[PATCH v3] ACPI: video: Fix use-after-free in acpi_video_switch_brightness()

[PATCH v3] ACPI: video: Fix use-after-free in acpi_video_switch_brightness()

[Yuhao Jiang]

The switch_brightness_work delayed work accesses device->brightness
and device->backlight, which are freed by
acpi_video_dev_unregister_backlight() during device removal.

If the work executes after acpi_video_bus_unregister_backlight()
frees these resources, it causes a use-after-free when
acpi_video_switch_brightness() dereferences device->brightness or
device->backlight.

Fix this by calling cancel_delayed_work_sync() for each device's
switch_brightness_work in acpi_video_bus_remove_notify_handler()
after removing the notify handler that queues the work. This ensures
the work completes before the memory is freed.

Fixes: 8ab58e8e7e097 ("ACPI / video: Fix backlight taking 2 steps on a brightness up/down keypress")
Cc: stable@vger.kernel.org
Signed-off-by: Yuhao Jiang <danisjiang@gmail.com>
---
Changes in v3:
- Move cancel_delayed_work_sync() to acpi_video_bus_remove_notify_handler()
  instead of acpi_video_bus_unregister_backlight() for better logic placement
- Link to v2: https://lore.kernel.org/all/20251022042514.2167599-1-danisjiang@gmail.com/
---
 drivers/acpi/acpi_video.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index 103f29661576..be8e7e18abca 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -1959,8 +1959,10 @@ static void acpi_video_bus_remove_notify_handler(struct acpi_video_bus *video)
 	struct acpi_video_device *dev;
 
 	mutex_lock(&video->device_list_lock);
-	list_for_each_entry(dev, &video->video_device_list, entry)
+	list_for_each_entry(dev, &video->video_device_list, entry) {
 		acpi_video_dev_remove_notify_handler(dev);
+		cancel_delayed_work_sync(&dev->switch_brightness_work);
+	}
 	mutex_unlock(&video->device_list_lock);
 
 	acpi_video_bus_stop_devices(video);
-- 
2.34.1

Re: [PATCH v3] ACPI: video: Fix use-after-free in acpi_video_switch_brightness()

[Hans de Goede]

Hi,

On 22-Oct-25 10:07 PM, Yuhao Jiang wrote:
> The switch_brightness_work delayed work accesses device->brightness
> and device->backlight, which are freed by
> acpi_video_dev_unregister_backlight() during device removal.
> 
> If the work executes after acpi_video_bus_unregister_backlight()
> frees these resources, it causes a use-after-free when
> acpi_video_switch_brightness() dereferences device->brightness or
> device->backlight.
> 
> Fix this by calling cancel_delayed_work_sync() for each device's
> switch_brightness_work in acpi_video_bus_remove_notify_handler()
> after removing the notify handler that queues the work. This ensures
> the work completes before the memory is freed.
> 
> Fixes: 8ab58e8e7e097 ("ACPI / video: Fix backlight taking 2 steps on a brightness up/down keypress")
> Cc: stable@vger.kernel.org
> Signed-off-by: Yuhao Jiang <danisjiang@gmail.com>
> ---
> Changes in v3:
> - Move cancel_delayed_work_sync() to acpi_video_bus_remove_notify_handler()
>   instead of acpi_video_bus_unregister_backlight() for better logic placement
> - Link to v2: https://lore.kernel.org/all/20251022042514.2167599-1-danisjiang@gmail.com/

Thanks, patch looks good to me:

Reviewed-by: Hans de Goede <hansg@kernel.org>

Regards,

Hans



> ---
>  drivers/acpi/acpi_video.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
> index 103f29661576..be8e7e18abca 100644
> --- a/drivers/acpi/acpi_video.c
> +++ b/drivers/acpi/acpi_video.c
> @@ -1959,8 +1959,10 @@ static void acpi_video_bus_remove_notify_handler(struct acpi_video_bus *video)
>  	struct acpi_video_device *dev;
>  
>  	mutex_lock(&video->device_list_lock);
> -	list_for_each_entry(dev, &video->video_device_list, entry)
> +	list_for_each_entry(dev, &video->video_device_list, entry) {
>  		acpi_video_dev_remove_notify_handler(dev);
> +		cancel_delayed_work_sync(&dev->switch_brightness_work);
> +	}
>  	mutex_unlock(&video->device_list_lock);
>  
>  	acpi_video_bus_stop_devices(video);

Re: [PATCH v3] ACPI: video: Fix use-after-free in acpi_video_switch_brightness()

[Rafael J. Wysocki]

On Thu, Oct 23, 2025 at 3:25 PM Hans de Goede <hansg@kernel.org> wrote:
>
> Hi,
>
> On 22-Oct-25 10:07 PM, Yuhao Jiang wrote:
> > The switch_brightness_work delayed work accesses device->brightness
> > and device->backlight, which are freed by
> > acpi_video_dev_unregister_backlight() during device removal.
> >
> > If the work executes after acpi_video_bus_unregister_backlight()
> > frees these resources, it causes a use-after-free when
> > acpi_video_switch_brightness() dereferences device->brightness or
> > device->backlight.
> >
> > Fix this by calling cancel_delayed_work_sync() for each device's
> > switch_brightness_work in acpi_video_bus_remove_notify_handler()
> > after removing the notify handler that queues the work. This ensures
> > the work completes before the memory is freed.
> >
> > Fixes: 8ab58e8e7e097 ("ACPI / video: Fix backlight taking 2 steps on a brightness up/down keypress")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Yuhao Jiang <danisjiang@gmail.com>
> > ---
> > Changes in v3:
> > - Move cancel_delayed_work_sync() to acpi_video_bus_remove_notify_handler()
> >   instead of acpi_video_bus_unregister_backlight() for better logic placement
> > - Link to v2: https://lore.kernel.org/all/20251022042514.2167599-1-danisjiang@gmail.com/
>
> Thanks, patch looks good to me:
>
> Reviewed-by: Hans de Goede <hansg@kernel.org>

Applied as 6.18-rc material, thanks!

> > ---
> >  drivers/acpi/acpi_video.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
> > index 103f29661576..be8e7e18abca 100644
> > --- a/drivers/acpi/acpi_video.c
> > +++ b/drivers/acpi/acpi_video.c
> > @@ -1959,8 +1959,10 @@ static void acpi_video_bus_remove_notify_handler(struct acpi_video_bus *video)
> >       struct acpi_video_device *dev;
> >
> >       mutex_lock(&video->device_list_lock);
> > -     list_for_each_entry(dev, &video->video_device_list, entry)
> > +     list_for_each_entry(dev, &video->video_device_list, entry) {
> >               acpi_video_dev_remove_notify_handler(dev);
> > +             cancel_delayed_work_sync(&dev->switch_brightness_work);
> > +     }
> >       mutex_unlock(&video->device_list_lock);
> >
> >       acpi_video_bus_stop_devices(video);
>