l2tp: use rcu_dereference_sk_user_data() in l2tp_udp_encap_recv()

BugLink: https://bugs.launchpad.net/bugs/1832749
[ 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 <edumazet@google.com>
Cc: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index fa789c082c3e5ad4ff63e8ea3837ac5df725fdfb..52b5a2797c0c6e85e0cd2f8203616b536b86d178 100644 (file)
--- 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;