[PATCH AUTOSEL 5.17 16/20] blk-mq: protect q->elevator by ->sysfs_lock in blk_mq_elv_switch_none

Sasha Levin
2022-06-21T21:00:48Z

From: Ming Lei <ming.lei@redhat.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@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20220616014401.817001-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.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 f18e1c9c3f4a..5021e8ed2053 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4433,12 +4433,14 @@ 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