From a2582bd478c13c574d4c16ef1209d333f2a25935 Mon Sep 17 00:00:00 2001 From: Russ Dill Date: Wed, 18 Nov 2009 11:02:13 -0700 Subject: [PATCH] USB: Close usb_find_interface race USB drivers that create character devices call usb_register_dev in their probe function. This associates the usb_interface device with that minor number and creates the character device and announces it to the world. However, the driver's probe function is called before the new usb_interface is added to the driver's klist_devices. This is a problem because userspace will respond to the character device creation announcement by opening the character device. The driver's open function will the call usb_find_interface to find the usb_interface associated with that minor number. usb_find_interface will walk the driver's list of devices and find the usb_interface with the matching minor number. Because the announcement happens before the usb_interface is added to the driver's klist_devices, a race condition exists. A straightforward fix is to walk the list of devices on usb_bus_type instead since the device is added to that list before the announcement occurs. bus_find_device calls get_device to bump the reference count on the found device. It is arguable that the reference count should be dropped by the caller of usb_find_interface instead of usb_find_interface, however, the current users of usb_find_interface do not expect this. Signed-off-by: Russ Dill Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/usb/core/usb.c | 28 ++++++++++------------------ 1 file changed, 10 insertions(+), 18 deletions(-) diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c index b1b85abb9a2d..d1e9440799de 100644 --- a/drivers/usb/core/usb.c +++ b/drivers/usb/core/usb.c @@ -130,24 +130,17 @@ struct usb_host_interface *usb_altnum_to_altsetting( } EXPORT_SYMBOL_GPL(usb_altnum_to_altsetting); -struct find_interface_arg { - int minor; - struct usb_interface *interface; -}; - static int __find_interface(struct device *dev, void *data) { - struct find_interface_arg *arg = data; + int *minor = data; struct usb_interface *intf; if (!is_usb_interface(dev)) return 0; intf = to_usb_interface(dev); - if (intf->minor != -1 && intf->minor == arg->minor) { - arg->interface = intf; + if (intf->minor != -1 && intf->minor == *minor) return 1; - } return 0; } @@ -156,21 +149,20 @@ static int __find_interface(struct device *dev, void *data) * @drv: the driver whose current configuration is considered * @minor: the minor number of the desired device * - * This walks the driver device list and returns a pointer to the interface + * This walks the bus device list and returns a pointer to the interface * with the matching minor. Note, this only works for devices that share the * USB major number. */ struct usb_interface *usb_find_interface(struct usb_driver *drv, int minor) { - struct find_interface_arg argb; - int retval; + struct device *dev; + + dev = bus_find_device(&usb_bus_type, NULL, &minor, __find_interface); + + /* Drop reference count from bus_find_device */ + put_device(dev); - argb.minor = minor; - argb.interface = NULL; - /* eat the error, it will be in argb.interface */ - retval = driver_for_each_device(&drv->drvwrap.driver, NULL, &argb, - __find_interface); - return argb.interface; + return dev ? to_usb_interface(dev) : NULL; } EXPORT_SYMBOL_GPL(usb_find_interface); -- 2.20.1