[PATCH 3.8 091/124] vfs: Is mounted should be testing mnt_ns for NULL or error.

[Kamal Mostafa <kamal@canonical.com>]

3.8.13.18 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Eric W. Biederman" <ebiederm@xmission.com>

commit 260a459d2e39761fbd39803497205ce1690bc7b1 upstream.

A bug was introduced with the is_mounted helper function in
commit f7a99c5b7c8bd3d3f533c8b38274e33f3da9096e
Author: Al Viro <viro@zeniv.linux.org.uk>
Date:   Sat Jun 9 00:59:08 2012 -0400

    get rid of ->mnt_longterm

    it's enough to set ->mnt_ns of internal vfsmounts to something
    distinct from all struct mnt_namespace out there; then we can
    just use the check for ->mnt_ns != NULL in the fast path of
    mntput_no_expire()

    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

The intent was to test if the real_mount(vfsmount)->mnt_ns was
NULL_OR_ERR but the code is actually testing real_mount(vfsmount)
and always returning true.

The result is d_absolute_path returning paths it should be hiding.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 fs/mount.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/mount.h b/fs/mount.h
index cd50079..f58a3ab 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -66,7 +66,7 @@ static inline int mnt_has_parent(struct mount *mnt)
 static inline int is_mounted(struct vfsmount *mnt)
 {
 	/* neither detached nor internal? */
-	return !IS_ERR_OR_NULL(real_mount(mnt));
+	return !IS_ERR_OR_NULL(real_mount(mnt)->mnt_ns);
 }
 
 extern struct mount *__lookup_mnt(struct vfsmount *, struct dentry *, int);
-- 
1.8.3.2