Commit be0502a3f2e9 ("netfilter: conntrack: tcp: only close if RST matches exact sequence") keeps an established conntrack entry in ESTABLISHED when an in-window RST does not match the expected sequence number exactly, so the endpoint can validate the RST with a challenge ACK. The timeout selection nevertheless uses the CLOSE timeout for every RST packet. The bug is that timeout selection is based on the packet type, not on the state transition result: even when RST validation keeps new_state in ESTABLISHED, the timeout is still forced to TCP_CONNTRACK_CLOSE. Linux TCP independently rate limits challenge ACKs per socket. A second non-exact RST can therefore arrive after the first challenge ACK has restored the timeout but before the rate limit expires. The second RST lowers the timeout to 10 seconds again while the endpoint suppresses the second challenge ACK, allowing the conntrack entry to expire while both TCP endpoints remain established. Using the ESTABLISHED timeout for non-exact RSTs would avoid this short expiration window, but it could also retain stale entries for the five-day default because conntrack cannot reliably match the endpoint's exact TCP state. Use the UNACK timeout for RST packets that do not move the conntrack entry to TCP_CONNTRACK_CLOSE. Exact-match RSTs and accepted RST packet trains still use the CLOSE timeout because their state transition result is CLOSE. This avoids the exploitable 10-second expiration window for non-exact RSTs while preserving the short timeout for RSTs that conntrack accepts as closing the flow. Fixes: be0502a3f2e9 ("netfilter: conntrack: tcp: only close if RST matches exact sequence") Suggested-by: Florian Westphal Reported-by: Minghao Zhang Reported-by: Jianjun Chen Signed-off-by: Minghao Zhang --- net/netfilter/nf_conntrack_proto_tcp.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c index 0c1d086e9..849471101 100644 --- a/net/netfilter/nf_conntrack_proto_tcp.c +++ b/net/netfilter/nf_conntrack_proto_tcp.c @@ -1280,8 +1280,11 @@ int nf_conntrack_tcp_packet(struct nf_conn *ct, if (ct->proto.tcp.retrans >= tn->tcp_max_retrans && timeouts[new_state] > timeouts[TCP_CONNTRACK_RETRANS]) timeout = timeouts[TCP_CONNTRACK_RETRANS]; - else if (unlikely(index == TCP_RST_SET)) + else if (unlikely(index == TCP_RST_SET && + new_state == TCP_CONNTRACK_CLOSE)) timeout = timeouts[TCP_CONNTRACK_CLOSE]; + else if (unlikely(index == TCP_RST_SET)) + timeout = timeouts[TCP_CONNTRACK_UNACK]; else if ((ct->proto.tcp.seen[0].flags | ct->proto.tcp.seen[1].flags) & IP_CT_TCP_FLAG_DATA_UNACKNOWLEDGED && timeouts[new_state] > timeouts[TCP_CONNTRACK_UNACK]) -- 2.43.0