[3.16.y-ckt stable] Patch "mnt: Fail collect_mounts when applied to unmounted mounts" has been added to staging queue

[Luis Henriques]

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

    mnt: Fail collect_mounts when applied to unmounted mounts

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt12.

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

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 4bcf842df09d2cbcd32db82a501383bc6b851fa8 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm at xmission.com>
Date: Wed, 7 Jan 2015 14:28:26 -0600
Subject: mnt: Fail collect_mounts when applied to unmounted mounts

commit cd4a40174b71acd021877341684d8bb1dc8ea4ae upstream.

The only users of collect_mounts are in audit_tree.c

In audit_trim_trees and audit_add_tree_rule the path passed into
collect_mounts is generated from kern_path passed an audit_tree
pathname which is guaranteed to be an absolute path.   In those cases
collect_mounts is obviously intended to work on mounted paths and
if a race results in paths that are unmounted when collect_mounts
it is reasonable to fail early.

The paths passed into audit_tag_tree don't have the absolute path
check.  But are used to play with fsnotify and otherwise interact with
the audit_trees, so again operating only on mounted paths appears
reasonable.

Avoid having to worry about what happens when we try and audit
unmounted filesystems by restricting collect_mounts to mounts
that appear in the mount tree.

Signed-off-by: "Eric W. Biederman" <ebiederm at xmission.com>
Cc: Ben Hutchings <ben at decadent.org.uk>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/namespace.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index d74c67678bb1..0a55bbca650f 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1579,8 +1579,11 @@ struct vfsmount *collect_mounts(struct path *path)
 {
 	struct mount *tree;
 	namespace_lock();
-	tree = copy_tree(real_mount(path->mnt), path->dentry,
-			 CL_COPY_ALL | CL_PRIVATE);
+	if (!check_mnt(real_mount(path->mnt)))
+		tree = ERR_PTR(-EINVAL);
+	else
+		tree = copy_tree(real_mount(path->mnt), path->dentry,
+				 CL_COPY_ALL | CL_PRIVATE);
 	namespace_unlock();
 	if (IS_ERR(tree))
 		return ERR_CAST(tree);