netfilter: conntrack: do not enable connection tracking unless needed

Discussion during NFWS 2017 in Faro has shown that the current
conntrack behaviour is unreasonable.

Even if conntrack module is loaded on behalf of a single net namespace,
its turned on for all namespaces, which is expensive.  Commit
481fa373476 ("netfilter: conntrack: add nf_conntrack_default_on sysctl")
attempted to provide an alternative to the 'default on' behaviour by
adding a sysctl to change it.

However, as Eric points out, the sysctl only becomes available
once the module is loaded, and then its too late.

So we either have to move the sysctl to the core, or, alternatively,
change conntrack to become active only once the rule set requires this.

This does the latter, conntrack is only enabled when a rule needs it.

Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

4 files changed, 4 insertions, 68 deletions

diff --git a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
index 63e4ea0e01f8..de5f0e6ddd1b 100644
--- a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
+++ b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
@@ -398,24 +398,12 @@ static struct nf_conntrack_l4proto *builtin_l4proto4[] = {
 
 static int ipv4_net_init(struct net *net)
 {
-	int ret = 0;
-
-	ret = nf_ct_l4proto_pernet_register(net, builtin_l4proto4,
-					    ARRAY_SIZE(builtin_l4proto4));
-	if (ret < 0)
-		return ret;
-	ret = nf_ct_l3proto_pernet_register(net, &nf_conntrack_l3proto_ipv4);
-	if (ret < 0) {
-		pr_err("nf_conntrack_ipv4: pernet registration failed\n");
-		nf_ct_l4proto_pernet_unregister(net, builtin_l4proto4,
-						ARRAY_SIZE(builtin_l4proto4));
-	}
-	return ret;
+	return nf_ct_l4proto_pernet_register(net, builtin_l4proto4,
+					     ARRAY_SIZE(builtin_l4proto4));
 }
 
 static void ipv4_net_exit(struct net *net)
 {
-	nf_ct_l3proto_pernet_unregister(net, &nf_conntrack_l3proto_ipv4);
 	nf_ct_l4proto_pernet_unregister(net, builtin_l4proto4,
 					ARRAY_SIZE(builtin_l4proto4));
 }
diff --git a/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c b/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
index f2d2f4a9294b..ddef5ee9e0a8 100644
--- a/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
+++ b/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
@@ -398,25 +398,12 @@ static struct nf_conntrack_l4proto *builtin_l4proto6[] = {
 
 static int ipv6_net_init(struct net *net)
 {
-	int ret = 0;
-
-	ret = nf_ct_l4proto_pernet_register(net, builtin_l4proto6,
-					    ARRAY_SIZE(builtin_l4proto6));
-	if (ret < 0)
-		return ret;
-
-	ret = nf_ct_l3proto_pernet_register(net, &nf_conntrack_l3proto_ipv6);
-	if (ret < 0) {
-		pr_err("nf_conntrack_ipv6: pernet registration failed.\n");
-		nf_ct_l4proto_pernet_unregister(net, builtin_l4proto6,
-						ARRAY_SIZE(builtin_l4proto6));
-	}
-	return ret;
+	return nf_ct_l4proto_pernet_register(net, builtin_l4proto6,
+					     ARRAY_SIZE(builtin_l4proto6));
 }
 
 static void ipv6_net_exit(struct net *net)
 {
-	nf_ct_l3proto_pernet_unregister(net, &nf_conntrack_l3proto_ipv6);
 	nf_ct_l4proto_pernet_unregister(net, builtin_l4proto6,
 					ARRAY_SIZE(builtin_l4proto6));
 }
diff --git a/net/netfilter/nf_conntrack_proto.c b/net/netfilter/nf_conntrack_proto.c
index 1dcad229c3cc..7c89dade6fd3 100644
--- a/net/netfilter/nf_conntrack_proto.c
+++ b/net/netfilter/nf_conntrack_proto.c
@@ -238,20 +238,6 @@ out_unlock:
 }
 EXPORT_SYMBOL_GPL(nf_ct_l3proto_register);
 
-#ifdef CONFIG_SYSCTL
-extern unsigned int nf_conntrack_default_on;
-
-int nf_ct_l3proto_pernet_register(struct net *net,
-				  struct nf_conntrack_l3proto *proto)
-{
-	if (nf_conntrack_default_on == 0)
-		return 0;
-
-	return proto->net_ns_get ? proto->net_ns_get(net) : 0;
-}
-EXPORT_SYMBOL_GPL(nf_ct_l3proto_pernet_register);
-#endif
-
 void nf_ct_l3proto_unregister(struct nf_conntrack_l3proto *proto)
 {
 	BUG_ON(proto->l3proto >= NFPROTO_NUMPROTO);
@@ -270,21 +256,6 @@ void nf_ct_l3proto_unregister(struct nf_conntrack_l3proto *proto)
 }
 EXPORT_SYMBOL_GPL(nf_ct_l3proto_unregister);
 
-void nf_ct_l3proto_pernet_unregister(struct net *net,
-				     struct nf_conntrack_l3proto *proto)
-{
-	/*
-	 * nf_conntrack_default_on *might* have registered hooks.
-	 * ->net_ns_put must cope with more puts() than get(), i.e.
-	 * if nf_conntrack_default_on was 0 at time of
-	 * nf_ct_l3proto_pernet_register invocation this net_ns_put()
-	 * should be a noop.
-	 */
-	if (proto->net_ns_put)
-		proto->net_ns_put(net);
-}
-EXPORT_SYMBOL_GPL(nf_ct_l3proto_pernet_unregister);
-
 static struct nf_proto_net *nf_ct_l4proto_net(struct net *net,
 					      struct nf_conntrack_l4proto *l4proto)
 {
diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index ccb5cb9043e0..5b6c675d55b1 100644
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -452,9 +452,6 @@ static int log_invalid_proto_max __read_mostly = 255;
 /* size the user *wants to set */
 static unsigned int nf_conntrack_htable_size_user __read_mostly;
 
-extern unsigned int nf_conntrack_default_on;
-unsigned int nf_conntrack_default_on __read_mostly = 1;
-
 static int
 nf_conntrack_hash_sysctl(struct ctl_table *table, int write,
 			 void __user *buffer, size_t *lenp, loff_t *ppos)
@@ -520,13 +517,6 @@ static struct ctl_table nf_ct_sysctl_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
-	{
-		.procname	= "nf_conntrack_default_on",
-		.data		= &nf_conntrack_default_on,
-		.maxlen		= sizeof(unsigned int),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
-	},
 	{ }
 };