Re: [PATCH] block: fix use-after-free of q->q_usage_counter

[Ming Lei <ming.lei@redhat.com>]

On Thu, Sep 21, 2023 at 11:20:12AM -0700, Saranya Muruganandam wrote:
> From: Ming Lei <ming.lei@redhat.com>
> 
> commit d36a9ea5e7766961e753ee38d4c331bbe6ef659b upstream.
> 
> 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.
> 
> Backport-notes: Not a clean cherry-pick since a lot has changed,
> however essentially the same fix.
> 
> Reported-by: Zhang Wensheng <zhangwensheng@huaweicloud.com>
> Reported-by: Zhong Jinghua <zhongjinghua@huawei.com>
> Link: https://lore.kernel.org/linux-block/Y5prfOjyyjQKUrtH@T590/T/#u
> Link: https://lore.kernel.org/lkml/Y4%2FmzMd4evRg9yDi@fedora/
> Cc: Hillf Danton <hdanton@sina.com>
> Cc: Yu Kuai <yukuai3@huawei.com>
> Cc: Dennis Zhou <dennis@kernel.org>
> Fixes: 2b0d3d3e4fcf ("percpu_ref: reduce memory footprint of percpu_ref in fast path")
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> Link: https://lore.kernel.org/r/20221215021629.74870-1-ming.lei@redhat.com
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> Signed-off-by: Saranya Muruganandam <saranyamohan@google.com>
> ---
>  block/blk-core.c  | 2 --
>  block/blk-sysfs.c | 2 ++
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index d0d0dd8151f7..e5eeec801f56 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -414,8 +414,6 @@ void blk_cleanup_queue(struct request_queue *q)
>  		blk_mq_sched_free_requests(q);
>  	mutex_unlock(&q->sysfs_lock);
>  
> -	percpu_ref_exit(&q->q_usage_counter);
> -
>  	/* @q is and will stay empty, shutdown and put */
>  	blk_put_queue(q);
>  }
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index 8c5816364dd1..9174137a913c 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -726,6 +726,8 @@ static void blk_free_queue_rcu(struct rcu_head *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);
>  }

Looks fine.

BTW, you should have provided target stable tree release info, otherwise how
you expect people to review?

Thanks,
Ming