netfilter: synproxy: fix rst sequence number mismatch

14:51:00.024418 IP 192.168.122.1.41462 > netfilter.90: Flags [S], seq
4023580551,
14:51:00.024454 IP netfilter.90 > 192.168.122.1.41462: Flags [S.], seq
727560212, ack 4023580552,
14:51:00.024524 IP 192.168.122.1.41462 > netfilter.90: Flags [.], ack 1,

Note: here, synproxy will send a SYN to the real server, as the 3whs was
completed sucessfully. Instead of a syn/ack that we can intercept, we instead
received a reset packet from the real backend, that we forward to the original
client. However, we don't use the correct sequence number, so the reset is not
effective in closing the connection coming from the client.

14:51:00.024550 IP netfilter.90 > 192.168.122.1.41462: Flags [R.], seq
3567407084,
14:51:00.231196 IP 192.168.122.1.41462 > netfilter.90: Flags [.], ack 1,
14:51:00.647911 IP 192.168.122.1.41462 > netfilter.90: Flags [.], ack 1,
14:51:01.474395 IP 192.168.122.1.41462 > netfilter.90: Flags [.], ack 1,

Fixes: 48b1de4c110a ("netfilter: add SYNPROXY core/target")
Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nf_synproxy_core.c b/net/netfilter/nf_synproxy_core.c
index 09718e5a9e41384d667c6b26870ce0d61f945894..c769462a839e068bb7fea42f248d40bf0d5505fb 100644 (file)
--- a/net/netfilter/nf_synproxy_core.c
+++ b/net/netfilter/nf_synproxy_core.c
@@ -687,7 +687,7 @@ ipv4_synproxy_hook(void *priv, struct sk_buff *skb,
        state = &ct->proto.tcp;
        switch (state->state) {
        case TCP_CONNTRACK_CLOSE:
-               if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
+               if (th->rst && CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) {
                        nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
                                                      ntohl(th->seq) + 1);
                        break;
@@ -1111,7 +1111,7 @@ ipv6_synproxy_hook(void *priv, struct sk_buff *skb,
        state = &ct->proto.tcp;
        switch (state->state) {
        case TCP_CONNTRACK_CLOSE:
-               if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
+               if (th->rst && CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) {
                        nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
                                                      ntohl(th->seq) + 1);
                        break;