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ovpn: tcp - don't deref NULL sk_socket member after tcp_close()

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When deleting a peer in case of keepalive expiration, the peer is
removed from the OpenVPN hashtable and is temporary inserted in a
"release list" for further processing.

This happens in:
ovpn_peer_keepalive_work()
  unlock_ovpn(release_list)

This processing includes detaching from the socket being used to
talk to this peer, by restoring its original proto and socket
ops/callbacks.

In case of TCP it may happen that, while the peer is sitting in
the release list, userspace decides to close the socket.
This will result in a concurrent execution of:

tcp_close(sk)
  __tcp_close(sk)
    sock_orphan(sk)
      sk_set_socket(sk, NULL)

The last function call will set sk->sk_socket to NULL.

When the releasing routine is resumed, ovpn_tcp_socket_detach()
will attempt to dereference sk->sk_socket to restore its original
ops member. This operation will crash due to sk->sk_socket being NULL.

Fix this race condition by testing-and-accessing
sk->sk_socket atomically under sk->sk_callback_lock.

Link: https://lore.kernel.org/netdev/176996279620.3109699.15382994681575380467@eldamar.lan/
Link: https://github.com/OpenVPN/ovpn-net-next/issues/29
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
Fixes: 11851cbd60 ("ovpn: implement TCP transport")
Link: https://patch.msgid.link/20260212213130.11497-1-antonio@openvpn.net
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Antonio Quartulli 2026-02-12 22:31:19 +01:00 committed by Paolo Abeni
parent e74ff27fc6
commit 94560267d6
1 changed files with 13 additions and 1 deletions
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14
drivers/net/ovpn/tcp.c
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@ -199,7 +199,19 @@ void ovpn_tcp_socket_detach(struct ovpn_socket *ovpn_sock)
sk->sk_data_ready = peer->tcp.sk_cb.sk_data_ready;
sk->sk_write_space = peer->tcp.sk_cb.sk_write_space;
sk->sk_prot = peer->tcp.sk_cb.prot;
sk->sk_socket->ops = peer->tcp.sk_cb.ops;
/* tcp_close() may race this function and could set
* sk->sk_socket to NULL. It does so by invoking
* sock_orphan(), which holds sk_callback_lock before
* doing the assignment.
*
* For this reason we acquire the same lock to avoid
* sk_socket to disappear under our feet
*/
write_lock_bh(&sk->sk_callback_lock);
if (sk->sk_socket)
sk->sk_socket->ops = peer->tcp.sk_cb.ops;
write_unlock_bh(&sk->sk_callback_lock);
rcu_assign_sk_user_data(sk, NULL);
}