2013-10-29 23:11:10

by Rashika Kheria

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

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: [email protected]
Signed-off-by: Rashika Kheria <[email protected]>
---

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;
--
1.7.9.5

2013-10-30 02:24:26

by Minchan Kim

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

On Wed, Oct 30, 2013 at 04:40:54AM +0530, Rashika Kheria wrote:
> 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: [email protected]
> Signed-off-by: Rashika Kheria <[email protected]>
Acked-by: Minchan Kim <[email protected]>

--
Kind regards,
Minchan Kim

2013-10-30 02:36:23

by Minchan Kim

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

On Wed, Oct 30, 2013 at 04:40:54AM +0530, Rashika Kheria wrote:
> 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: [email protected]
> Signed-off-by: Rashika Kheria <[email protected]>
> ---
>
> 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;
> +

Oops, Sorry.
I don't think EBUSY is right. How about ENOMEM?

--
Kind regards,
Minchan Kim

2013-10-30 10:42:34

by Jerome Marchand

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

On 10/30/2013 12:10 AM, Rashika Kheria wrote:
> 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: [email protected]
> Signed-off-by: Rashika Kheria <[email protected]>
Acked-by: Jerome Marchand <[email protected]>

> ---
>
> 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;
>