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Message-ID: <fae7e35a920239fe2a35b6b967bd17e04af1e1b7.camel@hadess.net>
Subject: Re: [PATCH 2/2] usb: Implement usb_revoke() BPF function
From:   Bastien Nocera <hadess@hadess.net>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-usb@vger.kernel.org, bpf@vger.kernel.org,
        Alan Stern <stern@rowland.harvard.edu>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        Peter Hutterer <peter.hutterer@who-t.net>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>
Date:   Tue, 09 Aug 2022 19:27:11 +0200
In-Reply-To: <YvKMVjl6x38Hud6I@kroah.com>
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On Tue, 2022-08-09 at 18:33 +0200, Greg Kroah-Hartman wrote:
> 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.

I can't find any code that would reference
/sys/bus/usb/drivers/usbfs/unbind or /sys/bus/usb/drivers/usbfs wrt
virtio. Where's the host side code for that?

> > 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.

Honestly, I don't understand how this is supposed to work. The USB
device is bound to the usb_generic driver, usbfs doesn't have a link to
the devices it's supposed to handle.