[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>

6 files changed, 83 insertions, 5 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 313c6b6e774f..a4a141055c44 100644
--- a/include/linux/sched.h
+++ b/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
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index ac8f8304094e..3ea4194613ed 100644
--- a/include/net/net_namespace.h
+++ b/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);
diff --git a/kernel/fork.c b/kernel/fork.c
index 33f12f48684a..5e67f90a1694 100644
--- a/kernel/fork.c
+++ b/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)))
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index a4fb7d46971f..f1decd21a534 100644
--- a/kernel/nsproxy.c
+++ b/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))
diff --git a/net/Kconfig b/net/Kconfig
index cdba08ca2efe..ab4e6da5012f 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 0e6cb02d7b77..e478e353ea6b 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;