2014-10-25 19:37:21

by Weijie Yang

Subject: [PATCH 2/2] zram: avoid NULL pointer access when reading mem_used_total

There is a rare NULL pointer bug in mem_used_total_show() in concurrent
situation, like this:
zram is not initialized, process A is a mem_used_total reader which runs
periodicity, while process B try to init zram.

process A process B
access meta, get a NULL value
init zram, done
init_done() is true
access meta->mem_pool, get a NULL pointer BUG

This patch fixes this issue.

Signed-off-by: Weijie Yang <[email protected]>
---
drivers/block/zram/zram_drv.c | 5 +++--
1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 64dd79a..2ffd7d8 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -99,11 +99,12 @@ static ssize_t mem_used_total_show(struct device *dev,
{
u64 val = 0;
struct zram *zram = dev_to_zram(dev);
- struct zram_meta *meta = zram->meta;

down_read(&zram->init_lock);
- if (init_done(zram))
+ if (init_done(zram)) {
+ struct zram_meta *meta = zram->meta;
val = zs_get_total_pages(meta->mem_pool);
+ }
up_read(&zram->init_lock);

return scnprintf(buf, PAGE_SIZE, "%llu\n", val << PAGE_SHIFT);
--
1.7.0.4

2014-10-26 01:45:00

by Minchan Kim

Subject: Re: [PATCH 2/2] zram: avoid NULL pointer access when reading mem_used_total

On Sat, Oct 25, 2014 at 05:26:31PM +0800, Weijie Yang wrote:
> There is a rare NULL pointer bug in mem_used_total_show() in concurrent
> situation, like this:
> zram is not initialized, process A is a mem_used_total reader which runs
> periodicity, while process B try to init zram.
>
> process A process B
> access meta, get a NULL value
> init zram, done
> init_done() is true
> access meta->mem_pool, get a NULL pointer BUG
>
> This patch fixes this issue.
>
> Signed-off-by: Weijie Yang <[email protected]>
Acked-by: Minchan Kim <[email protected]>

Thanks!

--
Kind regards,
Minchan Kim

2014-10-26 05:41:18

by Sergey Senozhatsky

Subject: Re: [PATCH 2/2] zram: avoid NULL pointer access when reading mem_used_total

On (10/25/14 17:26), Weijie Yang wrote:
> Date: Sat, 25 Oct 2014 17:26:31 +0800
> From: Weijie Yang <[email protected]>
> To: 'Minchan Kim' <[email protected]>
> Cc: 'Andrew Morton' <[email protected]>, 'Dan Streetman'
> <[email protected]>, 'Sergey Senozhatsky' <[email protected]>,
> 'Nitin Gupta' <[email protected]>, 'Linux-MM' <[email protected]>,
> 'linux-kernel' <[email protected]>, 'Weijie Yang'
> <[email protected]>
> Subject: [PATCH 2/2] zram: avoid NULL pointer access when reading
> mem_used_total
> X-Mailer: Microsoft Office Outlook 12.0
>
> There is a rare NULL pointer bug in mem_used_total_show() in concurrent
> situation, like this:
> zram is not initialized, process A is a mem_used_total reader which runs
> periodicity, while process B try to init zram.
>
> process A process B
> access meta, get a NULL value
> init zram, done
> init_done() is true
> access meta->mem_pool, get a NULL pointer BUG
>
> This patch fixes this issue.
>
> Signed-off-by: Weijie Yang <[email protected]>

Acked-by: Sergey Senozhatsky <[email protected]>

-ss

> ---
> drivers/block/zram/zram_drv.c | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 64dd79a..2ffd7d8 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -99,11 +99,12 @@ static ssize_t mem_used_total_show(struct device *dev,
> {
> u64 val = 0;
> struct zram *zram = dev_to_zram(dev);
> - struct zram_meta *meta = zram->meta;
>
> down_read(&zram->init_lock);
> - if (init_done(zram))
> + if (init_done(zram)) {
> + struct zram_meta *meta = zram->meta;
> val = zs_get_total_pages(meta->mem_pool);
> + }
> up_read(&zram->init_lock);
>
> return scnprintf(buf, PAGE_SIZE, "%llu\n", val << PAGE_SHIFT);
> --
> 1.7.0.4
>
>