From f2dd495a8d589371289981d5ed33e6873df94ecc Mon Sep 17 00:00:00 2001
From: Pablo Neira Ayuso <pablo@netfilter.org>
Date: Mon, 21 Mar 2022 11:38:32 +0100
Subject: [PATCH] netfilter: nf_conntrack_tcp: preserve liberal flag in tcp
 options
Git-commit: f2dd495a8d589371289981d5ed33e6873df94ecc
Patch-mainline: v5.18-rc1
References: bsc#1199035

Do not reset IP_CT_TCP_FLAG_BE_LIBERAL flag in out-of-sync scenarios
coming before the TCP window tracking, otherwise such connections will
fail in the window check.

Update tcp_options() to leave this flag in place and add a new helper
function to reset the tcp window state.

Based on patch from Sven Auhagen.

Fixes: c4832c7bbc3f ("netfilter: nf_ct_tcp: improve out-of-sync situation in TCP tracking")
Tested-by: Sven Auhagen <sven.auhagen@voleatech.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Acked-by: Ali Abdallah <ali.abdallah@suse.com>
---
 net/netfilter/nf_conntrack_proto_tcp.c |   17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -393,8 +393,8 @@ static void tcp_options(const struct sk_
 				 length, buff);
 	BUG_ON(ptr == NULL);
 
-	state->td_scale =
-	state->flags = 0;
+	state->td_scale = 0;
+	state->flags &= IP_CT_TCP_FLAG_BE_LIBERAL;
 
 	while (length > 0) {
 		int opcode=*ptr++;
@@ -859,6 +859,16 @@ static bool tcp_can_early_drop(const str
 	return false;
 }
 
+static void nf_ct_tcp_state_reset(struct ip_ct_tcp_state *state)
+{
+	state->td_end		= 0;
+	state->td_maxend	= 0;
+	state->td_maxwin	= 0;
+	state->td_maxack	= 0;
+	state->td_scale		= 0;
+	state->flags		&= IP_CT_TCP_FLAG_BE_LIBERAL;
+}
+
 /* Returns verdict for packet, or -1 for invalid. */
 static int tcp_packet(struct nf_conn *ct,
 		      const struct sk_buff *skb,
@@ -960,8 +970,7 @@ static int tcp_packet(struct nf_conn *ct
 			ct->proto.tcp.last_flags &= ~IP_CT_EXP_CHALLENGE_ACK;
 			ct->proto.tcp.seen[ct->proto.tcp.last_dir].flags =
 				ct->proto.tcp.last_flags;
-			memset(&ct->proto.tcp.seen[dir], 0,
-			       sizeof(struct ip_ct_tcp_state));
+			nf_ct_tcp_state_reset(&ct->proto.tcp.seen[dir]);
 			break;
 		}
 		ct->proto.tcp.last_index = index;