[PATCH net] l2tp: use rcu_dereference_sk_user_data() in l2tp_udp_encap_recv()

[Eric Dumazet]

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 <eduma...@google.com>
Cc: James Chapman <jchap...@katalix.com>
---
 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 
fed6becc5daf86afa2ad9188bb28e151244bb5a6..aee33d1320184e411dbedff72b5bf5199481e53f
 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;
 
-- 
2.21.0.593.g511ec345e18-goog