Re: [PATCH 05/17] USB: Lock registered interfaces during manual driver binding

[Leon Romanovsky]

On Thu, Nov 05, 2026 at 12:24:33PM -0500, Alan Stern wrote:
> On Thu, Nov 05, 2026 at 01:42:18PM +0200, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@xxxxxxxxxx>
> > 
> > Interface claims hold the USB device lock, but device_bind_driver()
> > requires the target interface lock. Without it, trust-policy writes can
> > race admission.
> 
> This says nothing about usb_driver_release_refused_claim() and the code 
> related to it.  It is an incomplete description of the patch.
> 
> Note that nothing prevents drivers from using an interface they claim 
> before that interface is registered.  For your scheme to work properly, 
> you should make sure the claim is authorized when 
> usb_driver_claim_interface() is called, not when the interface is 
> registered.

This patch is unrelated to authorization; it ensures that the lock is
acquired when the driver is bound. The authorization flow will be handled
separately, as discussed here.
https://lore.kernel.org/linux-pci/20261105-device-trust-core-v1-0-1e536825b4eb@xxxxxxxxxx/T/#mb66dc792d2b8e5089df40ea8f08824e7d451088a

Thanks

> 
> Alan Stern
> 
> > +/*
> > + * The driver core refused to bind an interface that a sibling claimed before
> > + * it was registered, and dropped the claim. Let the claimant release the
> > + * interface instead of operating it with a bound interface but no driver.
> > + */
> > +void usb_driver_release_refused_claim(struct usb_interface *iface,
> > +				      struct device_driver *claimant)
> > +{
> > +	struct device *dev = &iface->dev;
> > +
> > +	device_lock(dev);
> > +	if (!dev->driver && iface->condition == USB_INTERFACE_BOUND) {
> > +		dev->driver = claimant;
> > +		usb_unbind_interface(dev);
> > +		dev_set_drvdata(dev, NULL);
> > +		dev->driver = NULL;
> > +	}
> > +	device_unlock(dev);
> > +}
> > +
> >  /* returns 0 if no match, 1 if match */
> >  int usb_match_device(struct usb_device *dev, const struct usb_device_id *id)
> >  {
> > diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
> > index a738d03c23eac..d35a7710c8ef4 100644
> > --- a/drivers/usb/core/message.c
> > +++ b/drivers/usb/core/message.c
> > @@ -2264,6 +2264,7 @@ int usb_set_configuration(struct usb_device *dev, int configuration)
> >  	 */
> >  	for (i = 0; i < nintf; ++i) {
> >  		struct usb_interface *intf = cp->interface[i];
> > +		struct device_driver *claimant;
> >  
> >  		if (intf->dev.of_node &&
> >  		    !of_device_is_available(intf->dev.of_node)) {
> > @@ -2277,7 +2278,14 @@ int usb_set_configuration(struct usb_device *dev, int configuration)
> >  			dev_name(&intf->dev), configuration,
> >  			intf->cur_altsetting->desc.bInterfaceNumber);
> >  		device_enable_async_suspend(&intf->dev);
> > +		claimant = intf->dev.driver;
> > +		if (claimant && !try_module_get(claimant->owner))
> > +			claimant = NULL;
> >  		ret = device_add(&intf->dev);
> > +		if (!ret && claimant && !intf->dev.driver)
> > +			usb_driver_release_refused_claim(intf, claimant);
> > +		if (claimant)
> > +			module_put(claimant->owner);
> >  		if (ret != 0) {
> >  			dev_err(&dev->dev, "device_add(%s) --> %d\n",
> >  				dev_name(&intf->dev), ret);
> > diff --git a/drivers/usb/core/usb.h b/drivers/usb/core/usb.h
> > index a9b37aeb515be..293340a48b6c5 100644
> > --- a/drivers/usb/core/usb.h
> > +++ b/drivers/usb/core/usb.h
> > @@ -49,6 +49,8 @@ extern int usb_set_isoch_delay(struct usb_device *dev);
> >  extern int usb_get_bos_descriptor(struct usb_device *dev);
> >  extern void usb_release_bos_descriptor(struct usb_device *dev);
> >  extern int usb_set_configuration(struct usb_device *dev, int configuration);
> > +void usb_driver_release_refused_claim(struct usb_interface *iface,
> > +				      struct device_driver *claimant);
> >  extern int usb_choose_configuration(struct usb_device *udev);
> >  extern int usb_generic_driver_probe(struct usb_device *udev);
> >  extern void usb_generic_driver_disconnect(struct usb_device *udev);
> > 
> > -- 
> > 2.56.0