linux-kernel - Re: [PATCH 04/11] S.A.R.A. USB Filtering

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Date:   Tue, 20 Jun 2017 09:07:21 +0200
From:   Pavel Machek <pavel@....cz>
To:     Salvatore Mesoraca <s.mesoraca16@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        kernel-hardening@...ts.openwall.com,
        Brad Spengler <spender@...ecurity.net>,
        PaX Team <pageexec@...email.hu>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Kees Cook <keescook@...omium.org>,
        James Morris <james.l.morris@...cle.com>,
        "Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: [PATCH 04/11] S.A.R.A. USB Filtering

On Mon 2017-06-12 18:56:53, Salvatore Mesoraca wrote:
> Introduction of S.A.R.A. USB Filtering.
> It uses the "usb_device_auth" LSM hook to provide a mechanism to decide
> which USB devices should be authorized to connect to the system and
> which shouldn't.
> The main goal is to narrow the attack surface for custom USB devices
> designed to exploit vulnerabilities found in some USB device drivers.
> Via configuration it's possible to allow or to deny authorization, based
> on one or more of: Vendor ID, Product ID, bus name and port number. There
> is also support for "trailing wildcards".

Hmm. Given that USB device provides vendor id/product id, this does
not really stop anyone, right?

AFAICT you can still get USB stick with vid/pid of logitech keyboard,
and kernel will recognize it as a usb stick.

So you should not really filter on vid/pid, but on device
types (sha sum of USB descriptor?).

> Depending on the configuration, it can work both as a white list or as a
> black list.

Blacklisting vid/pid is completely useless. Whitelisting vid/pid is
nearly so. Attacker able to plug USB devices sees devices already
attached, so he can guess right vid/pids quite easily.

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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