linux-kernel - [PATCH 08/16] blk-mq: fix blk_mq_tags double free while nr

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20250814033522.770575-9-yukuai1@huaweicloud.com>
Date: Thu, 14 Aug 2025 11:35:14 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: axboe@...nel.dk,
	yukuai3@...wei.com,
	bvanassche@....org,
	nilay@...ux.ibm.com,
	hare@...e.de,
	ming.lei@...hat.com
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yukuai1@...weicloud.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com,
	johnny.chenyi@...wei.com
Subject: [PATCH 08/16] blk-mq: fix blk_mq_tags double free while nr_requests grown

From: Yu Kuai <yukuai3@...wei.com>

In the case user trigger tags grow by queue sysfs attribute nr_requests,
hctx->sched_tags will be freed directly and replaced with a new
allocated tags, see blk_mq_tag_update_depth().

The problem is that hctx->sched_tags is from elevator->et->tags, while
et->tags is still the freed tags, hence later elevator exist will try to
free the tags again, causing kernel panic.

Fix this problem by using new halper blk_mq_alloc_sched_tags() to
allocate a new sched_tags. Meanwhile, there is a longterm problem can be
fixed as well:

If blk_mq_tag_update_depth() succeed for previous hctx, then bitmap depth
is updated, however, if following hctx failed, q->nr_requests is not
updated and the previous hctx->sched_tags endup bigger than q->nr_requests.

Fixes: f5a6604f7a44 ("block: fix lockdep warning caused by lock dependency in elv_iosched_store")
Fixes: e3a2b3f931f5 ("blk-mq: allow changing of queue depth through sysfs")
Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/blk-mq.c | 31 ++++++++++++++++++++-----------
 1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index a7d6a20c1524..f1c11f591c27 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4917,6 +4917,23 @@ void blk_mq_free_tag_set(struct blk_mq_tag_set *set)
 }
 EXPORT_SYMBOL(blk_mq_free_tag_set);
 
+static int blk_mq_sched_grow_tags(struct request_queue *q, unsigned int nr)
+{
+	struct elevator_tags *et =
+		blk_mq_alloc_sched_tags(q->tag_set, q->nr_hw_queues, nr);
+	struct blk_mq_hw_ctx *hctx;
+	unsigned long i;
+
+	if (!et)
+		return -ENOMEM;
+
+	blk_mq_free_sched_tags(q->elevator->et, q->tag_set);
+	queue_for_each_hw_ctx(q, hctx, i)
+		hctx->sched_tags = et->tags[i];
+	q->elevator->et = et;
+	return 0;
+}
+
 int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
 {
 	struct blk_mq_tag_set *set = q->tag_set;
@@ -4940,17 +4957,9 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
 			sbitmap_queue_resize(&hctx->sched_tags->bitmap_tags,
 				nr - hctx->sched_tags->nr_reserved_tags);
 	} else {
-		queue_for_each_hw_ctx(q, hctx, i) {
-			/*
-			 * If we're using an MQ scheduler, just update the
-			 * scheduler queue depth. This is similar to what the
-			 * old code would do.
-			 */
-			ret = blk_mq_tag_update_depth(hctx,
-					&hctx->sched_tags, nr);
-			if (ret)
-				goto out;
-		}
+		ret = blk_mq_sched_grow_tags(q, nr);
+		if (ret)
+			goto out;
 	}
 
 	q->nr_requests = nr;
-- 
2.39.2