Re: [PATCH v3] usb: devio: Add ioctl to disallow detaching kernel USB drivers.

[Emilio LÃpez]

Hello Alan,

El 04/02/16 a las 13:27, Alan Stern escribiÃ:
> On Thu, 4 Feb 2016, Emilio LÃpez wrote:
>
> > From: Reilly Grant <reillyg@xxxxxxxxxxxx>
> >
> > The new USBDEVFS_DROP_PRIVILEGES ioctl allows a process to voluntarily
> > relinquish the ability to issue other ioctls that may interfere with
> > other processes and drivers that have claimed an interface on the
> > device.
> >
> > Signed-off-by: Reilly Grant <reillyg@xxxxxxxxxxxx>
> > Signed-off-by: Emilio LÃpez <emilio.lopez@xxxxxxxxxxxxxxx>
> >
> > ---
> >
> > Changes in v3:
> > - Switch ioctl to use a __u32 given the iface qty is capped at 32
> > - Reword comments as requested by Alan
> > - Allow callers to shrink the allowed interfaces mask
>
> > @@ -624,6 +626,10 @@ static int claimintf(struct usb_dev_state *ps, unsigned int ifnum)
> >   	if (test_bit(ifnum, &ps->ifclaimed))
> >   		return 0;
> >
> > +	if (ps->privileges_dropped
> > +	 && !test_bit(ifnum, &ps->interface_allowed_mask))
>
> Continuation lines in this file are indented by 2 tab stops, not 1
> space.

Ok, I'll change it.

> > @@ -1198,6 +1202,27 @@ static int proc_connectinfo(struct usb_dev_state *ps, void __user *arg)
> >
> >   static int proc_resetdevice(struct usb_dev_state *ps)
> >   {
> > +	struct usb_host_config *actconfig = ps->dev->actconfig;
> > +	struct usb_interface *interface;
> > +	int i, number;
> > +
> > +	/* Don't allow a device reset if the process has dropped the
> > +	 * privilege to do such things and any of the interfaces are
> > +	 * currently claimed.
> > +	 */
> > +	if (ps->privileges_dropped && actconfig) {
> > +		for (i = 0; i < actconfig->desc.bNumInterfaces; ++i) {
> > +			interface = actconfig->interface[i];
> > +			number = interface->cur_altsetting->desc.bInterfaceNumber;
> > +			if (usb_interface_claimed(interface)) {
>
> The test should be:
>
> 			if (usb_interface_claimed(interface) &&
> 					!test_bit(number, &ps->ifclaimed)) {
>
> We don't want to prevent people from resetting a device merely because
> they have claimed an interface.  Only if someone else has claimed one.

Sounds sensible, now changed as well.

> > +				dev_warn(&ps->dev->dev,
> > +					"usbfs: interface %d claimed by %s while '%s' resets device\n",
> > +					number,	interface->dev.driver->name, current->comm);
> > +				return -EACCES;
> > +			}
> > +		}
> > +	}
> > +
> >   	return usb_reset_device(ps->dev);
> >   }
>
> Also, it wouldn't hurt to change proc_get_capabilities() and
> include/uapi/linux/usbdevicefs.h to add a USBDEVFS_CAP_DROP_PRIVILEGES
> bit.

Good idea, I've added a bit now. I'm writing some docs and polishing a 
program to test this as Greg requested and I'll submit v4 then.

Thanks!
Emilio