netfilter: conntrack: register hooks in netns when needed by ruleset

This makes use of nf_ct_netns_get/put added in previous patch.
We add get/put functions to nf_conntrack_l3proto structure, ipv4 and ipv6
then implement use-count to track how many users (nft or xtables modules)
have a dependency on ipv4 and/or ipv6 connection tracking functionality.

When count reaches zero, the hooks are unregistered.

This delays activation of connection tracking inside a namespace until
stateful firewall rule or nat rule gets added.

This patch breaks backwards compatibility in the sense that connection
tracking won't be active anymore when the protocol tracker module is
loaded.  This breaks e.g. setups that ctnetlink for flow accounting and
the like, without any '-m conntrack' packet filter rules.

Followup patch restores old behavour and makes new delayed scheme
optional via sysctl.

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

1 files changed, 42 insertions, 12 deletions

diff --git a/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c b/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
index 389f712854f2..72fe48075b7f 100644
--- a/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
+++ b/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
@@ -34,6 +34,13 @@
 #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
 #include <net/netfilter/nf_log.h>
 
+static int conntrack6_net_id;
+static DEFINE_MUTEX(register_ipv6_hooks);
+
+struct conntrack6_net {
+	unsigned int users;
+};
+
 static bool ipv6_pkt_to_tuple(const struct sk_buff *skb, unsigned int nhoff,
 			      struct nf_conntrack_tuple *tuple)
 {
@@ -308,6 +315,36 @@ static int ipv6_nlattr_tuple_size(void)
 }
 #endif
 
+static int ipv6_hooks_register(struct net *net)
+{
+	struct conntrack6_net *cnet = net_generic(net, conntrack6_net_id);
+	int err = 0;
+
+	mutex_lock(&register_ipv6_hooks);
+	cnet->users++;
+	if (cnet->users > 1)
+		goto out_unlock;
+
+	err = nf_register_net_hooks(net, ipv6_conntrack_ops,
+				    ARRAY_SIZE(ipv6_conntrack_ops));
+	if (err)
+		cnet->users = 0;
+ out_unlock:
+	mutex_unlock(&register_ipv6_hooks);
+	return err;
+}
+
+static void ipv6_hooks_unregister(struct net *net)
+{
+	struct conntrack6_net *cnet = net_generic(net, conntrack6_net_id);
+
+	mutex_lock(&register_ipv6_hooks);
+	if (cnet->users && (--cnet->users == 0))
+		nf_unregister_net_hooks(net, ipv6_conntrack_ops,
+					ARRAY_SIZE(ipv6_conntrack_ops));
+	mutex_unlock(&register_ipv6_hooks);
+}
+
 struct nf_conntrack_l3proto nf_conntrack_l3proto_ipv6 __read_mostly = {
 	.l3proto		= PF_INET6,
 	.name			= "ipv6",
@@ -321,6 +358,8 @@ struct nf_conntrack_l3proto nf_conntrack_l3proto_ipv6 __read_mostly = {
 	.nlattr_to_tuple	= ipv6_nlattr_to_tuple,
 	.nla_policy		= ipv6_nla_policy,
 #endif
+	.net_ns_get		= ipv6_hooks_register,
+	.net_ns_put		= ipv6_hooks_unregister,
 	.me			= THIS_MODULE,
 };
 
@@ -379,6 +418,8 @@ static void ipv6_net_exit(struct net *net)
 static struct pernet_operations ipv6_net_ops = {
 	.init = ipv6_net_init,
 	.exit = ipv6_net_exit,
+	.id = &conntrack6_net_id,
+	.size = sizeof(struct conntrack6_net),
 };
 
 static int __init nf_conntrack_l3proto_ipv6_init(void)
@@ -398,18 +439,10 @@ static int __init nf_conntrack_l3proto_ipv6_init(void)
 	if (ret < 0)
 		goto cleanup_sockopt;
 
-	ret = nf_register_hooks(ipv6_conntrack_ops,
-				ARRAY_SIZE(ipv6_conntrack_ops));
-	if (ret < 0) {
-		pr_err("nf_conntrack_ipv6: can't register pre-routing defrag "
-		       "hook.\n");
-		goto cleanup_pernet;
-	}
-
 	ret = nf_ct_l4proto_register(builtin_l4proto6,
 				     ARRAY_SIZE(builtin_l4proto6));
 	if (ret < 0)
-		goto cleanup_hooks;
+		goto cleanup_pernet;
 
 	ret = nf_ct_l3proto_register(&nf_conntrack_l3proto_ipv6);
 	if (ret < 0) {
@@ -420,8 +453,6 @@ static int __init nf_conntrack_l3proto_ipv6_init(void)
 cleanup_l4proto:
 	nf_ct_l4proto_unregister(builtin_l4proto6,
 				 ARRAY_SIZE(builtin_l4proto6));
- cleanup_hooks:
-	nf_unregister_hooks(ipv6_conntrack_ops, ARRAY_SIZE(ipv6_conntrack_ops));
  cleanup_pernet:
 	unregister_pernet_subsys(&ipv6_net_ops);
  cleanup_sockopt:
@@ -435,7 +466,6 @@ static void __exit nf_conntrack_l3proto_ipv6_fini(void)
 	nf_ct_l3proto_unregister(&nf_conntrack_l3proto_ipv6);
 	nf_ct_l4proto_unregister(builtin_l4proto6,
 				 ARRAY_SIZE(builtin_l4proto6));
-	nf_unregister_hooks(ipv6_conntrack_ops, ARRAY_SIZE(ipv6_conntrack_ops));
 	unregister_pernet_subsys(&ipv6_net_ops);
 	nf_unregister_sockopt(&so_getorigdst6);
 }