From: Felix Fietkau <nbd@nbd.name>
Subject: netfilter: optional tcp window check

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Christian 'Ansuel' Marangi <ansuelsmth@gmail.com>
---
 net/netfilter/nf_conntrack_proto_tcp.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -465,6 +465,9 @@ static bool tcp_in_window(struct nf_conn
 	s32 receiver_offset;
 	bool res, in_recv_win;
 
+	if (tn->tcp_no_window_check)
+		return true;
+
 	/*
 	 * Get the required data from the packet.
 	 */
@@ -1191,7 +1194,7 @@ int nf_conntrack_tcp_packet(struct nf_co
 		 IP_CT_TCP_FLAG_DATA_UNACKNOWLEDGED &&
 		 timeouts[new_state] > timeouts[TCP_CONNTRACK_UNACK])
 		timeout = timeouts[TCP_CONNTRACK_UNACK];
-	else if (ct->proto.tcp.last_win == 0 &&
+	else if (!tn->tcp_no_window_check && ct->proto.tcp.last_win == 0 &&
 		 timeouts[new_state] > timeouts[TCP_CONNTRACK_RETRANS])
 		timeout = timeouts[TCP_CONNTRACK_RETRANS];
 	else
@@ -1507,6 +1510,9 @@ void nf_conntrack_tcp_init_net(struct ne
 	 */
 	tn->tcp_be_liberal = 0;
 
+	/* Skip Windows Check */
+	tn->tcp_no_window_check = 0;
+
 	/* If it's non-zero, we turn off RST sequence number check */
 	tn->tcp_ignore_invalid_rst = 0;
 
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -633,6 +633,7 @@ enum nf_ct_sysctl_index {
 #endif
 	NF_SYSCTL_CT_PROTO_TCP_LOOSE,
 	NF_SYSCTL_CT_PROTO_TCP_LIBERAL,
+	NF_SYSCTL_CT_PROTO_TCP_NO_WINDOW_CHECK,
 	NF_SYSCTL_CT_PROTO_TCP_IGNORE_INVALID_RST,
 	NF_SYSCTL_CT_PROTO_TCP_MAX_RETRANS,
 	NF_SYSCTL_CT_PROTO_TIMEOUT_UDP,
@@ -849,6 +850,14 @@ static struct ctl_table nf_ct_sysctl_tab
 		.extra1 	= SYSCTL_ZERO,
 		.extra2 	= SYSCTL_ONE,
 	},
+	[NF_SYSCTL_CT_PROTO_TCP_NO_WINDOW_CHECK] = {
+		.procname       = "nf_conntrack_tcp_no_window_check",
+		.maxlen         = sizeof(u8),
+		.mode           = 0644,
+		.proc_handler	= proc_dou8vec_minmax,
+		.extra1 	= SYSCTL_ZERO,
+		.extra2 	= SYSCTL_ONE,
+	},
 	[NF_SYSCTL_CT_PROTO_TCP_IGNORE_INVALID_RST] = {
 		.procname	= "nf_conntrack_tcp_ignore_invalid_rst",
 		.maxlen		= sizeof(u8),
@@ -1065,6 +1074,7 @@ static void nf_conntrack_standalone_init
 
 	XASSIGN(LOOSE, &tn->tcp_loose);
 	XASSIGN(LIBERAL, &tn->tcp_be_liberal);
+	XASSIGN(NO_WINDOW_CHECK, &tn->tcp_no_window_check);
 	XASSIGN(MAX_RETRANS, &tn->tcp_max_retrans);
 	XASSIGN(IGNORE_INVALID_RST, &tn->tcp_ignore_invalid_rst);
 #undef XASSIGN
--- a/include/net/netns/conntrack.h
+++ b/include/net/netns/conntrack.h
@@ -26,6 +26,7 @@ struct nf_tcp_net {
 	unsigned int timeouts[TCP_CONNTRACK_TIMEOUT_MAX];
 	u8 tcp_loose;
 	u8 tcp_be_liberal;
+	u8 tcp_no_window_check;
 	u8 tcp_max_retrans;
 	u8 tcp_ignore_invalid_rst;
 #if IS_ENABLED(CONFIG_NF_FLOW_TABLE)
