linux-kernel - [PATCH 4.19 07/23] l2tp: use rcu_dereference_sk_user_data() in l2tp_udp_encap

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Date:   Sat,  4 May 2019 12:25:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        James Chapman <jchapman@...alix.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.19 07/23] l2tp: use rcu_dereference_sk_user_data() in l2tp_udp_encap_recv()

From: Eric Dumazet <edumazet@...gle.com>

[ 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@...gle.com>
Cc: James Chapman <jchapman@...alix.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/l2tp/l2tp_core.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 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 l2tp_tunnel *tunnel;
 
-	tunnel = l2tp_tunnel(sk);
+	tunnel = rcu_dereference_sk_user_data(sk);
 	if (tunnel == NULL)
 		goto pass_up;