[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>

include/linux/sched.h

@@ -27,6 +27,7 @@
 #define CLONE_NEWUTS		0x04000000	/* New utsname group? */
 #define CLONE_NEWIPC		0x08000000	/* New ipcs */
 #define CLONE_NEWUSER		0x10000000	/* New user namespace */
+#define CLONE_NEWNET		0x20000000	/* New network namespace */
 
 /*
  * Scheduling policies

include/net/net_namespace.h

@@ -38,11 +38,23 @@ extern struct net init_net;
 
 extern struct list_head net_namespace_list;
 
+#ifdef CONFIG_NET
+extern struct net *copy_net_ns(unsigned long flags, struct net *net_ns);
+#else
+static inline struct net *copy_net_ns(unsigned long flags, struct net *net_ns)
+{
+	/* There is nothing to copy so this is a noop */
+	return net_ns;
+}
+#endif
+
 extern void __put_net(struct net *net);
 
 static inline struct net *get_net(struct net *net)
 {
+#ifdef CONFIG_NET
 	atomic_inc(&net->count);
+#endif
 	return net;
 }
 
@@ -60,19 +72,25 @@ static inline struct net *maybe_get_net(struct net *net)
 
 static inline void put_net(struct net *net)
 {
+#ifdef CONFIG_NET
 	if (atomic_dec_and_test(&net->count))
 		__put_net(net);
+#endif
 }
 
 static inline struct net *hold_net(struct net *net)
 {
+#ifdef CONFIG_NET
 	atomic_inc(&net->use_count);
+#endif
 	return net;
 }
 
 static inline void release_net(struct net *net)
 {
+#ifdef CONFIG_NET
 	atomic_dec(&net->use_count);
+#endif
 }
 
 extern void net_lock(void);

kernel/fork.c

@@ -1608,7 +1608,8 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
 	err = -EINVAL;
 	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
 				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
-				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWUSER))
+				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWUSER|
+				CLONE_NEWNET))
 		goto bad_unshare_out;
 
 	if ((err = unshare_thread(unshare_flags)))

kernel/nsproxy.c

@@ -20,6 +20,7 @@
 #include <linux/mnt_namespace.h>
 #include <linux/utsname.h>
 #include <linux/pid_namespace.h>
+#include <net/net_namespace.h>
 
 static struct kmem_cache *nsproxy_cachep;
 
@@ -98,8 +99,17 @@ static struct nsproxy *create_new_namespaces(unsigned long flags,
 		goto out_user;
 	}
 
+	new_nsp->net_ns = copy_net_ns(flags, tsk->nsproxy->net_ns);
+	if (IS_ERR(new_nsp->net_ns)) {
+		err = PTR_ERR(new_nsp->net_ns);
+		goto out_net;
+	}
+
 	return new_nsp;
 
+out_net:
+	if (new_nsp->user_ns)
+		put_user_ns(new_nsp->user_ns);
 out_user:
 	if (new_nsp->pid_ns)
 		put_pid_ns(new_nsp->pid_ns);
@@ -132,7 +142,7 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
 
 	get_nsproxy(old_ns);
 
-	if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC | CLONE_NEWUSER)))
+	if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC | CLONE_NEWUSER | CLONE_NEWNET)))
 		return 0;
 
 	if (!capable(CAP_SYS_ADMIN)) {
@@ -164,6 +174,7 @@ void free_nsproxy(struct nsproxy *ns)
 		put_pid_ns(ns->pid_ns);
 	if (ns->user_ns)
 		put_user_ns(ns->user_ns);
+	put_net(ns->net_ns);
 	kmem_cache_free(nsproxy_cachep, ns);
 }
 
@@ -177,7 +188,7 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags,
 	int err = 0;
 
 	if (!(unshare_flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
-			       CLONE_NEWUSER)))
+			       CLONE_NEWUSER | CLONE_NEWNET)))
 		return 0;
 
 	if (!capable(CAP_SYS_ADMIN))

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"

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;