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

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Date:   Thu, 13 Jul 2023 02:28:26 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Oliver Neukum <oneukum@...e.com>,
        Enrico Mioso <mrkiko.rs@...il.com>,
        Jan Engelhardt <jengelh@...i.de>, 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 Wed, 2023-07-12 at 18:39 +0200, Greg Kroah-Hartman wrote:
> On Wed, Jul 12, 2023 at 03:00:55PM +0200, Johannes Berg wrote:
> > On Wed, 2023-07-12 at 11:22 +0200, Oliver Neukum wrote:
> > > 
> > > On 04.07.23 08:47, Greg Kroah-Hartman wrote:
> > > > On Mon, Jul 03, 2023 at 11:11:57PM +0200, Enrico Mioso wrote:
> > > > > Hi all!!
> > > > > 
> > > > > I think the rndis_host USB driver might emit a warning in the dmesg, but disabling the driver wouldn't be a good idea.
> > > > > The TP-Link MR6400 V1 LTE modem and also some ZTE modems integrated in routers do use this protocol.
> > > > > 
> > > > > We may also distinguish between these cases and devices you might plug in - as they pose different risk levels.
> > > > 
> > > > Again, you have to fully trust the other side of an RNDIS connection,
> > > > any hints on how to have the kernel determine that?
> > 
> > > it is a network protocol. So this statement is kind of odd.
> > > Are you saying that there are RNDIS messages that cannot be verified
> > > for some reason, that still cannot be disclosed?
> > 
> > Agree, it's also just a USB device, so no special trickery with DMA,
> > shared buffers, etc.
> > 
> > I mean, yeah, the RNDIS code is really old and almost certainly has a
> > severe lack of input validation, but that still doesn't mean it's
> > fundamentally impossible.
> 
> You all are going to make me have to write some exploits aren't you...

This is getting a bit childish. Nobody ever said that wasn't possible,
in fact I did say exactly above that I'm sure since it's old and all it
lacks input validation. So yeah, I full well believe that you can write
exploits for it.

All we said is that your statement of "RNDIS is fundamentally unfixable"
doesn't make a lot of sense. If this were the case, all USB drivers
would have to "trust the other side" as well, right?

johannes