[3.16.y-ckt stable] Patch "mnt: Fix fs_fully_visible to verify the root directory is visible" 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: Fix fs_fully_visible to verify the root directory is visible

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 63d525e671b09a4fc6639b583491e27191c04655 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm at xmission.com>
Date: Fri, 8 May 2015 16:36:50 -0500
Subject: mnt: Fix fs_fully_visible to verify the root directory is visible

commit 7e96c1b0e0f495c5a7450dc4aa7c9a24ba4305bd upstream.

This fixes a dumb bug in fs_fully_visible that allows proc or sys to
be mounted if there is a bind mount of part of /proc/ or /sys/ visible.

Reported-by: Eric Windisch <ewindisch at docker.com>
Signed-off-by: "Eric W. Biederman" <ebiederm at xmission.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/namespace.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index 0a55bbca650f..6dfb6fc34286 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3038,6 +3038,12 @@ bool fs_fully_visible(struct file_system_type *type)
 		if (mnt->mnt.mnt_sb->s_type != type)
 			continue;

+		/* This mount is not fully visible if it's root directory
+		 * is not the root directory of the filesystem.
+		 */
+		if (mnt->mnt.mnt_root != mnt->mnt.mnt_sb->s_root)
+			continue;
+
 		/* This mount is not fully visible if there are any child mounts
 		 * that cover anything except for empty directories.
 		 */