gpio: virtuser: fix UAF in configfs release path

The gpio-virtuser configfs release path uses guard(mutex) to protect
the device structure. However, the device is freed before the guard
cleanup runs, causing mutex_unlock() to operate on freed memory.

Specifically, gpio_virtuser_device_config_group_release() destroys
the mutex and frees the device while still inside the guard(mutex)
scope. When the function returns, the guard cleanup invokes
mutex_unlock(&dev->lock), resulting in a slab use-after-free.

Limit the mutex lifetime by using a scoped_guard() only around the
activation check, so that the lock is released before mutex_destroy()
and kfree() are called.

Fixes: 91581c4 ("gpio: virtuser: new virtual testing driver for the GPIO API")
Signed-off-by: Yuhao Huang <nekowong743@gmail.com>
Link: https://lore.kernel.org/r/20260126040348.11167-1-yuhaohuang@YuhaodeMacBook-Pro.local
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>

Author: CeS-3

drivers/gpio/gpio-virtuser.c

@@ -1682,10 +1682,10 @@ static void gpio_virtuser_device_config_group_release(struct config_item *item)
 {
 	struct gpio_virtuser_device *dev = to_gpio_virtuser_device(item);
 
-	guard(mutex)(&dev->lock);
-
-	if (gpio_virtuser_device_is_live(dev))
-		gpio_virtuser_device_deactivate(dev);
+	scoped_guard(mutex, &dev->lock) {
+		if (gpio_virtuser_device_is_live(dev))
+			gpio_virtuser_device_deactivate(dev);
+	}
 
 	mutex_destroy(&dev->lock);
 	ida_free(&gpio_virtuser_ida, dev->id);