phonet: Handle error of rtnl_register_module().

Before commit addf9b9 ("net: rtnetlink: use rcu to free rtnl
message handlers"), once the first rtnl_register_module() allocated
rtnl_msg_handlers[PF_PHONET], the following calls never failed.

However, after the commit, rtnl_register_module() could fail silently
to allocate rtnl_msg_handlers[PF_PHONET][msgtype] and requires error
handling for each call.

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 use rtnl_register_many() to handle the errors easily.

Fixes: addf9b9 ("net: rtnetlink: use rcu to free rtnl message handlers")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Acked-by: Rémi Denis-Courmont <courmisch@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/phonet/pn_netlink.c

@@ -285,23 +285,17 @@ static int route_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
 	return err;
 }
 
+static const struct rtnl_msg_handler phonet_rtnl_msg_handlers[] __initdata_or_module = {
+	{THIS_MODULE, PF_PHONET, RTM_NEWADDR, addr_doit, NULL, 0},
+	{THIS_MODULE, PF_PHONET, RTM_DELADDR, addr_doit, NULL, 0},
+	{THIS_MODULE, PF_PHONET, RTM_GETADDR, NULL, getaddr_dumpit, 0},
+	{THIS_MODULE, PF_PHONET, RTM_NEWROUTE, route_doit, NULL, 0},
+	{THIS_MODULE, PF_PHONET, RTM_DELROUTE, route_doit, NULL, 0},
+	{THIS_MODULE, PF_PHONET, RTM_GETROUTE, NULL, route_dumpit,
+	 RTNL_FLAG_DUMP_UNLOCKED},
+};
+
 int __init phonet_netlink_register(void)
 {
-	int err = rtnl_register_module(THIS_MODULE, PF_PHONET, RTM_NEWADDR,
-				       addr_doit, NULL, 0);
-	if (err)
-		return err;
-
-	/* Further rtnl_register_module() cannot fail */
-	rtnl_register_module(THIS_MODULE, PF_PHONET, RTM_DELADDR,
-			     addr_doit, NULL, 0);
-	rtnl_register_module(THIS_MODULE, PF_PHONET, RTM_GETADDR,
-			     NULL, getaddr_dumpit, 0);
-	rtnl_register_module(THIS_MODULE, PF_PHONET, RTM_NEWROUTE,
-			     route_doit, NULL, 0);
-	rtnl_register_module(THIS_MODULE, PF_PHONET, RTM_DELROUTE,
-			     route_doit, NULL, 0);
-	rtnl_register_module(THIS_MODULE, PF_PHONET, RTM_GETROUTE,
-			     NULL, route_dumpit, RTNL_FLAG_DUMP_UNLOCKED);
-	return 0;
+	return rtnl_register_many(phonet_rtnl_msg_handlers);
 }