[3.5.y.z extended stable] Patch "Staging: zram: Fix access of NULL pointer" has been added to staging queue

[Luis Henriques]

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

    Staging: zram: Fix access of NULL pointer

to the linux-3.5.y-queue branch of the 3.5.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-3.5.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 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From c21e1d9bb775b9e58222b84d9735d6e68a9de3d2 Mon Sep 17 00:00:00 2001
From: Rashika Kheria <rashika.kheria at gmail.com>
Date: Wed, 30 Oct 2013 18:36:32 +0530
Subject: Staging: zram: Fix access of NULL pointer

commit 46a51c80216cb891f271ad021f59009f34677499 upstream.

This patch fixes the bug in reset_store caused by accessing NULL pointer.

The bdev gets its value from bdget_disk() which could fail when memory
pressure is severe and hence can return NULL because allocation of
inode in bdget could fail.

Hence, this patch introduces a check for bdev to prevent reference to a
NULL pointer in the later part of the code. It also removes unnecessary
check of bdev for fsync_bdev().

Acked-by: Jerome Marchand <jmarchan at redhat.com>
Signed-off-by: Rashika Kheria <rashika.kheria at gmail.com>
Acked-by: Minchan Kim <minchan at kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
[ luis: backported to 3.5:
  - adjusted filename: zram_drv.c -> zram_sysfs.c ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/staging/zram/zram_sysfs.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
index dbe8907..01f9a79 100644
--- a/drivers/staging/zram/zram_sysfs.c
+++ b/drivers/staging/zram/zram_sysfs.c
@@ -95,6 +95,9 @@ static ssize_t reset_store(struct device *dev,
 	zram = dev_to_zram(dev);
 	bdev = bdget_disk(zram->disk, 0);

+	if (!bdev)
+		return -ENOMEM;
+
 	/* Do not reset an active device! */
 	if (bdev->bd_holders)
 		return -EBUSY;
@@ -107,8 +110,7 @@ static ssize_t reset_store(struct device *dev,
 		return -EINVAL;

 	/* Make sure all pending I/O is finished */
-	if (bdev)
-		fsync_bdev(bdev);
+	fsync_bdev(bdev);

 	down_write(&zram->init_lock);
 	if (zram->init_done)
--
1.8.3.2