[PATCH 3.4 107/214] Staging: zram: Fix access of NULL pointer

From: Greg Kroah-Hartman
Date: Thu Jun 05 2014 - 00:52:25 EST

3.4-stable review patch. If anyone has any objections, please let me know.


From: Rashika Kheria <rashika.kheria@xxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Rashika Kheria <rashika.kheria@xxxxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Cc: Jianguo Wu <wujianguo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/staging/zram/zram_sysfs.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- 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
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
return -EINVAL;

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

if (zram->init_done)

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