Hi,
在 2024/11/06 11:11, Ming Lei 写道:
On Wed, Nov 06, 2024 at 10:58:40AM +0800, Yu Kuai wrote:
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.
How can that be one problem?
Please look at
commit 364b61818f65 ("blk-mq: clearing flush request reference in tags->rqs[]")
commit bd63141d585b ("blk-mq: clear stale request in tags->rq[] before freeing one request pool")
and understand the motivation.
That also means it is just fine to delay blk_mq_clear_flush_rq_mapping()
after disk is deleted.
I do understand what you mean. Let's see if you want this to be avoided,
for example(no disk is deleted):
1) issue a flush, and tag 0 is used, after the flush is done,
tags->rqs[0] = flush_rq
2) issue another flush, and tag 1 is used, after the flush is done,
tags->rqs[1] = flush_rq
3) issue a flush again, and tag 2 is used, and the flush_rq is
dispatched to disk;
4) Then in this case, blk_mq_in_flight_rw() will found the same flush_rq
3 times and think there are 3 inflight request, same for
hctx_busy_show()...
Thanks,
Kuai
Thanks,
Ming
.
