netfilter: ebtables: do not hook tables by default

If any of these modules is loaded, hooks get registered in all netns:

Before: 'unshare -n nft list hooks' shows:
family bridge hook prerouting {
	-2147483648 ebt_broute
	-0000000300 ebt_nat_hook
}
family bridge hook input {
	-0000000200 ebt_filter_hook
}
family bridge hook forward {
	-0000000200 ebt_filter_hook
}
family bridge hook output {
	+0000000100 ebt_nat_hook
	+0000000200 ebt_filter_hook
}
family bridge hook postrouting {
	+0000000300 ebt_nat_hook
}

This adds 'template 'tables' for ebtables.

Each ebtable_foo registers the table as a template, with an init function
that gets called once the first get/setsockopt call is made.

ebtables core then searches the (per netns) list of tables.
If no table is found, it searches the list of templates instead.
If a template entry exists, the init function is called which will
enable the table and register the hooks (so packets are diverted
to the table).

If no entry is found in the template list, request_module is called.

After this, hook registration is delayed until the 'ebtables'
(set/getsockopt) request is made for a given table and will only
happen in the specific namespace.

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

1 files changed, 14 insertions, 3 deletions

diff --git a/net/bridge/netfilter/ebtable_filter.c b/net/bridge/netfilter/ebtable_filter.c
index 8ec0b3736803..c0b121df4a9a 100644
--- a/net/bridge/netfilter/ebtable_filter.c
+++ b/net/bridge/netfilter/ebtable_filter.c
@@ -86,7 +86,7 @@ static const struct nf_hook_ops ebt_ops_filter[] = {
 	},
 };
 
-static int __net_init frame_filter_net_init(struct net *net)
+static int frame_filter_table_init(struct net *net)
 {
 	return ebt_register_table(net, &frame_filter, ebt_ops_filter);
 }
@@ -102,19 +102,30 @@ static void __net_exit frame_filter_net_exit(struct net *net)
 }
 
 static struct pernet_operations frame_filter_net_ops = {
-	.init = frame_filter_net_init,
 	.exit = frame_filter_net_exit,
 	.pre_exit = frame_filter_net_pre_exit,
 };
 
 static int __init ebtable_filter_init(void)
 {
-	return register_pernet_subsys(&frame_filter_net_ops);
+	int ret = ebt_register_template(&frame_filter, frame_filter_table_init);
+
+	if (ret)
+		return ret;
+
+	ret = register_pernet_subsys(&frame_filter_net_ops);
+	if (ret) {
+		ebt_unregister_template(&frame_filter);
+		return ret;
+	}
+
+	return 0;
 }
 
 static void __exit ebtable_filter_fini(void)
 {
 	unregister_pernet_subsys(&frame_filter_net_ops);
+	ebt_unregister_template(&frame_filter);
 }
 
 module_init(ebtable_filter_init);