USB: fix bug in initialization of interface minor numbers

Recent changes in the usbhid layer exposed a bug in usbcore.  If
CONFIG_USB_DYNAMIC_MINORS is enabled then an interface may be assigned
a minor number of 0.  However interfaces that aren't registered as USB
class devices also have their minor number set to 0, during
initialization.  As a result usb_find_interface() may return the
wrong interface, leading to a crash.

This patch (as1418) fixes the problem by initializing every
interface's minor number to -1.  It also cleans up the
usb_register_dev() function, which besides being somewhat awkwardly
written, does not unwind completely on all its error paths.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Philip J. Turmel <philip@turmel.org>
Tested-by: Gabriel Craciunescu <nix.or.die@googlemail.com>
Tested-by: Alex Riesen <raa.lkml@gmail.com>
Tested-by: Matthias Bayer <jackdachef@gmail.com>
CC: Jiri Kosina <jkosina@suse.cz>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/file.c

@@ -159,9 +159,9 @@ void usb_major_cleanup(void)
 int usb_register_dev(struct usb_interface *intf,
 		     struct usb_class_driver *class_driver)
 {
-	int retval = -EINVAL;
+	int retval;
 	int minor_base = class_driver->minor_base;
-	int minor = 0;
+	int minor;
 	char name[20];
 	char *temp;
 
@@ -173,12 +173,17 @@ int usb_register_dev(struct usb_interface *intf,
 	 */
 	minor_base = 0;
 #endif
-	intf->minor = -1;
-
-	dbg ("looking for a minor, starting at %d", minor_base);
 
 	if (class_driver->fops == NULL)
-		goto exit;
+		return -EINVAL;
+	if (intf->minor >= 0)
+		return -EADDRINUSE;
+
+	retval = init_usb_class();
+	if (retval)
+		return retval;
+
+	dev_dbg(&intf->dev, "looking for a minor, starting at %d", minor_base);
 
 	down_write(&minor_rwsem);
 	for (minor = minor_base; minor < MAX_USB_MINORS; ++minor) {
@@ -186,20 +191,12 @@ int usb_register_dev(struct usb_interface *intf,
 			continue;
 
 		usb_minors[minor] = class_driver->fops;
-
-		retval = 0;
+		intf->minor = minor;
 		break;
 	}
 	up_write(&minor_rwsem);
-
-	if (retval)
-		goto exit;
-
-	retval = init_usb_class();
-	if (retval)
-		goto exit;
-
-	intf->minor = minor;
+	if (intf->minor < 0)
+		return -EXFULL;
 
 	/* create a usb class device for this usb interface */
 	snprintf(name, sizeof(name), class_driver->name, minor - minor_base);
@@ -213,11 +210,11 @@ int usb_register_dev(struct usb_interface *intf,
 				      "%s", temp);
 	if (IS_ERR(intf->usb_dev)) {
 		down_write(&minor_rwsem);
-		usb_minors[intf->minor] = NULL;
+		usb_minors[minor] = NULL;
+		intf->minor = -1;
 		up_write(&minor_rwsem);
 		retval = PTR_ERR(intf->usb_dev);
 	}
-exit:
 	return retval;
 }
 EXPORT_SYMBOL_GPL(usb_register_dev);

drivers/usb/core/message.c

@@ -1802,6 +1802,7 @@ free_interfaces:
 		intf->dev.groups = usb_interface_groups;
 		intf->dev.dma_mask = dev->dev.dma_mask;
 		INIT_WORK(&intf->reset_ws, __usb_queue_reset_device);
+		intf->minor = -1;
 		device_initialize(&intf->dev);
 		dev_set_name(&intf->dev, "%d-%s:%d.%d",
 			dev->bus->busnum, dev->devpath,