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From: Ming Lei <ming.lei@redhat.com>
To: John Garry <john.garry@huawei.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, Bart Van Assche <bvanassche@acm.org>,
	Khazhy Kumykov <khazhy@google.com>,
	Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>,
	Hannes Reinecke <hare@suse.de>,
	David Jeffery <djeffery@redhat.com>
Subject: Re: [PATCH V4 0/4] blk-mq: fix request UAF related with iterating over tagset requests
Date: Tue, 4 May 2021 19:43:51 +0800	[thread overview]
Message-ID: <YJEzd8IYtw4GXrlT@T590> (raw)
In-Reply-To: <fb0804e5-bfae-62ac-c3e6-d46a9a33ca53@huawei.com>

On Tue, May 04, 2021 at 11:15:37AM +0100, John Garry wrote:
> On 29/04/2021 03:34, Ming Lei wrote:
> > Hi Jens,
> > 
> > This patchset fixes the request UAF issue by one simple approach,
> > without clearing ->rqs[] in fast path.
> > 
> > 1) grab request's ref before calling ->fn in blk_mq_tagset_busy_iter,
> > and release it after calling ->fn, so ->fn won't be called for one
> > request if its queue is frozen, done in 2st patch
> > 
> > 2) clearing any stale request referred in ->rqs[] before freeing the
> > request pool, one per-tags spinlock is added for protecting
> > grabbing request ref vs. clearing ->rqs[tag], so UAF by refcount_inc_not_zero
> > in bt_tags_iter() is avoided, done in 3rd patch.
> > 
> 
> I had a go at testing this. Without any modifications for testing, it looks
> ok.
> 
> However I also tested by adding an artificial delay in bt_iter() - otherwise
> it may not be realistic to trigger some UAF issues in sane timeframes.
> 
> So I made this change:
> 
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -215,8 +215,11 @@ static bool bt_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 (rq && rq->q == hctx->queue && rq->mq_hctx == hctx)
> -               return iter_data->fn(hctx, rq, iter_data->data, reserved);
> +       if (rq) {
> +               mdelay(50);
> +               if (rq->q == hctx->queue && rq->mq_hctx == hctx)
> +   		  return iter_data->fn(hctx, rq, iter_data->data, reserved);
> +       }
>         return true;
>  }

hammmm, forget to cover bt_iter(), please test the following delta
patch:


diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index a3be267212b9..27815114ee3f 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -206,18 +206,28 @@ static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
 	struct blk_mq_tags *tags = hctx->tags;
 	bool reserved = iter_data->reserved;
 	struct request *rq;
+	unsigned long flags;
+	bool ret = true;
 
 	if (!reserved)
 		bitnr += tags->nr_reserved_tags;
-	rq = tags->rqs[bitnr];
 
+	spin_lock_irqsave(&tags->lock, flags);
+	rq = tags->rqs[bitnr];
 	/*
 	 * We can hit rq == NULL here, because the tagging functions
 	 * test and set the bit before assigning ->rqs[].
 	 */
-	if (rq && rq->q == hctx->queue && rq->mq_hctx == hctx)
-		return iter_data->fn(hctx, rq, iter_data->data, reserved);
-	return true;
+	if (!rq || !refcount_inc_not_zero(&rq->ref)) {
+		spin_unlock_irqrestore(&tags->lock, flags);
+		return true;
+	}
+	spin_unlock_irqrestore(&tags->lock, flags);
+
+	if (rq->q == hctx->queue && rq->mq_hctx == hctx)
+		ret = iter_data->fn(hctx, rq, iter_data->data, reserved);
+	blk_mq_put_rq_ref(rq);
+	return ret;
 }
 
 /**

Thanks, 
Ming


  reply	other threads:[~2021-05-04 11:44 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-29  2:34 [PATCH V4 0/4] blk-mq: fix request UAF related with iterating over tagset requests Ming Lei
2021-04-29  2:34 ` [PATCH V4 1/4] block: avoid double io accounting for flush request Ming Lei
2021-04-30  2:51   ` Bart Van Assche
2021-04-30  3:12     ` Ming Lei
2021-04-29  2:34 ` [PATCH V4 2/4] blk-mq: grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter Ming Lei
2021-04-30  3:06   ` Bart Van Assche
2021-04-29  2:34 ` [PATCH V4 3/4] blk-mq: clear stale request in tags->rq[] before freeing one request pool Ming Lei
2021-04-29 14:02   ` David Jeffery
2021-04-29  2:34 ` [PATCH V4 4/4] blk-mq: clearing flush request reference in tags->rqs[] Ming Lei
2021-04-29 14:13   ` David Jeffery
2021-04-30  3:05   ` Bart Van Assche
2021-05-04  7:29 ` [PATCH V4 0/4] blk-mq: fix request UAF related with iterating over tagset requests Ming Lei
2021-05-04 10:15 ` John Garry
2021-05-04 11:43   ` Ming Lei [this message]
2021-05-05 11:19     ` John Garry
2021-05-05 14:28       ` Ming Lei

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