[PATCH 4.19 180/338] netfilter: nf_conntrack_tcp: preserve liberal flag in tcp options

Greg Kroah-Hartman
2022-04-14T14:01:53Z

From: Pablo Neira Ayuso <pablo@netfilter.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@voleatech.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.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 40f8a1252394..66cda5e2d6b9 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -362,8 +362,8 @@ 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++;
@@ -784,6 +784,16 @@ static bool nf_conntrack_tcp_established(const struct nf_conn *ct)
test_bit(IPS_ASSURED_BIT, &ct->status);
}

+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,
@@ -882,8 +892,7 @@ 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