From: Russ Dill <russ.dill@xxxxxxxxx>
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 <Russ.Dill@xxxxxxxxx>
Cc: stable <stable@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
---
drivers/usb/core/usb.c | 30 +++++++++++-------------------
1 files changed, 11 insertions(+), 19 deletions(-)
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
index b1b85ab..d1e9440 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);
--
1.6.5.5
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