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

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Message-ID: <217f242b-b4e2-89f7-3b0f-3337c251a603@huaweicloud.com>
Date: Wed, 6 Nov 2024 10:58:40 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Christoph Hellwig <hch@...radead.org>, Yu Kuai <yukuai1@...weicloud.com>
Cc: axboe@...nel.dk, ming.lei@...hat.com, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, yi.zhang@...wei.com, yangerkun@...wei.com,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -next] block: fix uaf for flush rq while iterating tags

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@...wei.com>
>>
>> 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
> .
>