From: Christoph Hellwig <hch@infradead.org>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, Bart Van Assche <bvanassche@acm.org>,
Hannes Reinecke <hare@suse.de>,
John Garry <john.garry@huawei.com>,
David Jeffery <djeffery@redhat.com>
Subject: Re: [PATCH V5 2/4] blk-mq: grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter
Date: Thu, 6 May 2021 07:54:40 +0100 [thread overview]
Message-ID: <20210506065440.GC328487@infradead.org> (raw)
In-Reply-To: <20210505145855.174127-3-ming.lei@redhat.com>
On Wed, May 05, 2021 at 10:58:53PM +0800, Ming Lei wrote:
> Grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter(), and
> this way will prevent the request from being re-used when ->fn is
> running. The approach is same as what we do during handling timeout.
>
> Fix request UAF related with completion race or queue releasing:
I guess UAF is supposed to mean use-after-free? Please just spell that
out.
> + rq = blk_mq_find_and_get_req(tags, bitnr);
> /*
> * We can hit rq == NULL here, because the tagging functions
> * test and set the bit before assigning ->rqs[].
> */
> + if (!rq)
> + return true;
Nit: I'd find this much earier to follow if the blk_mq_find_and_get_req
and thus assignment to rq was after the block comment.
> struct blk_mq_tags *tags = iter_data->tags;
> bool reserved = iter_data->flags & BT_TAG_ITER_RESERVED;
> struct request *rq;
> + bool ret = true;
> + bool iter_static_rqs = !!(iter_data->flags & BT_TAG_ITER_STATIC_RQS);
>
> if (!reserved)
> bitnr += tags->nr_reserved_tags;
> @@ -272,16 +288,19 @@ static bool bt_tags_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
> * We can hit rq == NULL here, because the tagging functions
> * test and set the bit before assigning ->rqs[].
> */
> + if (iter_static_rqs)
I think this local variable just obsfucates what is going on here.
Otherwise this looks good:
Reviewed-by: Christoph Hellwig <hch@lst.de>
next prev parent reply other threads:[~2021-05-06 6:55 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-05 14:58 [PATCH V5 0/4] blk-mq: fix request UAF related with iterating over tagset requests Ming Lei
2021-05-05 14:58 ` [PATCH V5 1/4] block: avoid double io accounting for flush request Ming Lei
2021-05-06 6:44 ` Christoph Hellwig
2021-05-05 14:58 ` [PATCH V5 2/4] blk-mq: grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter Ming Lei
2021-05-06 6:54 ` Christoph Hellwig [this message]
2021-05-06 7:30 ` Ming Lei
2021-05-05 14:58 ` [PATCH V5 3/4] blk-mq: clear stale request in tags->rq[] before freeing one request pool Ming Lei
2021-05-06 7:12 ` Christoph Hellwig
2021-05-06 7:34 ` Ming Lei
2021-05-06 12:18 ` Christoph Hellwig
2021-05-06 13:38 ` Ming Lei
2021-05-07 6:57 ` Christoph Hellwig
2021-05-07 7:30 ` Ming Lei
2021-05-06 14:51 ` Bart Van Assche
2021-05-07 0:11 ` Ming Lei
2021-05-07 1:10 ` Bart Van Assche
2021-05-07 2:05 ` Ming Lei
2021-05-07 3:16 ` Bart Van Assche
2021-05-07 6:31 ` Ming Lei
2021-05-07 6:52 ` Christoph Hellwig
2021-05-08 2:02 ` Bart Van Assche
2021-05-06 15:02 ` Bart Van Assche
2021-05-07 0:13 ` Ming Lei
2021-05-07 1:11 ` Bart Van Assche
2021-05-07 2:06 ` Ming Lei
2021-05-05 14:58 ` [PATCH V5 4/4] blk-mq: clearing flush request reference in tags->rqs[] Ming Lei
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