linux-kernel - Re: [PATCH] USB: disable all RNDIS protocol drivers

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Message-ID: <CADvTj4q3mMyymD1wDCFv6djJ1SGOLaikWnTsNVJJEPf7GdoUvw@mail.gmail.com>
Date:   Tue, 10 Jan 2023 15:47:59 -0700
From:   James Hilliard <james.hilliard1@...il.com>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Kalle Valo <kvalo@...nel.org>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Maciej Żenczykowski <maze@...gle.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Andrzej Pietrasiewicz <andrzejtp2010@...il.com>,
        Jacopo Mondi <jacopo@...ndi.org>,
        Łukasz Stelmach <l.stelmach@...sung.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        linux-usb@...r.kernel.org, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org,
        Ilja Van Sprundel <ivansprundel@...ctive.com>,
        Joseph Tartaro <joseph.tartaro@...ctive.com>
Subject: Re: [PATCH] USB: disable all RNDIS protocol drivers

On Tue, Jan 10, 2023 at 3:32 PM Johannes Berg <johannes@...solutions.net> wrote:
>
> On Wed, 2022-11-23 at 16:05 +0100, Greg Kroah-Hartman wrote:
> > On Wed, Nov 23, 2022 at 03:20:36PM +0100, Johannes Berg wrote:
> > > On Wed, 2022-11-23 at 13:46 +0100, Greg Kroah-Hartman wrote:
> > > > The Microsoft RNDIS protocol is, as designed, insecure and vulnerable on
> > > > any system that uses it with untrusted hosts or devices.  Because the
> > > > protocol is impossible to make secure, just disable all rndis drivers to
> > > > prevent anyone from using them again.
> > > >
> > >
> > > Not that I mind disabling these, but is there any more detail available
> > > on this pretty broad claim? :)
> >
> > I don't want to get into specifics in public any more than the above.
>
> Fair.

I would guess it's related to?:
https://github.com/torvalds/linux/commit/c7dd13805f8b8fc1ce3b6d40f6aff47e66b72ad2

>
> > The protocol was never designed to be used with untrusted devices.  It
> > was created, and we implemented support for it, when we trusted USB
> > devices that we plugged into our systems, AND we trusted the systems we
> > plugged our USB devices into.  So at the time, it kind of made sense to
> > create this, and the USB protocol class support that replaced it had not
> > yet been released.
> >
> > As designed, it really can not work at all if you do not trust either
> > the host or the device, due to the way the protocol works.  And I can't
> > see how it could be fixed if you wish to remain compliant with the
> > protocol (i.e. still work with Windows XP systems.)

Can it be fixed in a way that most RNDIS based modems devices like
RNDIS based android tethering work with Linux based hosts still?

>
> I guess I just don't see how a USB-based protocol can be fundamentally
> insecure (to the host), when the host is always in control over messages
> and parses their content etc.?
>
> I can see this with e.g. firewire which must allow DMA access, and now
> with Thunderbolt we have the same and ended up with boltd, but USB?
>
> > Today, with untrusted hosts and devices, it's time to just retire this
> > protcol.  As I mentioned in the patch comments, Android disabled this
> > many years ago in their devices, with no loss of functionality.
>
> I'm not sure Android counts that much, FWIW, at least for WiFi there
> really is no good reason to plug in a USB WiFi dongle into an Android
> phone, and quick googling shows that e.g. Android TV may - depending on
> build - support/permit RNDIS Ethernet?
>
> Anyway, there was probably exactly one RNDIS WiFi dongle from Broadcom
> (for some kind of console IIRC), so it's not a huge loss. Just having
> issues with the blanket statement that a USB protocol can be designed as
> inscure :)
>
> johannes
>