| Message ID | 20260511144314.183870-1-hamzamahfooz@linux.microsoft.com |
|---|---|
| State | Accepted, archived |
| Headers | show |
| Series | [nf] netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check | expand |
diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c index b67426c2189b..e99ab1e88e9f 100644 --- a/net/netfilter/nf_conntrack_proto_tcp.c +++ b/net/netfilter/nf_conntrack_proto_tcp.c @@ -1221,7 +1221,8 @@ int nf_conntrack_tcp_packet(struct nf_conn *ct, new_state = old_state; } if (((test_bit(IPS_SEEN_REPLY_BIT, &ct->status) - && ct->proto.tcp.last_index == TCP_SYN_SET) + && ct->proto.tcp.last_index == TCP_SYN_SET + && ct->proto.tcp.last_dir != dir) || (!test_bit(IPS_ASSURED_BIT, &ct->status) && ct->proto.tcp.last_index == TCP_ACK_SET)) && ntohl(th->ack_seq) == ct->proto.tcp.last_end) {
An unintended behavior in the TCP conntrack state machine allows a connection to be forced into the CLOSE state using an RST packet with an invalid sequence number. Specifically, after a SYN packet is observed, an RST with an invalid SEQ can transition the conntrack entry to TCP_CONNTRACK_CLOSE, regardless of whether the RST corresponds to the expected reply direction. The relevant code path assumes the RST is a response to an outgoing SYN, but does not validate packet direction or ensure that a matching SYN was actually sent in the opposite direction. As a result, a crafted packet sequence consisting of a SYN followed by an invalid-sequence RST can prematurely terminate an active NAT entry. This makes connection teardown easier than intended. So, tighten the state transition logic to ensure that RST-triggered CLOSE transitions only occur when the RST is a valid response to a previously observed SYN in the correct direction. Cc: stable@vger.kernel.org Fixes: 9fb9cbb1082d ("[NETFILTER]: Add nf_conntrack subsystem.") Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com> --- net/netfilter/nf_conntrack_proto_tcp.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)