Patch "block: fix use-after-free of q->q_usage_counter" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    block: fix use-after-free of q->q_usage_counter

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     block-fix-use-after-free-of-q-q_usage_counter.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit b4737e2cd07ac2f7684bacb3cdeba0408b596ebb
Author: Ming Lei <ming.lei@xxxxxxxxxx>
Date:   Thu Dec 15 10:16:29 2022 +0800

    block: fix use-after-free of q->q_usage_counter
    
    [ Upstream commit d36a9ea5e7766961e753ee38d4c331bbe6ef659b ]
    
    For blk-mq, queue release handler is usually called after
    blk_mq_freeze_queue_wait() returns. However, the
    q_usage_counter->release() handler may not be run yet at that time, so
    this can cause a use-after-free.
    
    Fix the issue by moving percpu_ref_exit() into blk_free_queue_rcu().
    Since ->release() is called with rcu read lock held, it is agreed that
    the race should be covered in caller per discussion from the two links.
    
    Reported-by: Zhang Wensheng <zhangwensheng@xxxxxxxxxxxxxxx>
    Reported-by: Zhong Jinghua <zhongjinghua@xxxxxxxxxx>
    Link: https://lore.kernel.org/linux-block/Y5prfOjyyjQKUrtH@T590/T/#u
    Link: https://lore.kernel.org/lkml/Y4%2FmzMd4evRg9yDi@fedora/
    Cc: Hillf Danton <hdanton@xxxxxxxx>
    Cc: Yu Kuai <yukuai3@xxxxxxxxxx>
    Cc: Dennis Zhou <dennis@xxxxxxxxxx>
    Fixes: 2b0d3d3e4fcf ("percpu_ref: reduce memory footprint of percpu_ref in fast path")
    Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20221215021629.74870-1-ming.lei@xxxxxxxxxx
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/block/blk-core.c b/block/blk-core.c
index 815ffce6b988..52e77471a7ae 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -254,14 +254,15 @@ EXPORT_SYMBOL_GPL(blk_clear_pm_only);
 
 static void blk_free_queue_rcu(struct rcu_head *rcu_head)
 {
-	kmem_cache_free(blk_requestq_cachep,
-			container_of(rcu_head, struct request_queue, rcu_head));
+	struct request_queue *q = container_of(rcu_head,
+			struct request_queue, rcu_head);
+
+	percpu_ref_exit(&q->q_usage_counter);
+	kmem_cache_free(blk_requestq_cachep, q);
 }
 
 static void blk_free_queue(struct request_queue *q)
 {
-	percpu_ref_exit(&q->q_usage_counter);
-
 	if (q->poll_stat)
 		blk_stat_remove_callback(q, q->poll_cb);
 	blk_stat_free_callback(q->poll_cb);