linux-kernel - [PATCH 4.9 119/218] netfilter: nf_conntrack_tcp: preserve liberal flag in tcp options

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Message-Id: <20220418121202.998475889@linuxfoundation.org>
Date:   Mon, 18 Apr 2022 14:13:05 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sven Auhagen <sven.auhagen@...eatech.de>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 119/218] netfilter: nf_conntrack_tcp: preserve liberal flag in tcp options

From: Pablo Neira Ayuso <pablo@...filter.org>

[ Upstream commit f2dd495a8d589371289981d5ed33e6873df94ecc ]

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@...eatech.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/netfilter/nf_conntrack_proto_tcp.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index 69f687740c76..9e9ce570bb9e 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -390,8 +390,8 @@ static void tcp_options(const struct sk_buff *skb,
 				 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++;
@@ -806,6 +806,16 @@ static unsigned int *tcp_get_timeouts(struct net *net)
 	return tcp_pernet(net)->timeouts;
 }
 
+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,
@@ -907,8 +917,7 @@ 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;
-- 
2.34.1