Subject: [PATCH 07/19] l2tp: use rcu_dereference_sk_user_data() in l2tp_udp_encap_recv()

From: Eric Dumazet <[email-masked]>
Date: Tue, 23 Apr 2019 09:43:26 -0700

[ Upstream commit c1c477217882c610a2ba0268f5faf36c9c092528 ]

Canonical way to fetch sk_user_data from an encap_rcv() handler called
from UDP stack in rcu protected section is to use rcu_dereference_sk_user_data(),
otherwise compiler might read it multiple times.

Fixes: d00fa9adc528 ("il2tp: fix races with tunnel socket close")
Signed-off-by: Eric Dumazet <[email-masked]>
Cc: James Chapman <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/l2tp/l2tp_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index fa789c082c3e..52b5a2797c0c 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -909,7 +909,7 @@ int l2tp_udp_encap_recv(struct sock *sk, struct sk_buff *skb)
 {
 	struct l2tp_tunnel *tunnel;
 
-	tunnel = l2tp_tunnel(sk);
+	tunnel = rcu_dereference_sk_user_data(sk);
 	if (tunnel == NULL)
 		goto pass_up;
 
-- 
2.20.1