5 files changed, 54 insertions, 4 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index c667255d70db..731edaca8ffd 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -26,6 +26,7 @@
 #define CLONE_STOPPED           0x02000000      /* Start in stopped state */
 #define CLONE_NEWUTS            0x04000000      /* New utsname group? */
 #define CLONE_NEWIPC            0x08000000      /* New ipcs */
+#define CLONE_NEWUSER           0x10000000      /* New user namespace */
 
 /*
  * Scheduling policies
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 92a45867ecfb..bb320573bb9e 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -4,6 +4,7 @@
 #include <linux/kref.h>
 #include <linux/nsproxy.h>
 #include <linux/sched.h>
+#include <linux/err.h>
 
 #define UIDHASH_BITS    (CONFIG_BASE_SMALL ? 3 : 8)
 #define UIDHASH_SZ      (1 << UIDHASH_BITS)
@@ -45,6 +46,9 @@ static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
 static inline struct user_namespace *copy_user_ns(int flags,
                                                   struct user_namespace *old_ns)
 {
+        if (flags & CLONE_NEWUSER)
+                return ERR_PTR(-EINVAL);
+
         return NULL;
 }
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 13cf0978780a..7c5c5888e00a 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1606,7 +1606,7 @@ 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_NEWUTS|CLONE_NEWIPC|CLONE_NEWUSER))
                 goto bad_unshare_out;
 
         if ((err = unshare_thread(unshare_flags)))
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 895e3a3f2044..5aa28e219487 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -117,7 +117,7 @@ int copy_namespaces(int flags, struct task_struct *tsk)
 
         get_nsproxy(old_ns);
 
-        if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC)))
+        if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC | CLONE_NEWUSER)))
                 return 0;
 
         if (!capable(CAP_SYS_ADMIN)) {
@@ -161,7 +161,8 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags,
 {
         int err = 0;
 
-        if (!(unshare_flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC)))
+        if (!(unshare_flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
+                               CLONE_NEWUSER)))
                 return 0;
 
         if (!capable(CAP_SYS_ADMIN))
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 3d7964209774..89a27e8b17fb 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -21,6 +21,45 @@ EXPORT_SYMBOL_GPL(init_user_ns);
 
 #ifdef CONFIG_USER_NS
 
+/*
+ * Clone a new ns copying an original user ns, setting refcount to 1
+ * @old_ns: namespace to clone
+ * Return NULL on error (failure to kmalloc), new ns otherwise
+ */
+static struct user_namespace *clone_user_ns(struct user_namespace *old_ns)
+{
+        struct user_namespace *ns;
+        struct user_struct *new_user;
+        int n;
+
+        ns = kmalloc(sizeof(struct user_namespace), GFP_KERNEL);
+        if (!ns)
+                return NULL;
+
+        kref_init(&ns->kref);
+
+        for (n = 0; n < UIDHASH_SZ; ++n)
+                INIT_LIST_HEAD(ns->uidhash_table + n);
+
+        /* Insert new root user.  */
+        ns->root_user = alloc_uid(ns, 0);
+        if (!ns->root_user) {
+                kfree(ns);
+                return NULL;
+        }
+
+        /* Reset current->user with a new one */
+        new_user = alloc_uid(ns, current->uid);
+        if (!new_user) {
+                free_uid(ns->root_user);
+                kfree(ns);
+                return NULL;
+        }
+
+        switch_uid(new_user);
+        return ns;
+}
+
 struct user_namespace * copy_user_ns(int flags, struct user_namespace *old_ns)
 {
         struct user_namespace *new_ns;
@@ -28,7 +67,12 @@ struct user_namespace * copy_user_ns(int flags, struct user_namespace *old_ns)
         BUG_ON(!old_ns);
         get_user_ns(old_ns);
 
-        new_ns = old_ns;
+        if (!(flags & CLONE_NEWUSER))
+                return old_ns;
+
+        new_ns = clone_user_ns(old_ns);
+
+        put_user_ns(old_ns);
         return new_ns;
 }