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, 6 insertions, 11 deletions

diff --git a/net/ipv4/netfilter/iptable_mangle.c b/net/ipv4/netfilter/iptable_mangle.c
index 2abc3836f391..b52a4c8a14fc 100644
--- a/net/ipv4/netfilter/iptable_mangle.c
+++ b/net/ipv4/netfilter/iptable_mangle.c
@@ -25,15 +25,12 @@ MODULE_DESCRIPTION("iptables mangle table");
 			    (1 << NF_INET_LOCAL_OUT) | \
 			    (1 << NF_INET_POST_ROUTING))
 
-static int __net_init iptable_mangle_table_init(struct net *net);
-
 static const struct xt_table packet_mangler = {
 	.name		= "mangle",
 	.valid_hooks	= MANGLE_VALID_HOOKS,
 	.me		= THIS_MODULE,
 	.af		= NFPROTO_IPV4,
 	.priority	= NF_IP_PRI_MANGLE,
-	.table_init	= iptable_mangle_table_init,
 };
 
 static unsigned int
@@ -83,7 +80,7 @@ iptable_mangle_hook(void *priv,
 }
 
 static struct nf_hook_ops *mangle_ops __read_mostly;
-static int __net_init iptable_mangle_table_init(struct net *net)
+static int iptable_mangle_table_init(struct net *net)
 {
 	struct ipt_replace *repl;
 	int ret;
@@ -113,32 +110,30 @@ static struct pernet_operations iptable_mangle_net_ops = {
 
 static int __init iptable_mangle_init(void)
 {
-	int ret;
+	int ret = xt_register_template(&packet_mangler,
+				       iptable_mangle_table_init);
 
 	mangle_ops = xt_hook_ops_alloc(&packet_mangler, iptable_mangle_hook);
 	if (IS_ERR(mangle_ops)) {
+		xt_unregister_template(&packet_mangler);
 		ret = PTR_ERR(mangle_ops);
 		return ret;
 	}
 
 	ret = register_pernet_subsys(&iptable_mangle_net_ops);
 	if (ret < 0) {
+		xt_unregister_template(&packet_mangler);
 		kfree(mangle_ops);
 		return ret;
 	}
 
-	ret = iptable_mangle_table_init(&init_net);
-	if (ret) {
-		unregister_pernet_subsys(&iptable_mangle_net_ops);
-		kfree(mangle_ops);
-	}
-
 	return ret;
 }
 
 static void __exit iptable_mangle_fini(void)
 {
 	unregister_pernet_subsys(&iptable_mangle_net_ops);
+	xt_unregister_template(&packet_mangler);
 	kfree(mangle_ops);
 }