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Subject: Re: [PATCH] USB: disable all RNDIS protocol drivers
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Oliver Neukum <oneukum@suse.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Enrico Mioso <mrkiko.rs@gmail.com>
Cc:     Jan Engelhardt <jengelh@inai.de>, linux-kernel@vger.kernel.org,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, Kalle Valo <kvalo@kernel.org>,
        Oleksij Rempel <linux@rempel-privat.de>,
        Maciej =?UTF-8?Q?=C5=BBenczykowski?= <maze@google.com>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Andrzej Pietrasiewicz <andrzejtp2010@gmail.com>,
        Jacopo Mondi <jacopo@jmondi.org>,
        =?UTF-8?Q?=C5=81ukasz?= Stelmach <l.stelmach@samsung.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        linux-usb@vger.kernel.org, netdev@vger.kernel.org,
        linux-wireless@vger.kernel.org,
        Ilja Van Sprundel <ivansprundel@ioactive.com>,
        Joseph Tartaro <joseph.tartaro@ioactive.com>
Date:   Wed, 12 Jul 2023 15:00:55 +0200
In-Reply-To: <e5a92f9c-2d56-00fc-5e01-56e7df8dc1c1@suse.com>
References: <20221123124620.1387499-1-gregkh@linuxfoundation.org>
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         <2023070430-fragment-remember-2fdd@gregkh>
         <e5a92f9c-2d56-00fc-5e01-56e7df8dc1c1@suse.com>
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On Wed, 2023-07-12 at 11:22 +0200, Oliver Neukum wrote:
>=20
> 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!!
> > >=20
> > > 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 i=
n routers do use this protocol.
> > >=20
> > > We may also distinguish between these cases and devices you might plu=
g in - as they pose different risk levels.
> >=20
> > 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.

johannes