linux-kernel - Re: [PATCH v2 2/6] blk-mq: Fix use after of free q->mq

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Date:	Wed, 8 Jul 2015 19:53:57 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Akinobu Mita <akinobu.mita@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v2 2/6] blk-mq: Fix use after of free q->mq_map

On Thu, Jul 2, 2015 at 10:29 PM, Akinobu Mita <akinobu.mita@...il.com> wrote:
> CPU hotplug handling for blk-mq (blk_mq_queue_reinit) updates
> q->mq_map by blk_mq_update_queue_map() for all request queues in
> all_q_list.  On the other hand, q->mq_map is released before deleting
> the queue from all_q_list.
>
> So if CPU hotplug event occurs in the window, invalid memory access
> can happen.  Fix it by releasing q->mq_map in blk_mq_release() to make
> it happen latter than removal from all_q_list.
>
> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> Suggested-by: Ming Lei <tom.leiming@...il.com>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Ming Lei <tom.leiming@...il.com>

Reviewed-by: Ming Lei <tom.leiming@...il.com>

> ---
>  block/blk-mq.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index f537796..c5da908 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1928,6 +1928,9 @@ void blk_mq_release(struct request_queue *q)
>                 kfree(hctx);
>         }
>
> +       kfree(q->mq_map);
> +       q->mq_map = NULL;
> +
>         kfree(q->queue_hw_ctx);
>
>         /* ctx kobj stays in queue_ctx */
> @@ -2073,11 +2076,6 @@ void blk_mq_free_queue(struct request_queue *q)
>         blk_mq_free_hw_queues(q, set);
>
>         percpu_ref_exit(&q->mq_usage_counter);
> -
> -       kfree(q->mq_map);
> -
> -       q->mq_map = NULL;
> -
>         mutex_lock(&all_q_mutex);
>         list_del_init(&q->all_q_node);
>         mutex_unlock(&all_q_mutex);
> --
> 1.9.1
>



-- 
Ming Lei
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