[NET]: Add network namespace clone & unshare support.

This patch allows you to create a new network namespace
using sys_clone, or sys_unshare.

As the network namespace is still experimental and under development
clone and unshare support is only made available when CONFIG_NET_NS is
selected at compile time.

As this patch introduces network namespace support into code paths
that exist when the CONFIG_NET is not selected there are a few
additions made to net_namespace.h to allow a few more functions
to be used when the networking stack is not compiled in.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 49 insertions, 2 deletions

diff --git a/net/Kconfig b/net/Kconfig
index cdba08ca2ef..ab4e6da5012 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -27,6 +27,14 @@ if NET
 
 menu "Networking options"
 
+config NET_NS
+	bool "Network namespace support"
+	default n
+	depends on EXPERIMENTAL && !SYSFS
+	help
+	  Allow user space to create what appear to be multiple instances
+	  of the network stack.
+
 source "net/packet/Kconfig"
 source "net/unix/Kconfig"
 source "net/xfrm/Kconfig"
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 0e6cb02d7b7..e478e353ea6 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -4,6 +4,7 @@
 #include <linux/slab.h>
 #include <linux/list.h>
 #include <linux/delay.h>
+#include <linux/sched.h>
 #include <net/net_namespace.h>
 
 /*
@@ -32,12 +33,10 @@ void net_unlock(void)
 	mutex_unlock(&net_list_mutex);
 }
 
-#if 0
 static struct net *net_alloc(void)
 {
 	return kmem_cache_alloc(net_cachep, GFP_KERNEL);
 }
-#endif
 
 static void net_free(struct net *net)
 {
@@ -128,6 +127,46 @@ out_undo:
 	goto out;
 }
 
+struct net *copy_net_ns(unsigned long flags, struct net *old_net)
+{
+	struct net *new_net = NULL;
+	int err;
+
+	get_net(old_net);
+
+	if (!(flags & CLONE_NEWNET))
+		return old_net;
+
+#ifndef CONFIG_NET_NS
+	return ERR_PTR(-EINVAL);
+#endif
+
+	err = -ENOMEM;
+	new_net = net_alloc();
+	if (!new_net)
+		goto out;
+
+	mutex_lock(&net_mutex);
+	err = setup_net(new_net);
+	if (err)
+		goto out_unlock;
+
+	net_lock();
+	list_add_tail(&new_net->list, &net_namespace_list);
+	net_unlock();
+
+
+out_unlock:
+	mutex_unlock(&net_mutex);
+out:
+	put_net(old_net);
+	if (err) {
+		net_free(new_net);
+		new_net = ERR_PTR(err);
+	}
+	return new_net;
+}
+
 static int __init net_ns_init(void)
 {
 	int err;