linux-kernel - Re: [PATCH 3/6] firmware: differentiate between signed regulatory.db and other firmware

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Message-Id: <1526014826.3414.46.camel@linux.vnet.ibm.com>
Date:   Fri, 11 May 2018 01:00:26 -0400
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Matthew Garrett <mjg59@...f.ucam.org>,
        Peter Jones <pjones@...hat.com>,
        "AKASHI, Takahiro" <takahiro.akashi@...aro.org>,
        David Howells <dhowells@...hat.com>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Kalle Valo <kvalo@...eaurora.org>,
        Seth Forshee <seth.forshee@...onical.com>,
        Johannes Berg <johannes.berg@...el.com>,
        linux-integrity@...r.kernel.org,
        Hans de Goede <hdegoede@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andres Rodriguez <andresx7@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH 3/6] firmware: differentiate between signed
 regulatory.db and other firmware

On Thu, 2018-05-10 at 23:26 +0000, Luis R. Rodriguez wrote:
> On Wed, May 09, 2018 at 10:00:58PM -0400, Mimi Zohar wrote:
> > On Wed, 2018-05-09 at 23:48 +0000, Luis R. Rodriguez wrote:
> > > On Wed, May 09, 2018 at 06:06:57PM -0400, Mimi Zohar wrote:
> > 
> > > > > > Yes, writing regdb as a micro/mini LSM sounds reasonable.  The LSM
> > > > > > would differentiate between other firmware and the regulatory.db based
> > > > > > on the firmware's pathname.
> > > > > 
> > > > > If that is the only way then it would be silly to do the mini LSM as all
> > > > > calls would have to have the check. A special LSM hook for just the
> > > > > regulatory db also doesn't make much sense.
> > > > 
> > > > All calls to request_firmware() are already going through this LSM
> > > > hook.  I should have said, it would be based on both READING_FIRMWARE
> > > > and the firmware's pathname.
> > > 
> > > Yes, but it would still be a strcmp() computation added for all
> > > READING_FIRMWARE. In that sense, the current arrangement is only open coding the
> > > signature verification for the regulatory.db file.  One way to avoid this would
> > > be to add an LSM specific to the regulatory db
> > 
> > Casey already commented on this suggestion.
> 
> Sorry but I must have missed this, can you send me the email or URL where he did that?
> I never got a copy of that email I think.

My mistake.  I've posted similar patches for kexec_load and for the
firmware sysfs fallback, both call security_kernel_read_file().
Casey's comment was in regards to kexec_load[1], not for the sysfs
fallback mode.  Here's the link to the most recent version of the
kexec_load patches.[2]

[1] http://kernsec.org/pipermail/linux-security-module-archive/2018-May/006690.html
[2] http://kernsec.org/pipermail/linux-security-module-archive/2018-May/006854.html

Mimi