netfilter: x_tables: never register tables by default

For historical reasons x_tables still register tables by default in the
initial namespace.
Only newly created net namespaces add the hook on demand.

This means that the init_net always pays hook cost, even if no filtering
rules are added (e.g. only used inside a single netns).

Note that the hooks are added even when 'iptables -L' is called.
This is because there is no way to tell 'iptables -A' and 'iptables -L'
apart at kernel level.

The only solution would be to register the table, but delay hook
registration until the first rule gets added (or policy gets changed).

That however means that counters are not hooked either, so 'iptables -L'
would always show 0-counters even when traffic is flowing which might be
unexpected.

This keeps table and hook registration consistent with what is already done
in non-init netns: first iptables(-save) invocation registers both table
and hooks.

This applies the same solution adopted for ebtables.
All tables register a template that contains the l3 family, the name
and a constructor function that is called when the initial table has to
be added.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 11 insertions, 12 deletions

diff --git a/net/ipv4/netfilter/arptable_filter.c b/net/ipv4/netfilter/arptable_filter.c
index 6922612df4563..3de78416ec762 100644
--- a/net/ipv4/netfilter/arptable_filter.c
+++ b/net/ipv4/netfilter/arptable_filter.c
@@ -18,15 +18,12 @@ MODULE_DESCRIPTION("arptables filter table");
 #define FILTER_VALID_HOOKS ((1 << NF_ARP_IN) | (1 << NF_ARP_OUT) | \
 			   (1 << NF_ARP_FORWARD))
 
-static int __net_init arptable_filter_table_init(struct net *net);
-
 static const struct xt_table packet_filter = {
 	.name		= "filter",
 	.valid_hooks	= FILTER_VALID_HOOKS,
 	.me		= THIS_MODULE,
 	.af		= NFPROTO_ARP,
 	.priority	= NF_IP_PRI_FILTER,
-	.table_init	= arptable_filter_table_init,
 };
 
 /* The work comes in here from netfilter.c */
@@ -39,7 +36,7 @@ arptable_filter_hook(void *priv, struct sk_buff *skb,
 
 static struct nf_hook_ops *arpfilter_ops __read_mostly;
 
-static int __net_init arptable_filter_table_init(struct net *net)
+static int arptable_filter_table_init(struct net *net)
 {
 	struct arpt_replace *repl;
 	int err;
@@ -69,30 +66,32 @@ static struct pernet_operations arptable_filter_net_ops = {
 
 static int __init arptable_filter_init(void)
 {
-	int ret;
+	int ret = xt_register_template(&packet_filter,
+				       arptable_filter_table_init);
+
+	if (ret < 0)
+		return ret;
 
 	arpfilter_ops = xt_hook_ops_alloc(&packet_filter, arptable_filter_hook);
-	if (IS_ERR(arpfilter_ops))
+	if (IS_ERR(arpfilter_ops)) {
+		xt_unregister_template(&packet_filter);
 		return PTR_ERR(arpfilter_ops);
+	}
 
 	ret = register_pernet_subsys(&arptable_filter_net_ops);
 	if (ret < 0) {
+		xt_unregister_template(&packet_filter);
 		kfree(arpfilter_ops);
 		return ret;
 	}
 
-	ret = arptable_filter_table_init(&init_net);
-	if (ret) {
-		unregister_pernet_subsys(&arptable_filter_net_ops);
-		kfree(arpfilter_ops);
-	}
-
 	return ret;
 }
 
 static void __exit arptable_filter_fini(void)
 {
 	unregister_pernet_subsys(&arptable_filter_net_ops);
+	xt_unregister_template(&packet_filter);
 	kfree(arpfilter_ops);
 }