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>

4 files changed, 60 insertions, 49 deletions

diff --git a/net/ipv4/netfilter/nf_nat_core.c b/net/ipv4/netfilter/nf_nat_core.c
index 68afc6ecd343..fe1a64479dd0 100644
--- a/net/ipv4/netfilter/nf_nat_core.c
+++ b/net/ipv4/netfilter/nf_nat_core.c
@@ -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();
 }
 
diff --git a/net/ipv4/netfilter/nf_nat_helper.c b/net/ipv4/netfilter/nf_nat_helper.c
index 09172a65d9b6..f9520fa3aba9 100644
--- a/net/ipv4/netfilter/nf_nat_helper.c
+++ b/net/ipv4/netfilter/nf_nat_helper.c
@@ -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. */
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