vfs: Is mounted should be testing mnt_ns for NULL or error.

A bug was introduced with the is_mounted helper function in commit f7a99c5b7c8bd3d3f533c8b38274e33f3da9096e

Author: Al Viro <[email protected]>
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 <[email protected]>

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.

---
 fs/mount.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index d64c594be6c4..a17458ca6f29 100644
@@ -74,7 +74,7 @@ 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 *);

1.7.5.4