linux-kernel - [PATCH AUTOSEL 4.19 6/7] blk-mq: protect q->elevator by ->sysfs_lock in blk_mq_elv_switch

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Date:   Tue, 21 Jun 2022 16:51:28 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Ming Lei <ming.lei@...hat.com>, Christoph Hellwig <hch@....de>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>,
        linux-block@...r.kernel.org
Subject: [PATCH AUTOSEL 4.19 6/7] blk-mq: protect q->elevator by ->sysfs_lock in blk_mq_elv_switch_none

From: Ming Lei <ming.lei@...hat.com>

[ Upstream commit 5fd7a84a09e640016fe106dd3e992f5210e23dc7 ]

elevator can be tore down by sysfs switch interface or disk release, so
hold ->sysfs_lock before referring to q->elevator, then potential
use-after-free can be avoided.

Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Ming Lei <ming.lei@...hat.com>
Link: https://lore.kernel.org/r/20220616014401.817001-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 block/blk-mq.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index ae70b4809bec..3a791597c534 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2940,12 +2940,14 @@ static bool blk_mq_elv_switch_none(struct list_head *head,
 	if (!qe)
 		return false;
 
+	/* q->elevator needs protection from ->sysfs_lock */
+	mutex_lock(&q->sysfs_lock);
+
 	INIT_LIST_HEAD(&qe->node);
 	qe->q = q;
 	qe->type = q->elevator->type;
 	list_add(&qe->node, head);
 
-	mutex_lock(&q->sysfs_lock);
 	/*
 	 * After elevator_switch_mq, the previous elevator_queue will be
 	 * released by elevator_release. The reference of the io scheduler
-- 
2.35.1