Subject: [PATCH v3 net-next] net: Find dst with sk's xfrm policy not ctl_sk

From: Sewook Seo <[email-masked]>
Date: Wed, 6 Jul 2022 06:32:43 +0000

From: sewookseo <[email-masked]>

If we set XFRM security policy by calling setsockopt with option
IPV6_XFRM_POLICY, the policy will be stored in 'sock_policy' in 'sock'
struct. However tcp_v6_send_response doesn't look up dst_entry with the
actual socket but looks up with tcp control socket. This may cause a
problem that a RST packet is sent without ESP encryption & peer's TCP
socket can't receive it.
This patch will make the function look up dest_entry with actual socket,
if the socket has XFRM policy(sock_policy), so that the TCP response
packet via this function can be encrypted, & aligned on the encrypted
TCP socket.

Tested: We encountered this problem when a TCP socket which is encrypted
in ESP transport mode encryption, receives challenge ACK at SYN_SENT
state. After receiving challenge ACK, TCP needs to send RST to
establish the socket at next SYN try. But the RST was not encrypted &
peer TCP socket still remains on ESTABLISHED state.
So we verified this with test step as below.
[Test step]
1. Making a TCP state mismatch between client(IDLE) & server(ESTABLISHED).
2. Client tries a new connection on the same TCP ports(src & dst).
3. Server will return challenge ACK instead of SYN,ACK.
4. Client will send RST to server to clear the SOCKET.
5. Client will retransmit SYN to server on the same TCP ports.
[Expected result]
The TCP connection should be established.

Effort: net
Cc: Maciej Żenczykowski <[email-masked]>
Cc: Eric Dumazet <[email-masked]>
Cc: Steffen Klassert <[email-masked]>
Cc: Sehee Lee <[email-masked]>
Signed-off-by: Sewook Seo <[email-masked]>
---
 net/ipv4/ip_output.c | 7 ++++++-
 net/ipv4/tcp_ipv4.c  | 5 +++++
 net/ipv6/tcp_ipv6.c  | 7 ++++++-
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 00b4bf26fd93..1da430c8fee2 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1704,7 +1704,12 @@ void ip_send_unicast_reply(struct sock *sk, struct sk_buff *skb,
 			   tcp_hdr(skb)->source, tcp_hdr(skb)->dest,
 			   arg->uid);
 	security_skb_classify_flow(skb, flowi4_to_flowi_common(&fl4));
-	rt = ip_route_output_key(net, &fl4);
+#ifdef CONFIG_XFRM
+	if (sk->sk_policy[XFRM_POLICY_OUT])
+		rt = ip_route_output_flow(net, &fl4, sk);
+	else
+#endif
+		rt = ip_route_output_key(net, &fl4);
 	if (IS_ERR(rt))
 		return;
 
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index fda811a5251f..3c2ab436c692 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -819,6 +819,10 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 		ctl_sk->sk_priority = (sk->sk_state == TCP_TIME_WAIT) ?
 				   inet_twsk(sk)->tw_priority : sk->sk_priority;
 		transmit_time = tcp_transmit_time(sk);
+#ifdef CONFIG_XFRM
+		if (sk->sk_policy[XFRM_POLICY_OUT] && sk_fullsock(sk))
+			xfrm_sk_clone_policy(ctl_sk, sk);
+#endif
 	}
 	ip_send_unicast_reply(ctl_sk,
 			      skb, &TCP_SKB_CB(skb)->header.h4.opt,
@@ -827,6 +831,7 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 			      transmit_time);
 
 	ctl_sk->sk_mark = 0;
+	xfrm_sk_free_policy(ctl_sk);
 	sock_net_set(ctl_sk, &init_net);
 	__TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
 	__TCP_INC_STATS(net, TCP_MIB_OUTRSTS);
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index c72448ba6dc9..8b8819c3d2c2 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -952,7 +952,12 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
 	 * Underlying function will use this to retrieve the network
 	 * namespace
 	 */
-	dst = ip6_dst_lookup_flow(sock_net(ctl_sk), ctl_sk, &fl6, NULL);
+#ifdef CONFIG_XFRM
+	if (sk && sk->sk_policy[XFRM_POLICY_OUT] && sk_fullsock(sk))
+		dst = ip6_dst_lookup_flow(net, sk, &fl6, NULL);  /* Get dst with sk's XFRM policy */
+	else
+#endif
+		dst = ip6_dst_lookup_flow(sock_net(ctl_sk), ctl_sk, &fl6, NULL);
 	if (!IS_ERR(dst)) {
 		skb_dst_set(buff, dst);
 		ip6_xmit(ctl_sk, buff, &fl6, fl6.flowi6_mark, NULL,
-- 
2.37.0.rc0.161.g10f37bed90-goog