linux-kernel - Re: [PATCH] sh: push-switch: reorder cleanup operations to avoid UAF bug

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Date:   Fri, 08 Sep 2023 11:33:04 +0200
From:   John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To:     Duoming Zhou <duoming@....edu.cn>, ysato@...rs.sourceforge.jp
Cc:     dalias@...c.org, kvalo@...nel.org, pavel@....cz, pabeni@...hat.com,
        rostedt@...dmis.org, linux-sh@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sh: push-switch: reorder cleanup operations to avoid
 UAF bug

On Wed, 2023-08-02 at 11:37 +0800, Duoming Zhou wrote:
> The original code puts flush_work() before timer_shutdown_sync()
> in switch_drv_remove(). Although we use flush_work() to stop
> the worker, it could be re-scheduled in switch_timer. As a result,
> the UAF bug will happen. The detail is shown below:
> 
>       (cpu 0)                    |      (cpu 1)
> switch_drv_remove()              |
>  flush_work()                    |
>   ...                            |  switch_timer //timer
>                                  |   schedule_work(&psw->work)
>  timer_shutdown_sync()           |
>  ...                             |  switch_work_handler //worker
>  kfree(psw) //free               |
>                                  |   psw->state = 0 //use
> 
> This patch puts timer_shutdown_sync() before flush_work() to
> mitigate the bugs. As a result, the worker and timer could
> be stopped safely before the deallocate operations.
> 
> Fixes: 9f5e8eee5cfe ("sh: generic push-switch framework.")
> Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> ---
>  arch/sh/drivers/push-switch.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/sh/drivers/push-switch.c b/arch/sh/drivers/push-switch.c
> index c95f48ff3f6..6ecba5f521e 100644
> --- a/arch/sh/drivers/push-switch.c
> +++ b/arch/sh/drivers/push-switch.c
> @@ -101,8 +101,8 @@ static int switch_drv_remove(struct platform_device *pdev)
>  		device_remove_file(&pdev->dev, &dev_attr_switch);
>  
>  	platform_set_drvdata(pdev, NULL);
> -	flush_work(&psw->work);
>  	timer_shutdown_sync(&psw->debounce);
> +	flush_work(&psw->work);
>  	free_irq(irq, pdev);
>  
>  	kfree(psw);

Reviewed-by: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>

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