netfilter: nf_tables: Fix for duplicate device in netdev hooks

When handling NETDEV_REGISTER notification, duplicate device
registration must be avoided since the device may have been added by
nft_netdev_hook_alloc() already when creating the hook.

Suggested-by: Florian Westphal <fw@strlen.de>
Reported-by: syzbot+bb9127e278fa198e110c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=bb9127e278fa198e110c
Fixes: a331b78 ("netfilter: nf_tables: Respect NETDEV_REGISTER events")
Tested-by: Helen Koike <koike@igalia.com>
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Florian Westphal <fw@strlen.de>

Author: Phil Sutter

net/netfilter/nf_tables_api.c

@@ -9688,7 +9688,7 @@ static int nft_flowtable_event(unsigned long event, struct net_device *dev,
 			break;
 		case NETDEV_REGISTER:
 			/* NOP if not matching or already registered */
-			if (!match || (changename && ops))
+			if (!match || ops)
 				continue;
 
 			ops = kzalloc_obj(struct nf_hook_ops,

net/netfilter/nft_chain_filter.c

@@ -344,7 +344,7 @@ static int nft_netdev_event(unsigned long event, struct net_device *dev,
 			break;
 		case NETDEV_REGISTER:
 			/* NOP if not matching or already registered */
-			if (!match || (changename && ops))
+			if (!match || ops)
 				continue;
 
 			ops = kmemdup(&basechain->ops,