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authorFlorian Westphal <fw@strlen.de>2023-01-11 16:42:32 +0300
committerPablo Neira Ayuso <pablo@netfilter.org>2023-01-18 01:00:06 +0300
commitc410cb974f2ba562920ecb8492ee66945dcf88af (patch)
treeaf479529f15ee899a919e0a853b56f45555d8a8f /net/netfilter
parent1f3bd64ad921f051254591fbed04fd30b306cde6 (diff)
downloadlinux-c410cb974f2ba562920ecb8492ee66945dcf88af.tar.xz
netfilter: conntrack: handle tcp challenge acks during connection reuse
When a connection is re-used, following can happen: [ connection starts to close, fin sent in either direction ] > syn # initator quickly reuses connection < ack # peer sends a challenge ack > rst # rst, sequence number == ack_seq of previous challenge ack > syn # this syn is expected to pass Problem is that the rst will fail window validation, so it gets tagged as invalid. If ruleset drops such packets, we get repeated syn-retransmits until initator gives up or peer starts responding with syn/ack. Before the commit indicated in the "Fixes" tag below this used to work: The challenge-ack made conntrack re-init state based on the challenge ack itself, so the following rst would pass window validation. Add challenge-ack support: If we get ack for syn, record the ack_seq, and then check if the rst sequence number matches the last ack number seen in reverse direction. Fixes: c7aab4f17021 ("netfilter: nf_conntrack_tcp: re-init for syn packets only") Reported-by: Michal Tesar <mtesar@redhat.com> Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Diffstat (limited to 'net/netfilter')
-rw-r--r--net/netfilter/nf_conntrack_proto_tcp.c15
1 files changed, 15 insertions, 0 deletions
diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index 656631083177..3ac1af6f59fc 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -1068,6 +1068,13 @@ int nf_conntrack_tcp_packet(struct nf_conn *ct,
ct->proto.tcp.last_flags |=
IP_CT_EXP_CHALLENGE_ACK;
}
+
+ /* possible challenge ack reply to syn */
+ if (old_state == TCP_CONNTRACK_SYN_SENT &&
+ index == TCP_ACK_SET &&
+ dir == IP_CT_DIR_REPLY)
+ ct->proto.tcp.last_ack = ntohl(th->ack_seq);
+
spin_unlock_bh(&ct->lock);
nf_ct_l4proto_log_invalid(skb, ct, state,
"packet (index %d) in dir %d ignored, state %s",
@@ -1193,6 +1200,14 @@ int nf_conntrack_tcp_packet(struct nf_conn *ct,
* segments we ignored. */
goto in_window;
}
+
+ /* Reset in response to a challenge-ack we let through earlier */
+ if (old_state == TCP_CONNTRACK_SYN_SENT &&
+ ct->proto.tcp.last_index == TCP_ACK_SET &&
+ ct->proto.tcp.last_dir == IP_CT_DIR_REPLY &&
+ ntohl(th->seq) == ct->proto.tcp.last_ack)
+ goto in_window;
+
break;
default:
/* Keep compilers happy. */