ACPI: video: Fix NULL pointer dereference in acpi_video_bus_add()

acpi_video_bus_add_notify_handler() could free video->input and
set it to NULL on failure, but this failure would be missed in its
caller acpi_video_bus_add(). As a result, when an error happens in
acpi_dev_install_notify_handler(), acpi_video_bus_add() would call
acpi_video_bus_remove_notify_handler(), where a potential NULL pointer
video->input is dereferenced in input_unregister_device().

Fix this by adding a return value check and adjusting the following
error handling code.

Fixes: 6f701681 ("ACPI: video: Install Notify() handler directly")
Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpi_video.c

@@ -2057,7 +2057,9 @@ static int acpi_video_bus_add(struct acpi_device *device)
 	    !auto_detect)
 		acpi_video_bus_register_backlight(video);
 
-	acpi_video_bus_add_notify_handler(video);
+	error = acpi_video_bus_add_notify_handler(video);
+	if (error)
+		goto err_del;
 
 	error = acpi_dev_install_notify_handler(device, ACPI_DEVICE_NOTIFY,
 						acpi_video_bus_notify);
@@ -2067,10 +2069,11 @@ static int acpi_video_bus_add(struct acpi_device *device)
 	return 0;
 
 err_remove:
+	acpi_video_bus_remove_notify_handler(video);
+err_del:
 	mutex_lock(&video_list_lock);
 	list_del(&video->entry);
 	mutex_unlock(&video_list_lock);
-	acpi_video_bus_remove_notify_handler(video);
 	acpi_video_bus_unregister_backlight(video);
 err_put_video:
 	acpi_video_bus_put_devices(video);