diff options
author | Russ Dill <Russ.Dill@gmail.com> | 2009-12-14 21:45:35 -0700 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@suse.de> | 2009-12-15 07:50:28 -0800 |
commit | c2d284ee04ab6f6718de2ddcf1b43160e046c41d (patch) | |
tree | 915ff77064dd9c6c002f416d2b1ead97d1c7c970 | |
parent | ab7cd8c76cb47f1bda0ad964d309b4efce81b5e9 (diff) |
USB: Close usb_find_interface race v3
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>
-rw-r--r-- | drivers/usb/core/usb.c | 31 |
1 files changed, 16 insertions, 15 deletions
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c index 932f68e6ad1..d86276c639c 100644 --- a/drivers/usb/core/usb.c +++ b/drivers/usb/core/usb.c @@ -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); |