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fs/block_dev: fix potential NULL ptr deref in freeze_bdev() 

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>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Andrey Ryabinin 2016-08-23 18:55:31 +03:00 committed by Jens Axboe
parent 0e87e58bf6
commit 5bb53c0fb8
1 changed files with 2 additions and 1 deletions
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3
fs/block_dev.c
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@ -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;
}