[NETFILTER]: nf_conntrack_tcp: fix connection reopening

With your description I could reproduce the bug and actually you were
completely right: the code above is incorrect. Somehow I was able to
misread RFC1122 and mixed the roles :-(:

   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 it:
   [...]

The fix is as follows: if the receiver initiated an active close, then the
sender may reopen the connection - otherwise try to figure out if we hold
a dead connection.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Tested-by: Krzysztof Piotr Oledzki <ole@ans.pl>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 21 deletions

diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index df718e7c7ee4..c7075345971b 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -831,6 +831,20 @@ static int tcp_packet(struct nf_conn *conntrack,
         tuple = &conntrack->tuplehash[dir].tuple;
 
         switch (new_state) {
+        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) {
+                        /* Attempt to reopen a closed connection.
+                        * Delete this connection and look up again. */
+                        write_unlock_bh(&tcp_lock);
+                        if (del_timer(&conntrack->timeout))
+                                conntrack->timeout.function((unsigned long)
+                                                            conntrack);
+                        return -NF_REPEAT;
+                }
+                /* Fall through */
         case TCP_CONNTRACK_IGNORE:
                 /* Ignored packets:
                  *
@@ -879,27 +893,6 @@ static int tcp_packet(struct nf_conn *conntrack,
                         nf_log_packet(pf, 0, skb, NULL, NULL, NULL,
                                   "nf_ct_tcp: invalid state ");
                 return -NF_ACCEPT;
-        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)
-                    || after(ntohl(th->seq),
-                             conntrack->proto.tcp.seen[dir].td_end)) {
-                        /* Attempt to reopen a closed connection.
-                        * Delete this connection and look up again. */
-                        write_unlock_bh(&tcp_lock);
-                        if (del_timer(&conntrack->timeout))
-                                conntrack->timeout.function((unsigned long)
-                                                            conntrack);
-                        return -NF_REPEAT;
-                } else {
-                        write_unlock_bh(&tcp_lock);
-                        if (LOG_INVALID(IPPROTO_TCP))
-                                nf_log_packet(pf, 0, skb, NULL, NULL,
-                                              NULL, "nf_ct_tcp: invalid SYN");
-                        return -NF_ACCEPT;
-                }
         case TCP_CONNTRACK_CLOSE:
                 if (index == TCP_RST_SET
                     && ((test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status)