[NET]: Implement the per network namespace sysctl infrastructure

The user interface is: register_net_sysctl_table and
unregister_net_sysctl_table.  Very much like the current
interface except there is a network namespace parameter.

With this any sysctl registered with register_net_sysctl_table
will only show up to tasks in the same network namespace.

All other sysctls continue to be globally visible.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: Daniel Lezcano <dlezcano@fr.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/net_namespace.h

@@ -25,6 +25,8 @@ struct net {
 	struct proc_dir_entry 	*proc_net_stat;
 	struct proc_dir_entry 	*proc_net_root;
 
+	struct list_head	sysctl_table_headers;
+
 	struct net_device       *loopback_dev;          /* The loopback */
 
 	struct list_head 	dev_base_head;
@@ -144,4 +146,11 @@ extern void unregister_pernet_subsys(struct pernet_operations *);
 extern int register_pernet_device(struct pernet_operations *);
 extern void unregister_pernet_device(struct pernet_operations *);
 
+struct ctl_path;
+struct ctl_table;
+struct ctl_table_header;
+extern struct ctl_table_header *register_net_sysctl_table(struct net *net,
+	const struct ctl_path *path, struct ctl_table *table);
+extern void unregister_net_sysctl_table(struct ctl_table_header *header);
+
 #endif /* __NET_NET_NAMESPACE_H */

net/sysctl_net.c

@@ -14,6 +14,7 @@
 
 #include <linux/mm.h>
 #include <linux/sysctl.h>
+#include <linux/nsproxy.h>
 
 #include <net/sock.h>
 
@@ -54,3 +55,59 @@ struct ctl_table net_table[] = {
 #endif
 	{ 0 },
 };
+
+static struct list_head *
+net_ctl_header_lookup(struct ctl_table_root *root, struct nsproxy *namespaces)
+{
+	return &namespaces->net_ns->sysctl_table_headers;
+}
+
+static struct ctl_table_root net_sysctl_root = {
+	.lookup = net_ctl_header_lookup,
+};
+
+static int sysctl_net_init(struct net *net)
+{
+	INIT_LIST_HEAD(&net->sysctl_table_headers);
+	return 0;
+}
+
+static void sysctl_net_exit(struct net *net)
+{
+	WARN_ON(!list_empty(&net->sysctl_table_headers));
+	return;
+}
+
+static struct pernet_operations sysctl_pernet_ops = {
+	.init = sysctl_net_init,
+	.exit = sysctl_net_exit,
+};
+
+static __init int sysctl_init(void)
+{
+	int ret;
+	ret = register_pernet_subsys(&sysctl_pernet_ops);
+	if (ret)
+		goto out;
+	register_sysctl_root(&net_sysctl_root);
+out:
+	return ret;
+}
+subsys_initcall(sysctl_init);
+
+struct ctl_table_header *register_net_sysctl_table(struct net *net,
+	const struct ctl_path *path, struct ctl_table *table)
+{
+	struct nsproxy namespaces;
+	namespaces = *current->nsproxy;
+	namespaces.net_ns = net;
+	return __register_sysctl_paths(&net_sysctl_root,
+					&namespaces, path, table);
+}
+EXPORT_SYMBOL_GPL(register_net_sysctl_table);
+
+void unregister_net_sysctl_table(struct ctl_table_header *header)
+{
+	return unregister_sysctl_table(header);
+}
+EXPORT_SYMBOL_GPL(unregister_net_sysctl_table);