netfilter: nf_tables: fix memory leak in nf_tables_parse_netdev_hooks()

Syzbot detected a leak in nf_tables_parse_netdev_hooks().  If the hook
already exists, then the error handling doesn't free the newest "hook".

Reported-by: [email protected]
Fixes: b75a3e8 ("netfilter: nf_tables: allow netdevice to be used only once per flowtable")
Signed-off-by: Dan Carpenter <[email protected]>
Reviewed-by: Florian Westphal <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>

Author: Dan Carpenter

net/netfilter/nf_tables_api.c

@@ -1680,6 +1680,7 @@ static int nf_tables_parse_netdev_hooks(struct net *net,
 			goto err_hook;
 		}
 		if (nft_hook_list_find(hook_list, hook)) {
+			kfree(hook);
 			err = -EEXIST;
 			goto err_hook;
 		}