bridge: Handle error of rtnl_register_module().

Since introduced, br_vlan_rtnl_init() has been ignoring the returned
value of rtnl_register_module(), which could fail silently.

Handling the error allows users to view a module as an all-or-nothing
thing in terms of the rtnetlink functionality.  This prevents syzkaller
from reporting spurious errors from its tests, where OOM often occurs
and module is automatically loaded.

Let's handle the errors by rtnl_register_many().

Fixes: 8dcea18 ("net: bridge: vlan: add rtm definitions and dump support")
Fixes: f26b296 ("net: bridge: vlan: add new rtm message support")
Fixes: adb3ce9 ("net: bridge: vlan: add del rtm message support")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/bridge/br_netlink.c

@@ -1920,7 +1920,10 @@ int __init br_netlink_init(void)
 {
 	int err;
 
-	br_vlan_rtnl_init();
+	err = br_vlan_rtnl_init();
+	if (err)
+		goto out;
+
 	rtnl_af_register(&br_af_ops);
 
 	err = rtnl_link_register(&br_link_ops);
@@ -1931,6 +1934,7 @@ int __init br_netlink_init(void)
 
 out_af:
 	rtnl_af_unregister(&br_af_ops);
+out:
 	return err;
 }
 

net/bridge/br_private.h

@@ -1571,7 +1571,7 @@ void br_vlan_get_stats(const struct net_bridge_vlan *v,
 void br_vlan_port_event(struct net_bridge_port *p, unsigned long event);
 int br_vlan_bridge_event(struct net_device *dev, unsigned long event,
 			 void *ptr);
-void br_vlan_rtnl_init(void);
+int br_vlan_rtnl_init(void);
 void br_vlan_rtnl_uninit(void);
 void br_vlan_notify(const struct net_bridge *br,
 		    const struct net_bridge_port *p,
@@ -1802,8 +1802,9 @@ static inline int br_vlan_bridge_event(struct net_device *dev,
 	return 0;
 }
 
-static inline void br_vlan_rtnl_init(void)
+static inline int br_vlan_rtnl_init(void)
 {
+	return 0;
 }
 
 static inline void br_vlan_rtnl_uninit(void)

net/bridge/br_vlan.c

@@ -2296,19 +2296,18 @@ static int br_vlan_rtm_process(struct sk_buff *skb, struct nlmsghdr *nlh,
 	return err;
 }
 
-void br_vlan_rtnl_init(void)
+static const struct rtnl_msg_handler br_vlan_rtnl_msg_handlers[] = {
+	{THIS_MODULE, PF_BRIDGE, RTM_NEWVLAN, br_vlan_rtm_process, NULL, 0},
+	{THIS_MODULE, PF_BRIDGE, RTM_DELVLAN, br_vlan_rtm_process, NULL, 0},
+	{THIS_MODULE, PF_BRIDGE, RTM_GETVLAN, NULL, br_vlan_rtm_dump, 0},
+};
+
+int br_vlan_rtnl_init(void)
 {
-	rtnl_register_module(THIS_MODULE, PF_BRIDGE, RTM_GETVLAN, NULL,
-			     br_vlan_rtm_dump, 0);
-	rtnl_register_module(THIS_MODULE, PF_BRIDGE, RTM_NEWVLAN,
-			     br_vlan_rtm_process, NULL, 0);
-	rtnl_register_module(THIS_MODULE, PF_BRIDGE, RTM_DELVLAN,
-			     br_vlan_rtm_process, NULL, 0);
+	return rtnl_register_many(br_vlan_rtnl_msg_handlers);
 }
 
 void br_vlan_rtnl_uninit(void)
 {
-	rtnl_unregister(PF_BRIDGE, RTM_GETVLAN);
-	rtnl_unregister(PF_BRIDGE, RTM_NEWVLAN);
-	rtnl_unregister(PF_BRIDGE, RTM_DELVLAN);
+	rtnl_unregister_many(br_vlan_rtnl_msg_handlers);
 }