driver core: fix parent lock use-after-free on USB disconnect

USB interfaces should be probed with their parent USB device lock held
and the USB bus therefore sets the need_parent_lock bus flag so that
driver core takes the parent lock when needed.

Driver core is only guaranteed to hold a reference to the parent device
during initial probe however and nothing prevents the device and its
parent from being deregistered and the parent potentially freed, for
example, while iterating over devices in driver_attach() or
bus_rescan_devices_helper().

Since commit 524134d422 ("USB: don't cancel queued resets when
unbinding drivers") USB interfaces hold a reference to their parent USB
device, but a parent hub may still go away while probing a USB device
(e.g. via the drivers_probe sysfs interface). This can lead to a
use-after-free when taking the parent device lock before checking the
device->p->dead flag of the device being probed.

As only USB interfaces actually need the parent lock, make the
need_parent_lock feature even more fine grained by making it a device
type rather than bus feature. By requiring that any users also make sure
that their devices hold a reference to their parents (like USB does),
driver core can lock a device and its parent without first checking if
the device has been deregistered.

Note that this will also increase parallelism when using asynchronous
probe as USB devices connected to the same hub can now be probed in
parallel.

Fixes: bf74ad5bc4 ("[PATCH] Hold the device's parent's lock during probe and remove")
Cc: stable@vger.kernel.org	# 2.6.16: 524134d42231: USB: don't cancel queued resets when unbinding drivers
Cc: stable@vger.kernel.org	# 2.6.16
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://patch.msgid.link/20261014133109.1392265-2-johan@kernel.org
[ Fix mention of bus vs. device type in __device_driver_{un}lock().
  - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

drivers/base/bus.c

@@ -849,10 +849,10 @@ static int __must_check bus_rescan_devices_helper(struct device *dev,
 	int ret = 0;
 
 	if (!dev->driver) {
-		if (dev->parent && dev->bus->need_parent_lock)
+		if (dev->type && dev->type->need_parent_lock)
 			device_lock(dev->parent);
 		ret = device_attach(dev);
-		if (dev->parent && dev->bus->need_parent_lock)
+		if (dev->type && dev->type->need_parent_lock)
 			device_unlock(dev->parent);
 	}
 	return ret < 0 ? ret : 0;

drivers/base/dd.c

@@ -1158,7 +1158,7 @@ void device_initial_probe(struct device *dev)
 /*
  * __device_driver_lock - acquire locks needed to manipulate dev->drv
  * @dev: Device we will update driver info for
- * @parent: Parent device. Needed if the bus requires parent lock
+ * @parent: Parent device. Needed if the device type requires parent lock
  *
  * This function will take the required locks for manipulating dev->drv.
  * Normally this will just be the @dev lock, but when called for a USB
@@ -1166,7 +1166,7 @@ void device_initial_probe(struct device *dev)
  */
 static void __device_driver_lock(struct device *dev, struct device *parent)
 {
-	if (parent && dev->bus->need_parent_lock)
+	if (dev->type && dev->type->need_parent_lock && parent)
 		device_lock(parent);
 	device_lock(dev);
 }
@@ -1174,7 +1174,7 @@ static void __device_driver_lock(struct device *dev, struct device *parent)
 /*
  * __device_driver_unlock - release locks needed to manipulate dev->drv
  * @dev: Device we will update driver info for
- * @parent: Parent device. Needed if the bus requires parent lock
+ * @parent: Parent device. Needed if the device type requires parent lock
  *
  * This function will release the required locks for manipulating dev->drv.
  * Normally this will just be the @dev lock, but when called for a
@@ -1183,7 +1183,7 @@ static void __device_driver_lock(struct device *dev, struct device *parent)
 static void __device_driver_unlock(struct device *dev, struct device *parent)
 {
 	device_unlock(dev);
-	if (parent && dev->bus->need_parent_lock)
+	if (dev->type && dev->type->need_parent_lock && parent)
 		device_unlock(parent);
 }
 

drivers/usb/core/driver.c

@@ -2081,5 +2081,4 @@ const struct bus_type usb_bus_type = {
 	.name =		"usb",
 	.match =	usb_device_match,
 	.uevent =	usb_uevent,
-	.need_parent_lock =	true,
 };

drivers/usb/core/message.c

@@ -1916,6 +1916,7 @@ const struct device_type usb_if_device_type = {
 	.name =		"usb_interface",
 	.release =	usb_release_interface,
 	.uevent =	usb_if_uevent,
+	.need_parent_lock =	true,
 };
 
 static struct usb_interface_assoc_descriptor *find_iad(struct usb_device *dev,

include/linux/device.h

@@ -83,6 +83,10 @@ int subsys_virtual_register(const struct bus_type *subsys,
  * information, equivalent to the kobj_type of a kobject.
  * If "name" is specified, the uevent will contain it in
  * the DEVTYPE variable.
+ *
+ * @need_parent_lock:	When probing or removing a device of this type,
+ *			driver core should lock the device's parent. Note that
+ *			the device must hold a reference to its parent.
  */
 struct device_type {
 	const char *name;
@@ -93,6 +97,7 @@ struct device_type {
 	void (*release)(struct device *dev);
 
 	const struct dev_pm_ops *pm;
+	bool need_parent_lock;
 };
 
 /**

include/linux/device/bus.h

@@ -68,8 +68,6 @@ struct fwnode_handle;
  * @driver_override:	Set to true if this bus supports the driver_override
  *			mechanism, which allows userspace to force a specific
  *			driver to bind to a device via a sysfs attribute.
- * @need_parent_lock:	When probing or removing a device on this bus, the
- *			device core should lock the device's parent.
  *
  * A bus is a channel between the processor and one or more devices. For the
  * purposes of the device model, all devices are connected via a bus, even if
@@ -110,7 +108,6 @@ struct bus_type {
 	const struct dev_pm_ops *pm;
 
 	bool driver_override;
-	bool need_parent_lock;
 };
 
 int __must_check bus_register(const struct bus_type *bus);