Re: [PATCH -next] block: fix uaf for flush rq while iterating tags

[Christoph Hellwig]

On Mon, Nov 04, 2024 at 07:00:05PM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
> 
> blk_mq_clear_flush_rq_mapping() is not called during scsi probe, by
> checking blk_queue_init_done(). However, QUEUE_FLAG_INIT_DONE is cleared
> in del_gendisk by commit aec89dc5d421 ("block: keep q_usage_counter in
> atomic mode after del_gendisk"), hence for disk like scsi, following
> blk_mq_destroy_queue() will not clear flush rq from tags->rqs[] as well,
> cause following uaf that is found by our syzkaller for v6.6:

Which means we leave the flush request lingering after del_gendisk,
which sounds like the real bug.  I suspect we just need to move the
call to blk_mq_clear_flush_rq_mapping so that it is called from
del_gendisk and doesn't leave the flush tag lingering around.