[PATCH] unshare system call -v5: unshare namespace

If the namespace structure is being shared, allocate a new one and copy
information from the current, shared, structure.

Signed-off-by: Janak Desai <janak@us.ibm.com>
Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Cc: Andi Kleen <ak@muc.de>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 48 insertions, 26 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index ce97becff461..a2bef5c81033 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1325,27 +1325,17 @@ dput_out:
         return retval;
 }
 
-int copy_namespace(int flags, struct task_struct *tsk)
+/*
+ * Allocate a new namespace structure and populate it with contents
+ * copied from the namespace of the passed in task structure.
+ */
+struct namespace *dup_namespace(struct task_struct *tsk, struct fs_struct *fs)
 {
         struct namespace *namespace = tsk->namespace;
         struct namespace *new_ns;
         struct vfsmount *rootmnt = NULL, *pwdmnt = NULL, *altrootmnt = NULL;
-        struct fs_struct *fs = tsk->fs;
         struct vfsmount *p, *q;
 
-        if (!namespace)
-                return 0;
-
-        get_namespace(namespace);
-
-        if (!(flags & CLONE_NEWNS))
-                return 0;
-
-        if (!capable(CAP_SYS_ADMIN)) {
-                put_namespace(namespace);
-                return -EPERM;
-        }
-
         new_ns = kmalloc(sizeof(struct namespace), GFP_KERNEL);
         if (!new_ns)
                 goto out;
@@ -1396,8 +1386,6 @@ int copy_namespace(int flags, struct task_struct *tsk)
         }
         up_write(&namespace_sem);
 
-        tsk->namespace = new_ns;
-
         if (rootmnt)
                 mntput(rootmnt);
         if (pwdmnt)
@@ -1405,12 +1393,40 @@ int copy_namespace(int flags, struct task_struct *tsk)
         if (altrootmnt)
                 mntput(altrootmnt);
 
-        put_namespace(namespace);
-        return 0;
+out:
+        return new_ns;
+}
+
+int copy_namespace(int flags, struct task_struct *tsk)
+{
+        struct namespace *namespace = tsk->namespace;
+        struct namespace *new_ns;
+        int err = 0;
+
+        if (!namespace)
+                return 0;
+
+        get_namespace(namespace);
+
+        if (!(flags & CLONE_NEWNS))
+                return 0;
+
+        if (!capable(CAP_SYS_ADMIN)) {
+                err = -EPERM;
+                goto out;
+        }
+
+        new_ns = dup_namespace(tsk, tsk->fs);
+        if (!new_ns) {
+                err = -ENOMEM;
+                goto out;
+        }
+
+        tsk->namespace = new_ns;
 
 out:
         put_namespace(namespace);
-        return -ENOMEM;
+        return err;
 }
 
 asmlinkage long sys_mount(char __user * dev_name, char __user * dir_name,
diff --git a/include/linux/namespace.h b/include/linux/namespace.h
index 6731977c4c13..3abc8e3b4879 100644
--- a/include/linux/namespace.h
+++ b/include/linux/namespace.h
@@ -15,6 +15,7 @@ struct namespace {
 
 extern int copy_namespace(int, struct task_struct *);
 extern void __put_namespace(struct namespace *namespace);
+extern struct namespace *dup_namespace(struct task_struct *, struct fs_struct *);
 
 static inline void put_namespace(struct namespace *namespace)
 {
diff --git a/kernel/fork.c b/kernel/fork.c
index 598e5c27242c..07dd241aa1e0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1388,16 +1388,21 @@ static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
 }
 
 /*
- * Unsharing of namespace for tasks created without CLONE_NEWNS is not
- * supported yet
+ * Unshare the namespace structure if it is being shared
  */
-static int unshare_namespace(unsigned long unshare_flags, struct namespace **new_nsp)
+static int unshare_namespace(unsigned long unshare_flags, struct namespace **new_nsp, struct fs_struct *new_fs)
 {
         struct namespace *ns = current->namespace;
 
         if ((unshare_flags & CLONE_NEWNS) &&
-            (ns && atomic_read(&ns->count) > 1))
-                return -EINVAL;
+            (ns && atomic_read(&ns->count) > 1)) {
+                if (!capable(CAP_SYS_ADMIN))
+                        return -EPERM;
+
+                *new_nsp = dup_namespace(current, new_fs ? new_fs : current->fs);
+                if (!*new_nsp)
+                        return -ENOMEM;
+        }
 
         return 0;
 }
@@ -1482,7 +1487,7 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
                 goto bad_unshare_out;
         if ((err = unshare_fs(unshare_flags, &new_fs)))
                 goto bad_unshare_cleanup_thread;
-        if ((err = unshare_namespace(unshare_flags, &new_ns)))
+        if ((err = unshare_namespace(unshare_flags, &new_ns, new_fs)))
                 goto bad_unshare_cleanup_fs;
         if ((err = unshare_sighand(unshare_flags, &new_sigh)))
                 goto bad_unshare_cleanup_ns;