* [PATCH] fs/block_dev: fix potential NULL ptr deref in freeze_bdev()
@ 2016-08-23 15:55 Andrey Ryabinin
2016-08-25 7:38 ` Christoph Hellwig
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: Andrey Ryabinin @ 2016-08-23 15:55 UTC (permalink / raw)
To: Jens Axboe, Alexander Viro
Cc: linux-fsdevel, Maxim Patlasov, Christoph Hellwig, linux-kernel,
Andrey Ryabinin
Calling freeze_bdev() twice on the same block device without mounted
filesystem get_super() will return NULL, which will lead to NULL-ptr
dereference later in drop_super().
Check get_super() result to fix that.
Note, that this is a purely theoretical issue. We have only 3
freeze_bdev() callers. 2 of them are in filesystem code and used on a
device with mounted fs. The third one in lock_fs() has protection in
upper-layer code against freezing block device the second time without
thawing it first.
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
fs/block_dev.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/block_dev.c b/fs/block_dev.c
index c3cdde8..c18b083 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -249,7 +249,8 @@ struct super_block *freeze_bdev(struct block_device *bdev)
* thaw_bdev drops it.
*/
sb = get_super(bdev);
- drop_super(sb);
+ if (sb)
+ drop_super(sb);
mutex_unlock(&bdev->bd_fsfreeze_mutex);
return sb;
}
--
2.7.3
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] fs/block_dev: fix potential NULL ptr deref in freeze_bdev()
2016-08-23 15:55 [PATCH] fs/block_dev: fix potential NULL ptr deref in freeze_bdev() Andrey Ryabinin
@ 2016-08-25 7:38 ` Christoph Hellwig
2016-08-25 14:38 ` Jens Axboe
2016-08-25 14:39 ` Jens Axboe
2 siblings, 0 replies; 4+ messages in thread
From: Christoph Hellwig @ 2016-08-25 7:38 UTC (permalink / raw)
To: Andrey Ryabinin
Cc: Jens Axboe, Alexander Viro, linux-fsdevel, Maxim Patlasov,
Christoph Hellwig, linux-kernel
On Tue, Aug 23, 2016 at 06:55:31PM +0300, Andrey Ryabinin wrote:
> Calling freeze_bdev() twice on the same block device without mounted
> filesystem get_super() will return NULL, which will lead to NULL-ptr
> dereference later in drop_super().
>
> Check get_super() result to fix that.
>
> Note, that this is a purely theoretical issue. We have only 3
> freeze_bdev() callers. 2 of them are in filesystem code and used on a
> device with mounted fs. The third one in lock_fs() has protection in
> upper-layer code against freezing block device the second time without
> thawing it first.
>
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Looks fine,
Reviewed-by: Christoph Hellwig <hch@lst.de>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] fs/block_dev: fix potential NULL ptr deref in freeze_bdev()
2016-08-23 15:55 [PATCH] fs/block_dev: fix potential NULL ptr deref in freeze_bdev() Andrey Ryabinin
2016-08-25 7:38 ` Christoph Hellwig
@ 2016-08-25 14:38 ` Jens Axboe
2016-08-25 14:39 ` Jens Axboe
2 siblings, 0 replies; 4+ messages in thread
From: Jens Axboe @ 2016-08-25 14:38 UTC (permalink / raw)
To: Andrey Ryabinin, Alexander Viro
Cc: linux-fsdevel, Maxim Patlasov, Christoph Hellwig, linux-kernel
On 08/23/2016 09:55 AM, Andrey Ryabinin wrote:
> Calling freeze_bdev() twice on the same block device without mounted
> filesystem get_super() will return NULL, which will lead to NULL-ptr
> dereference later in drop_super().
>
> Check get_super() result to fix that.
>
> Note, that this is a purely theoretical issue. We have only 3
> freeze_bdev() callers. 2 of them are in filesystem code and used on a
> device with mounted fs. The third one in lock_fs() has protection in
> upper-layer code against freezing block device the second time without
> thawing it first.
Applied, thanks.
--
Jens Axboe
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] fs/block_dev: fix potential NULL ptr deref in freeze_bdev()
2016-08-23 15:55 [PATCH] fs/block_dev: fix potential NULL ptr deref in freeze_bdev() Andrey Ryabinin
2016-08-25 7:38 ` Christoph Hellwig
2016-08-25 14:38 ` Jens Axboe
@ 2016-08-25 14:39 ` Jens Axboe
2 siblings, 0 replies; 4+ messages in thread
From: Jens Axboe @ 2016-08-25 14:39 UTC (permalink / raw)
To: Andrey Ryabinin, Alexander Viro
Cc: linux-fsdevel, Maxim Patlasov, Christoph Hellwig, linux-kernel
On 08/23/2016 09:55 AM, Andrey Ryabinin wrote:
> Calling freeze_bdev() twice on the same block device without mounted
> filesystem get_super() will return NULL, which will lead to NULL-ptr
> dereference later in drop_super().
>
> Check get_super() result to fix that.
>
> Note, that this is a purely theoretical issue. We have only 3
> freeze_bdev() callers. 2 of them are in filesystem code and used on a
> device with mounted fs. The third one in lock_fs() has protection in
> upper-layer code against freezing block device the second time without
> thawing it first.
Applied, thanks.
--
Jens Axboe
^ permalink raw reply [flat|nested] 4+ messages in thread
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2016-08-23 15:55 [PATCH] fs/block_dev: fix potential NULL ptr deref in freeze_bdev() Andrey Ryabinin
2016-08-25 7:38 ` Christoph Hellwig
2016-08-25 14:38 ` Jens Axboe
2016-08-25 14:39 ` Jens Axboe
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