mnt: Carefully set CL_UNPRIVILEGED in clone_mnt

old->mnt_expiry should be ignored unless CL_EXPIRE is set.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

fs/namespace.c

@@ -963,7 +963,8 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root,
 	}
 
 	/* Don't allow unprivileged users to reveal what is under a mount */
-	if ((flag & CL_UNPRIVILEGED) && list_empty(&old->mnt_expire))
+	if ((flag & CL_UNPRIVILEGED) &&
+	    (!(flag & CL_EXPIRE) || list_empty(&old->mnt_expire)))
 		mnt->mnt.mnt_flags |= MNT_LOCKED;
 
 	atomic_inc(&sb->s_active);