_PERM)
 		tcp_sack(skb, dataoff, tcph, &sack);
 
+	/* Take into account NAT sequence number mangling */
+	receiver_offset = NAT_OFFSET(pf, ct, !dir, ack - 1);
+	ack -= receiver_offset;
+	sack -= receiver_offset;
+
 	pr_debug("tcp_in_window: START\n");
 	pr_debug("tcp_in_window: ");
 	nf_ct_dump_tuple(tuple);
-	pr_debug("seq=%u ack=%u sack=%u win=%u end=%u\n",
-		 seq, ack, sack, win, end);
+	pr_debug("seq=%u ack=%u+(%d) sack=%u+(%d) win=%u end=%u\n",
+		 seq, ack, receiver_offset, sack, receiver_offset, win, end);
 	pr_debug("tcp_in_window: sender end=%u maxend=%u maxwin=%u scale=%i "
 		 "receiver end=%u maxend=%u maxwin=%u scale=%i\n",
 		 sender->td_end, sender->td_maxend, sender->td_maxwin,
@@ -613,8 +634,8 @@ static bool tcp_in_window(const struct nf_conn *ct,
 
 	pr_debug("tcp_in_window: ");
 	nf_ct_dump_tuple(tuple);
-	pr_debug("seq=%u ack=%u sack =%u win=%u end=%u\n",
-		 seq, ack, sack, win, end);
+	pr_debug("seq=%u ack=%u+(%d) sack=%u+(%d) win=%u end=%u\n",
+		 seq, ack, receiver_offset, sack, receiver_offset, win, end);
 	pr_debug("tcp_in_window: sender end=%u maxend=%u maxwin=%u scale=%i "
 		 "receiver end=%u maxend=%u maxwin=%u scale=%i\n",
 		 sender->td_end, sender->td_maxend, sender->td_maxwin,
@@ -700,7 +721,7 @@ static bool tcp_in_window(const struct nf_conn *ct,
 			before(seq, sender->td_maxend + 1) ?
 			after(end, sender->td_end - receiver->td_maxwin - 1) ?
 			before(sack, receiver->td_end + 1) ?
-			after(ack, receiver->td_end - MAXACKWINDOW(sender)) ? "BUG"
+			after(sack, receiver->td_end - MAXACKWINDOW(sender) - 1) ? "BUG"
 			: "ACK is under the lower bound (possible overly delayed ACK)"
 			: "ACK is over the upper bound (ACKed data not seen yet)"
 			: "SEQ is under the lower bound (already ACKed data retransmitted)"
@@ -715,39 +736,6 @@ static bool tcp_in_window(const struct nf_conn *ct,
 	return res;
 }
 
-#ifdef CONFIG_NF_NAT_NEEDED
-/* Update sender->td_end after NAT successfully mangled the packet */
-/* Caller must linearize skb at tcp header. */
-void nf_conntrack_tcp_update(const struct sk_buff *skb,
-			     unsigned int dataoff,
-			     struct nf_conn *ct, int dir,
-			     s16 offset)
-{
-	const struct tcphdr *tcph = (const void *)skb->data + dataoff;
-	const struct ip_ct_tcp_state *sender = &ct->proto.tcp.seen[dir];
-	const struct ip_ct_tcp_state *receiver = &ct->proto.tcp.seen[!dir];
-	__u32 end;
-
-	end = segment_seq_plus_len(ntohl(tcph->seq), skb->len, dataoff, tcph);
-
-	spin_lock_bh(&ct->lock);
-	/*
-	 * We have to worry for the ack in the reply packet only...
-	 */
-	if (ct->proto.tcp.seen[dir].td_end + offset == end)
-		ct->proto.tcp.seen[dir].td_end = end;
-	ct->proto.tcp.last_end = end;
-	spin_unlock_bh(&ct->lock);
-	pr_debug("tcp_update: sender end=%u maxend=%u maxwin=%u scale=%i "
-		 "receiver end=%u maxend=%u maxwin=%u scale=%i\n",
-		 sender->td_end, sender->td_maxend, sender->td_maxwin,
-		 sender->td_scale,
-		 receiver->td_end, receiver->td_maxend, receiver->td_maxwin,
-		 receiver->td_scale);
-}
-EXPORT_SYMBOL_GPL(nf_conntrack_tcp_update);
-#endif
-
 #define	TH_FIN	0x01
 #define	TH_SYN	0x02
 #define	TH_RST	0x04