Patch "netfilter: nf_conntrack_tcp: preserve liberal flag in tcp options" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    netfilter: nf_conntrack_tcp: preserve liberal flag in tcp options

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     netfilter-nf_conntrack_tcp-preserve-liberal-flag-in-.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit f7c6c704285e44070d48cf583949312bb03363f0
Author: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Date:   Mon Mar 21 11:38:32 2022 +0100

    netfilter: nf_conntrack_tcp: preserve liberal flag in tcp options
    
    [ 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@xxxxxxxxxxxx>
    Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index af5115e127cf..3cee5d8ee702 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -341,8 +341,8 @@ static void tcp_options(const struct sk_buff *skb,
 	if (!ptr)
 		return;
 
-	state->td_scale =
-	state->flags = 0;
+	state->td_scale = 0;
+	state->flags &= IP_CT_TCP_FLAG_BE_LIBERAL;
 
 	while (length > 0) {
 		int opcode=*ptr++;
@@ -839,6 +839,16 @@ static bool tcp_can_early_drop(const struct nf_conn *ct)
 	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. */
 int nf_conntrack_tcp_packet(struct nf_conn *ct,
 			    struct sk_buff *skb,
@@ -945,8 +955,7 @@ int nf_conntrack_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;