vdpa: use generic driver_override infrastructure

When a driver is probed through __driver_attach(), the bus' match()
callback is called without the device lock held, thus accessing the
driver_override field without a lock, which can cause a UAF.

Fix this by using the driver-core driver_override infrastructure taking
care of proper locking internally.

Note that calling match() from __driver_attach() without the device lock
held is intentional. [1]

Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/ [1]
Reported-by: Gui-Dong Han <hanguidong02@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220789
Fixes: 539fec7 ("vdpa: add driver_override support")
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://patch.msgid.link/20260324005919.2408620-9-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Author: Danilo Krummrich

drivers/vdpa/vdpa.c

@@ -67,57 +67,20 @@ static void vdpa_dev_remove(struct device *d)
 
 static int vdpa_dev_match(struct device *dev, const struct device_driver *drv)
 {
-	struct vdpa_device *vdev = dev_to_vdpa(dev);
+	int ret;
 
 	/* Check override first, and if set, only use the named driver */
-	if (vdev->driver_override)
-		return strcmp(vdev->driver_override, drv->name) == 0;
+	ret = device_match_driver_override(dev, drv);
+	if (ret >= 0)
+		return ret;
 
 	/* Currently devices must be supported by all vDPA bus drivers */
 	return 1;
 }
 
-static ssize_t driver_override_store(struct device *dev,
-				     struct device_attribute *attr,
-				     const char *buf, size_t count)
-{
-	struct vdpa_device *vdev = dev_to_vdpa(dev);
-	int ret;
-
-	ret = driver_set_override(dev, &vdev->driver_override, buf, count);
-	if (ret)
-		return ret;
-
-	return count;
-}
-
-static ssize_t driver_override_show(struct device *dev,
-				    struct device_attribute *attr, char *buf)
-{
-	struct vdpa_device *vdev = dev_to_vdpa(dev);
-	ssize_t len;
-
-	device_lock(dev);
-	len = sysfs_emit(buf, "%s\n", vdev->driver_override);
-	device_unlock(dev);
-
-	return len;
-}
-static DEVICE_ATTR_RW(driver_override);
-
-static struct attribute *vdpa_dev_attrs[] = {
-	&dev_attr_driver_override.attr,
-	NULL,
-};
-
-static const struct attribute_group vdpa_dev_group = {
-	.attrs  = vdpa_dev_attrs,
-};
-__ATTRIBUTE_GROUPS(vdpa_dev);
-
 static const struct bus_type vdpa_bus = {
 	.name  = "vdpa",
-	.dev_groups = vdpa_dev_groups,
+	.driver_override = true,
 	.match = vdpa_dev_match,
 	.probe = vdpa_dev_probe,
 	.remove = vdpa_dev_remove,
@@ -132,7 +95,6 @@ static void vdpa_release_dev(struct device *d)
 		ops->free(vdev);
 
 	ida_free(&vdpa_index_ida, vdev->index);
-	kfree(vdev->driver_override);
 	kfree(vdev);
 }
 

include/linux/vdpa.h

@@ -72,9 +72,6 @@ struct vdpa_mgmt_dev;
  * struct vdpa_device - representation of a vDPA device
  * @dev: underlying device
  * @vmap: the metadata passed to upper layer to be used for mapping
- * @driver_override: driver name to force a match; do not set directly,
- *                   because core frees it; use driver_set_override() to
- *                   set or clear it.
  * @config: the configuration ops for this device.
  * @map: the map ops for this device
  * @cf_lock: Protects get and set access to configuration layout.
@@ -90,7 +87,6 @@ struct vdpa_mgmt_dev;
 struct vdpa_device {
 	struct device dev;
 	union virtio_map vmap;
-	const char *driver_override;
 	const struct vdpa_config_ops *config;
 	const struct virtio_map_ops *map;
 	struct rw_semaphore cf_lock; /* Protects get/set config */