Hi,Ming and Christoph 在 2024/11/05 19:19, Christoph Hellwig 写道:
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.
This remind me that del_gendisk is still too late to do that. Noted that flush_rq can acquire different tags, so if the multiple flush_rq is done and those tags are not reused, the flush_rq can exist in multiple entries in tags->rqs[]. The consequence I can think of is that iterating tags can found the same flush_rq multiple times, and the flush_rq can be inflight. Therefor, I think the best solution is to clear the flush_rq mapping when flush request is done. Thanks, Kuai
.
