Re: [PATCH v3] drm/panthor: Fix UAF race between device unplug and FW event processing

[Boris Brezillon <boris.brezillon@collabora.com>]

On Mon, 27 Oct 2025 15:02:15 +0100
Ketil Johnsen <ketil.johnsen@arm.com> wrote:

> The function panthor_fw_unplug() will free the FW memory sections.
> The problem is that there could still be pending FW events which are yet
> not handled at this point. process_fw_events_work() can in this case try
> to access said freed memory.
> 
> Simply call disable_work_sync() to both drain and prevent future
> invocation of process_fw_events_work().
> 
> Signed-off-by: Ketil Johnsen <ketil.johnsen@arm.com>
> Fixes: de85488138247 ("drm/panthor: Add the scheduler logical block")

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

Would you mind sending a patch on top of this one turning all
cancel_[delayed_]work_sync() happening in the unplug path int
disable_[delayed_]work_sync(), so we're sure we won't face other "work
in queued after being cancelled" issues in the future.

> ---
> v2:
> - Followed Boris's advice and handle the race purely within the
>   scheduler block (by adding a destroyed state)
> 
> v3:
> - New approach, one single call to disable_work_sync()
> ---
>  drivers/gpu/drm/panthor/panthor_sched.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> index 0cc9055f4ee52..b7595beaa0205 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -3880,6 +3880,7 @@ void panthor_sched_unplug(struct panthor_device *ptdev)
>  	struct panthor_scheduler *sched = ptdev->scheduler;
>  
>  	cancel_delayed_work_sync(&sched->tick_work);
> +	disable_work_sync(&sched->fw_events_work);
>  
>  	mutex_lock(&sched->lock);
>  	if (sched->pm.has_ref) {