[PATCH 6.1 116/313] l2tp: prevent lockdep issue in l2tp_tunnel_register()

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From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ Upstream commit b9fb10d131b8c84af9bb14e2078d5c63600c7dea ]

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@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Link: https://lore.kernel.org/netdev/20230114030137.672706-1-xiyou.wangcong@xxxxxxxxx/T/#m1164ff20628671b0f326a24cb106ab3239c70ce3
Cc: Cong Wang <cong.wang@xxxxxxxxxxxxx>
Cc: Guillaume Nault <gnault@xxxxxxxxxx>
Reviewed-by: Guillaume Nault <gnault@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 b6554e32bb12..03608d3ded4b 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






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