On Wed, Nov 18, 2009 at 11:02:13AM -0700, Russ Dill wrote: > 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> > --- > drivers/usb/core/usb.c | 30 +++++++++++------------------- > 1 files changed, 11 insertions(+), 19 deletions(-) Looks good, thanks for finding and fixing this. I'll queue it up. greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
