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ACPI: video: Fix use-after-free in acpi_video_switch_brightness()

PATCH Applied Yuhao Jiang 3 participants 3 messages Oct 22, 2025 – Oct 23, 2025

Subsystems (2)
Stable branch ACPI
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Yuhao Jiang

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#0 lore raw

PATCH v3 1/1 ACPI: video: Fix use-after-free in acpi_video_switch_brightness()

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 [email protected]
Signed-off-by Yuhao Jiang <[email protected]>

---
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/[email protected]/

---
 drivers/acpi/acpi_video.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
drivers/acpi/acpi_video.c +3 -1
index 103f29661576..be8e7e18abca 100644
@@ -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);
Signature · 1 line
2.34.1
Reviewed-by on v3 1/1
#1 lore raw

Hi,

Quoted 14 lines · 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.

Quoted 8 lines
Fixes 8ab58e8e7e097 ("ACPI / video: Fix backlight taking 2 steps on a brightness up/down keypress")
Cc [email protected]
Signed-off-by Yuhao Jiang <[email protected]>

---
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/[email protected]/

Thanks, patch looks good to me:

Reviewed-by Hans de Goede <[email protected]>

Regards,

Hans

Quoted 20 lines
---
 drivers/acpi/acpi_video.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
drivers/acpi/acpi_video.c +3 -1
index 103f29661576..be8e7e18abca 100644
@@ -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);
maintainer Applied
#2 lore raw
Quoted 27 lines · Hans de Goede

Hi,

Quoted 14 lines · 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.

Quoted 8 lines
Fixes 8ab58e8e7e097 ("ACPI / video: Fix backlight taking 2 steps on a brightness up/down keypress")
Cc [email protected]
Signed-off-by Yuhao Jiang <[email protected]>

---
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/[email protected]/

Quoted 3 lines

Thanks, patch looks good to me:

Reviewed-by Hans de Goede <[email protected]>

Applied as 6.18-rc material, thanks!

Quoted 21 lines
Quoted 20 lines
---
 drivers/acpi/acpi_video.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
drivers/acpi/acpi_video.c +3 -1
index 103f29661576..be8e7e18abca 100644
@@ -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);