Re: [PATCH v2] usb: devio: Add ioctl to disallow detaching kernel USB drivers.

[Emilio LÃpez]

Hi BjÃrn,

El 22/01/16 a las 06:41, BjÃrn Mork escribiÃ:
> Emilio LÃpez <emilio.lopez@xxxxxxxxxxxxxxx> writes:
>
> > diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
> > index 38ae877c..bf40aa6 100644
> > --- a/drivers/usb/core/devio.c
> > +++ b/drivers/usb/core/devio.c
> > @@ -77,6 +77,8 @@ struct usb_dev_state {
> >   	unsigned long ifclaimed;
> >   	u32 secid;
> >   	u32 disabled_bulk_eps;
> > +	bool privileges_dropped;
> > +	unsigned long interface_allowed_mask;
> >   };
> >
> >   struct async {
> > @@ -641,6 +643,14 @@ static int claimintf(struct usb_dev_state *ps, unsigned int ifnum)
> >   	if (test_bit(ifnum, &ps->ifclaimed))
> >   		return 0;
> >
> > +	if (ps->privileges_dropped) {
> > +		if (ifnum >= 8*sizeof(ps->interface_allowed_mask))
> > +			return -EINVAL;
>
>
> I don't think you need this runtime test. You can just make sure that
> sizeof(ps->interface_allowed_mask) == sizeof(ps->ifclaimed) at build
> time.
>
> I do find this variable and arbitrary limit a bit confusing, but that's
> not your fault - I guess it is an indication that ifnums > 31 are rare
> :)
>
>
> > diff --git a/include/uapi/linux/usbdevice_fs.h b/include/uapi/linux/usbdevice_fs.h
> > index 019ba1e..9abcb34 100644
> > --- a/include/uapi/linux/usbdevice_fs.h
> > +++ b/include/uapi/linux/usbdevice_fs.h
> > @@ -154,6 +154,10 @@ struct usbdevfs_streams {
> >   	unsigned char eps[0];
> >   };
> >
> > +struct usbdevfs_drop_privs {
> > +	unsigned long interface_allowed_mask;
> > +};
> > +
>
> "unsigned long" isn't a very good choice here, is it?

I went with a type matching ifclaimed on struct usb_dev_state to keep 
the limit the same, but I guess it's not the best idea for an ioctl. I 
can switch it to __u32, keeping the runtime check above as is, or use 
__u64. Which one would you prefer?

Thanks for the review!
Emilio