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@zju.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);
-- 
2.17.1

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@zju.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@physik.fu-berlin.de>

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913

On Wed, Aug 2, 2023 at 5:46 AM Duoming Zhou <duoming@zju.edu.cn> 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@zju.edu.cn>

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds