[3.11.y.z extended stable] Patch "vfs: Is mounted should be testing mnt_ns for NULL or error." has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 0d42f98074d10ffde10817bcb3d12e084bd20e9c Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm at xmission.com>
Date: Mon, 20 Jan 2014 15:26:15 -0800
Subject: vfs: Is mounted should be testing mnt_ns for NULL or error.

commit 260a459d2e39761fbd39803497205ce1690bc7b1 upstream.

A bug was introduced with the is_mounted helper function in
commit f7a99c5b7c8bd3d3f533c8b38274e33f3da9096e
Author: Al Viro <viro at 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 at 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 at xmission.com>
Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/mount.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/mount.h b/fs/mount.h
index 64a8581..68d80bd 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -73,7 +73,7 @@ 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