netdev - [PATCH net] l2tp: prevent lockdep issue in l2tp_tunnel

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Date:   Tue, 17 Jan 2023 11:01:31 +0000
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        Eric Dumazet <edumazet@...gle.com>,
        syzbot+bbd35b345c7cab0d9a08@...kaller.appspotmail.com,
        Cong Wang <cong.wang@...edance.com>,
        Guillaume Nault <gnault@...hat.com>
Subject: [PATCH net] l2tp: prevent lockdep issue in l2tp_tunnel_register()

lockdep complains with the following lock/unlock sequence:

     lock_sock(sk);
     write_lock_bh(&sk->sk_callback_lock);
[1]  release_sock(sk);
[2]  write_unlock_bh(&sk->sk_callback_lock);

We need to swap [1] and [2] to fix this issue.

Fixes: 0b2c59720e65 ("l2tp: close all race conditions in l2tp_tunnel_register()")
Reported-by: syzbot+bbd35b345c7cab0d9a08@...kaller.appspotmail.com
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Link: https://lore.kernel.org/netdev/20230114030137.672706-1-xiyou.wangcong@gmail.com/T/#m1164ff20628671b0f326a24cb106ab3239c70ce3
Cc: Cong Wang <cong.wang@...edance.com>
Cc: Guillaume Nault <gnault@...hat.com>
---
 net/l2tp/l2tp_core.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index b6554e32bb12ae7813cc06c01e4d1380af667375..03608d3ded4b83d1e59e064e482f54cffcdf5240 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1483,10 +1483,8 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
 	lock_sock(sk);
 	write_lock_bh(&sk->sk_callback_lock);
 	ret = l2tp_validate_socket(sk, net, tunnel->encap);
-	if (ret < 0) {
-		release_sock(sk);
+	if (ret < 0)
 		goto err_inval_sock;
-	}
 	rcu_assign_sk_user_data(sk, tunnel);
 	write_unlock_bh(&sk->sk_callback_lock);
 
@@ -1523,6 +1521,7 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
 
 err_inval_sock:
 	write_unlock_bh(&sk->sk_callback_lock);
+	release_sock(sk);
 
 	if (tunnel->fd < 0)
 		sock_release(sock);
-- 
2.39.0.314.g84b9a713c41-goog