[PATCH] netfilter: conntrack: Reset the max ACK flag on SYN in ignore state

[PATCH] netfilter: conntrack: Reset the max ACK flag on SYN in ignore state

[Ali Abdallah]

In ignore state, we let SYN goes in original, the server might respond
with RST/ACK, and that RST packet is erroneously dropped because of the
flag IP_CT_TCP_FLAG_MAXACK_SET being already set.

Signed-off-by: Ali Abdallah <aabdallah@suse.de>
---
 net/netfilter/nf_conntrack_proto_tcp.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index ec23330687a5..02fab7a8ec92 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -963,6 +963,10 @@ int nf_conntrack_tcp_packet(struct nf_conn *ct,
 
 			ct->proto.tcp.last_flags =
 			ct->proto.tcp.last_wscale = 0;
+			/* Reset the max ack flag so in case the server replies
+			 * with RST/ACK it will not be marked as an invalid rst.
+			 */
+			ct->proto.tcp.seen[dir].flags &= ~IP_CT_TCP_FLAG_MAXACK_SET;
 			tcp_options(skb, dataoff, th, &seen);
 			if (seen.flags & IP_CT_TCP_FLAG_WINDOW_SCALE) {
 				ct->proto.tcp.last_flags |=
-- 
2.26.2

Re: [PATCH] netfilter: conntrack: Reset the max ACK flag on SYN in ignore state

[Florian Westphal]

Ali Abdallah <ali.abdallah@suse.com> wrote:
> In ignore state, we let SYN goes in original, the server might respond
> with RST/ACK, and that RST packet is erroneously dropped because of the
> flag IP_CT_TCP_FLAG_MAXACK_SET being already set.

Acked-by: Florian Westphal <fw@strlen.de>