Re: [PATCH 2/2] usb: Implement usb_revoke() BPF function

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Aug 09, 2022 at 04:31:04PM +0200, Bastien Nocera wrote:
> On Tue, 2022-08-09 at 12:38 +0200, Greg Kroah-Hartman wrote:
> > Now if you really really want to disable a device from under a user,
> > without the file handle present, you can do that today, as root, by
> > doing the 'unbind' hack through userspace and sysfs.  It's so common
> > that this seems to be how virtual device managers handle virtual
> > machines, so it should be well tested by now.
> 
> The only thing I know that works that way is usbip, and it requires
> unbinding each of the interfaces:
> 
> https://sourceforge.net/p/usbip/git-windows/ci/master/tree/trunk/userspace/src/bind-driver.c#l157

virtio devices also use the api from what I recall.

> That means that, for example, revoking access to the raw USB device
> that OpenRGB used to blink colours across a keyboard would disconnect
> the keyboard from the HID device.

No, you unbind the usbfs driver, not the hid driver.

> Can you show me any other users of that "trick" that would keep the
> "hid" keyboard driver working while access to the /dev/bus/usb/* device
> node is revoked/closed/yanked/unbound?

Try unbinding usbfs from the device instead.

> And if you can't, I would appreciate some efforts being made trying to
> understand the use case, along with the limitations we're working
> against, so we can find a good solution to the problem, instead of
> retreading discussion points.

As you have not documented the use case well enough in these changelog
entries for me to understand it, the fact that I brought up things you
previously discussed seems to mean you didn't document it well enough
here for it not to come up again :)

thanks,

greg k-h