USB: core: Change usb_get_device_descriptor() API

The usb_get_device_descriptor() routine reads the device descriptor
from the udev device and stores it directly in udev->descriptor. This
interface is error prone, because the USB subsystem expects in-memory
copies of a device's descriptors to be immutable once the device has
been initialized.

The interface is changed so that the device descriptor is left in a
kmalloc-ed buffer, not copied into the usb_device structure. A
pointer to the buffer is returned to the caller, who is then
responsible for kfree-ing it. The corresponding changes needed in the
various callers are fairly small.

Signed-off-by: Alan Stern <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/core/hcd.c

···
 {
 	struct device *parent_dev = hcd->self.controller;
 	struct usb_device *usb_dev = hcd->self.root_hub;
+	struct usb_device_descriptor *descr;
 	const int devnum = 1;
 	int retval;
 
···
 	mutex_lock(&usb_bus_idr_lock);
 
 	usb_dev->ep0.desc.wMaxPacketSize = cpu_to_le16(64);
-	retval = usb_get_device_descriptor(usb_dev, USB_DT_DEVICE_SIZE);
-	if (retval != sizeof usb_dev->descriptor) {
+	descr = usb_get_device_descriptor(usb_dev);
+	if (IS_ERR(descr)) {
+		retval = PTR_ERR(descr);
 		mutex_unlock(&usb_bus_idr_lock);
 		dev_dbg (parent_dev, "can't read %s device descriptor %d\n",
 				dev_name(&usb_dev->dev), retval);
-		return (retval < 0) ? retval : -EMSGSIZE;
+		return retval;
 	}
+	usb_dev->descriptor = *descr;
+	kfree(descr);
 
 	if (le16_to_cpu(usb_dev->descriptor.bcdUSB) >= 0x0201) {
 		retval = usb_get_bos_descriptor(usb_dev);

drivers/usb/core/hub.c

···
 	}
 
 	if (usb_dev->wusb) {
-		result = usb_get_device_descriptor(usb_dev, sizeof(usb_dev->descriptor));
-		if (result < 0) {
+		struct usb_device_descriptor *descr;
+
+		descr = usb_get_device_descriptor(usb_dev);
+		if (IS_ERR(descr)) {
+			result = PTR_ERR(descr);
 			dev_err(&usb_dev->dev, "can't re-read device descriptor for "
 				"authorization: %d\n", result);
 			goto error_device_descriptor;
 		}
+		usb_dev->descriptor = *descr;
+		kfree(descr);
 	}
 
 	usb_dev->authorized = 1;
···
 	const char		*driver_name;
 	bool			do_new_scheme;
 	int			maxp0;
-	struct usb_device_descriptor	*buf;
+	struct usb_device_descriptor	*buf, *descr;
 
 	buf = kmalloc(GET_DESCRIPTOR_BUFSIZE, GFP_NOIO);
 	if (!buf)
···
 		usb_ep0_reinit(udev);
 	}
 
-	retval = usb_get_device_descriptor(udev, USB_DT_DEVICE_SIZE);
-	if (retval < (signed)sizeof(udev->descriptor)) {
+	descr = usb_get_device_descriptor(udev);
+	if (IS_ERR(descr)) {
+		retval = PTR_ERR(descr);
 		if (retval != -ENODEV)
 			dev_err(&udev->dev, "device descriptor read/all, error %d\n",
 					retval);
-		if (retval >= 0)
-			retval = -ENOMSG;
 		goto fail;
 	}
+	udev->descriptor = *descr;
+	kfree(descr);
 
 	/*
 	 * Some superspeed devices have finished the link training process
···
 
 
 static int descriptors_changed(struct usb_device *udev,
-		struct usb_device_descriptor *old_device_descriptor,
+		struct usb_device_descriptor *new_device_descriptor,
 		struct usb_host_bos *old_bos)
 {
 	int		changed = 0;
···
 	int		length;
 	char		*buf;
 
-	if (memcmp(&udev->descriptor, old_device_descriptor,
-			sizeof(*old_device_descriptor)) != 0)
+	if (memcmp(&udev->descriptor, new_device_descriptor,
+			sizeof(*new_device_descriptor)) != 0)
 		return 1;
 
 	if ((old_bos && !udev->bos) || (!old_bos && udev->bos))
···
 {
 	struct usb_port *port_dev = hub->ports[port1 - 1];
 	struct usb_device *udev = port_dev->child;
-	struct usb_device_descriptor descriptor;
+	struct usb_device_descriptor *descr;
 	int status = -ENODEV;
-	int retval;
 
 	dev_dbg(&port_dev->dev, "status %04x, change %04x, %s\n", portstatus,
 			portchange, portspeed(hub, portstatus));
···
 			 * changed device descriptors before resuscitating the
 			 * device.
 			 */
-			descriptor = udev->descriptor;
-			retval = usb_get_device_descriptor(udev,
-					sizeof(udev->descriptor));
-			if (retval < 0) {
+			descr = usb_get_device_descriptor(udev);
+			if (IS_ERR(descr)) {
 				dev_dbg(&udev->dev,
-						"can't read device descriptor %d\n",
-						retval);
+						"can't read device descriptor %ld\n",
+						PTR_ERR(descr));
 			} else {
-				if (descriptors_changed(udev, &descriptor,
+				if (descriptors_changed(udev, descr,
 						udev->bos)) {
 					dev_dbg(&udev->dev,
 							"device descriptor has changed\n");
-					/* for disconnect() calls */
-					udev->descriptor = descriptor;
 				} else {
 					status = 0; /* Nothing to do */
 				}
+				kfree(descr);
 			}
 #ifdef CONFIG_PM
 		} else if (udev->state == USB_STATE_SUSPENDED &&

drivers/usb/core/message.c

···
 EXPORT_SYMBOL_GPL(usb_cache_string);
 
 /*
- * usb_get_device_descriptor - (re)reads the device descriptor (usbcore)
- * @dev: the device whose device descriptor is being updated
- * @size: how much of the descriptor to read
+ * usb_get_device_descriptor - read the device descriptor
+ * @udev: the device whose device descriptor should be read
  *
  * Context: task context, might sleep.
- *
- * Updates the copy of the device descriptor stored in the device structure,
- * which dedicates space for this purpose.
  *
  * Not exported, only for use by the core.  If drivers really want to read
  * the device descriptor directly, they can call usb_get_descriptor() with
  * type = USB_DT_DEVICE and index = 0.
  *
- * This call is synchronous, and may not be used in an interrupt context.
- *
- * Return: The number of bytes received on success, or else the status code
- * returned by the underlying usb_control_msg() call.
+ * Returns: a pointer to a dynamically allocated usb_device_descriptor
+ * structure (which the caller must deallocate), or an ERR_PTR value.
  */
-int usb_get_device_descriptor(struct usb_device *dev, unsigned int size)
+struct usb_device_descriptor *usb_get_device_descriptor(struct usb_device *udev)
 {
 	struct usb_device_descriptor *desc;
 	int ret;
 
-	if (size > sizeof(*desc))
-		return -EINVAL;
 	desc = kmalloc(sizeof(*desc), GFP_NOIO);
 	if (!desc)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
-	ret = usb_get_descriptor(dev, USB_DT_DEVICE, 0, desc, size);
+	ret = usb_get_descriptor(udev, USB_DT_DEVICE, 0, desc, sizeof(*desc));
+	if (ret == sizeof(*desc))
+		return desc;
+
 	if (ret >= 0)
-		memcpy(&dev->descriptor, desc, size);
+		ret = -EMSGSIZE;
 	kfree(desc);
-	return ret;
+	return ERR_PTR(ret);
 }
 
 /*

drivers/usb/core/usb.h

···
 		struct usb_endpoint_descriptor *epd);
 extern int usb_remove_device(struct usb_device *udev);
 
-extern int usb_get_device_descriptor(struct usb_device *dev,
-		unsigned int size);
+extern struct usb_device_descriptor *usb_get_device_descriptor(
+		struct usb_device *udev);
 extern int usb_set_isoch_delay(struct usb_device *dev);
 extern int usb_get_bos_descriptor(struct usb_device *dev);
 extern void usb_release_bos_descriptor(struct usb_device *dev);