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USB: Close usb_find_interface race v3

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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.

The original version of this patch only matched against minor number
instead of driver and minor number. This version matches against both.

Signed-off-by: Russ Dill <Russ.Dill@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Russ Dill 2009-12-14 21:45:35 -07:00 committed by Greg Kroah-Hartman
parent ab7cd8c76c
commit c2d284ee04
1 changed files with 16 additions and 15 deletions
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31
drivers/usb/core/usb.c
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@ -169,7 +169,7 @@ EXPORT_SYMBOL_GPL(usb_altnum_to_altsetting);
struct find_interface_arg {
int minor;
struct usb_interface *interface;
struct device_driver *drv;
};
static int __find_interface(struct device *dev, void *data)
@ -180,12 +180,10 @@ static int __find_interface(struct device *dev, void *data)
if (!is_usb_interface(dev))
return 0;
if (dev->driver != arg->drv)
return 0;
intf = to_usb_interface(dev);
if (intf->minor != -1 && intf->minor == arg->minor) {
arg->interface = intf;
return 1;
}
return 0;
return intf->minor == arg->minor;
}
/**
@ -193,21 +191,24 @@ 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
* with the matching minor. Note, this only works for devices that share the
* USB major number.
* This walks the bus device list and returns a pointer to the interface
* with the matching minor and driver. 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;
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;
argb.drv = &drv->drvwrap.driver;
dev = bus_find_device(&usb_bus_type, NULL, &argb, __find_interface);
/* Drop reference count from bus_find_device */
put_device(dev);
return dev ? to_usb_interface(dev) : NULL;
}
EXPORT_SYMBOL_GPL(usb_find_interface);