netfilter: Only allow sane values in nf_register_net_hook

This commit adds an upfront check for sane values to be passed when
registering a netfilter hook.  This will be used in a future patch for a
simplified hook list traversal.
Signed-off-by: Aaron Conole <aconole@bytheb.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/core.c

@@ -89,6 +89,11 @@ int nf_register_net_hook(struct net *net, const struct nf_hook_ops *reg)
 	struct nf_hook_entry *entry;
 	struct nf_hook_ops *elem;
 
+	if (reg->pf == NFPROTO_NETDEV &&
+	    (reg->hooknum != NF_NETDEV_INGRESS ||
+	     !reg->dev || dev_net(reg->dev) != net))
+		return -EINVAL;
+
 	entry = kmalloc(sizeof(*entry), GFP_KERNEL);
 	if (!entry)
 		return -ENOMEM;