tree 21251b388aec1c09a072ddb489abff447f2c52d6
parent 0e87e58bf60edb6bb28e493c7a143f41b091a5e5
author Andrey Ryabinin <aryabinin@virtuozzo.com> 1471967731 +0300
committer Jens Axboe <axboe@fb.com> 1472135906 -0600

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>