[PATCH v7 1/3] Staging: zram: Fix access of NULL pointer

From: Rashika Kheria
Date: Tue Oct 29 2013 - 19:11:19 EST

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().

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Rashika Kheria <rashika.kheria@xxxxxxxxx>

This patch fixes the following issues of the previous revision-
Better Description

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

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 2c4ed52..d640a8f 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -648,6 +648,9 @@ static ssize_t reset_store(struct device *dev,
zram = dev_to_zram(dev);
bdev = bdget_disk(zram->disk, 0);

+ if (!bdev)
+ return -EBUSY;
/* Do not reset an active device! */
if (bdev->bd_holders)
return -EBUSY;
@@ -660,8 +663,7 @@ 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);

zram_reset_device(zram, true);
return len;

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