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Message-ID: <71407e16e141ebc6e9eb042187a1448ad6cfa419.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, 30 Aug 2022 18:28:30 +0200
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On Tue, 2022-08-30 at 17:10 +0200, Greg Kroah-Hartman wrote:
> On Tue, Aug 30, 2022 at 04:44:52PM +0200, Bastien Nocera wrote:
> > On Thu, 2022-08-18 at 17:08 +0200, Greg Kroah-Hartman wrote:
> > > On Tue, Aug 09, 2022 at 07:27:11PM +0200, Bastien Nocera wrote:
> > > > 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?
> > > 
> > > I mean the virtio code uses bind/unbind for it's devices, nothing
> > > to
> > > do
> > > with USB other than the userspace interface involved.
> > 
> > This is one big hammer that is really counterproductive in some
> > fairly
> > common use cases. It's fine for assigning a full USB device to a
> > VM, it
> > really isn't for gently removing "just that bit of interface" the
> > user
> > is using while leaving the rest running.
> 
> In USB, drivers are bound to interfaces, not to the device.

I did implement kernel drivers for devices all the way back in 2020, if
you remember.

> But as Alan pointed out, we don't ever really "bind" the usbfs code
> to
> the interface, so that will not work all that well :(

Right.