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@redhat.com>
Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
index 1fae1e9..3be52ec 100644 (file)
--- 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)