device: add device_change_owner()

Add a helper to change the owner of a device's sysfs entries. This
needs to happen when the ownership of a device is changed, e.g. when
moving network devices between network namespaces.
This function will be used to correctly account for ownership changes,
e.g. when moving network devices between network namespaces.

Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/base/core.c

···
 }
 EXPORT_SYMBOL_GPL(device_move);
 
+static int device_attrs_change_owner(struct device *dev, kuid_t kuid,
+				     kgid_t kgid)
+{
+	struct kobject *kobj = &dev->kobj;
+	struct class *class = dev->class;
+	const struct device_type *type = dev->type;
+	int error;
+
+	if (class) {
+		/*
+		 * Change the device groups of the device class for @dev to
+		 * @kuid/@kgid.
+		 */
+		error = sysfs_groups_change_owner(kobj, class->dev_groups, kuid,
+						  kgid);
+		if (error)
+			return error;
+	}
+
+	if (type) {
+		/*
+		 * Change the device groups of the device type for @dev to
+		 * @kuid/@kgid.
+		 */
+		error = sysfs_groups_change_owner(kobj, type->groups, kuid,
+						  kgid);
+		if (error)
+			return error;
+	}
+
+	/* Change the device groups of @dev to @kuid/@kgid. */
+	error = sysfs_groups_change_owner(kobj, dev->groups, kuid, kgid);
+	if (error)
+		return error;
+
+	if (device_supports_offline(dev) && !dev->offline_disabled) {
+		/* Change online device attributes of @dev to @kuid/@kgid. */
+		error = sysfs_file_change_owner(kobj, dev_attr_online.attr.name,
+						kuid, kgid);
+		if (error)
+			return error;
+	}
+
+	return 0;
+}
+
+/**
+ * device_change_owner - change the owner of an existing device.
+ * @dev: device.
+ * @kuid: new owner's kuid
+ * @kgid: new owner's kgid
+ *
+ * This changes the owner of @dev and its corresponding sysfs entries to
+ * @kuid/@kgid. This function closely mirrors how @dev was added via driver
+ * core.
+ *
+ * Returns 0 on success or error code on failure.
+ */
+int device_change_owner(struct device *dev, kuid_t kuid, kgid_t kgid)
+{
+	int error;
+	struct kobject *kobj = &dev->kobj;
+
+	dev = get_device(dev);
+	if (!dev)
+		return -EINVAL;
+
+	/*
+	 * Change the kobject and the default attributes and groups of the
+	 * ktype associated with it to @kuid/@kgid.
+	 */
+	error = sysfs_change_owner(kobj, kuid, kgid);
+	if (error)
+		goto out;
+
+	/*
+	 * Change the uevent file for @dev to the new owner. The uevent file
+	 * was created in a separate step when @dev got added and we mirror
+	 * that step here.
+	 */
+	error = sysfs_file_change_owner(kobj, dev_attr_uevent.attr.name, kuid,
+					kgid);
+	if (error)
+		goto out;
+
+	/*
+	 * Change the device groups, the device groups associated with the
+	 * device class, and the groups associated with the device type of @dev
+	 * to @kuid/@kgid.
+	 */
+	error = device_attrs_change_owner(dev, kuid, kgid);
+	if (error)
+		goto out;
+
+#ifdef CONFIG_BLOCK
+	if (sysfs_deprecated && dev->class == &block_class)
+		goto out;
+#endif
+
+	/*
+	 * Change the owner of the symlink located in the class directory of
+	 * the device class associated with @dev which points to the actual
+	 * directory entry for @dev to @kuid/@kgid. This ensures that the
+	 * symlink shows the same permissions as its target.
+	 */
+	error = sysfs_link_change_owner(&dev->class->p->subsys.kobj, &dev->kobj,
+					dev_name(dev), kuid, kgid);
+	if (error)
+		goto out;
+
+out:
+	put_device(dev);
+	return error;
+}
+EXPORT_SYMBOL_GPL(device_change_owner);
+
 /**
  * device_shutdown - call ->shutdown() on each device to shutdown.
  */

include/linux/device.h

···
 extern int device_rename(struct device *dev, const char *new_name);
 extern int device_move(struct device *dev, struct device *new_parent,
 		       enum dpm_order dpm_order);
+extern int device_change_owner(struct device *dev, kuid_t kuid, kgid_t kgid);
 extern const char *device_get_devnode(struct device *dev,
 				      umode_t *mode, kuid_t *uid, kgid_t *gid,
 				      const char **tmp);