net/af_packet: registration process optimization in packet_init()

Now, register_pernet_subsys() and register_netdevice_notifier() are both
after sock_register(). It can create PF_PACKET socket and process socket
once sock_register() successfully. It is possible PF_PACKET socket is
creating but register_pernet_subsys() and register_netdevice_notifier()
are not registered yet. Thus net->packet.sklist_lock and net->packet.sklist
will be accessed without initialization that is done in packet_net_init().
Although this is a low probability scenario.

Move register_pernet_subsys() and register_netdevice_notifier() to the
front in packet_init(). Correspondingly, adjust the unregister process
in packet_exit().
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/packet/af_packet.c

@@ -4725,37 +4725,37 @@ static struct pernet_operations packet_net_ops = {
 
 static void __exit packet_exit(void)
 {
-	unregister_netdevice_notifier(&packet_netdev_notifier);
-	unregister_pernet_subsys(&packet_net_ops);
 	sock_unregister(PF_PACKET);
 	proto_unregister(&packet_proto);
+	unregister_netdevice_notifier(&packet_netdev_notifier);
+	unregister_pernet_subsys(&packet_net_ops);
 }
 
 static int __init packet_init(void)
 {
 	int rc;
 
-	rc = proto_register(&packet_proto, 0);
-	if (rc)
-		goto out;
-	rc = sock_register(&packet_family_ops);
-	if (rc)
-		goto out_proto;
 	rc = register_pernet_subsys(&packet_net_ops);
 	if (rc)
-		goto out_sock;
+		goto out;
 	rc = register_netdevice_notifier(&packet_netdev_notifier);
 	if (rc)
 		goto out_pernet;
+	rc = proto_register(&packet_proto, 0);
+	if (rc)
+		goto out_notifier;
+	rc = sock_register(&packet_family_ops);
+	if (rc)
+		goto out_proto;
 
 	return 0;
 
-out_pernet:
-	unregister_pernet_subsys(&packet_net_ops);
-out_sock:
-	sock_unregister(PF_PACKET);
 out_proto:
 	proto_unregister(&packet_proto);
+out_notifier:
+	unregister_netdevice_notifier(&packet_netdev_notifier);
+out_pernet:
+	unregister_pernet_subsys(&packet_net_ops);
 out:
 	return rc;
 }