linux-hardening - Re: [PATCH 2/9] security: Move trivial IMA hooks into LSM

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Date:   Fri, 21 Oct 2022 08:09:06 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     "Dr. Greg" <greg@...ellic.com>, Kees Cook <keescook@...omium.org>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>, Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        Micka?l Sala?n <mic@...ikod.net>, Petr Vorel <pvorel@...e.cz>,
        Borislav Petkov <bp@...e.de>, Takashi Iwai <tiwai@...e.de>,
        Jonathan McDowell <noodles@...com>,
        linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, KP Singh <kpsingh@...nel.org>,
        John Johansen <john.johansen@...onical.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        casey@...aufler-ca.com
Subject: Re: [PATCH 2/9] security: Move trivial IMA hooks into LSM

On 10/21/2022 7:53 AM, Dr. Greg wrote:
> On Wed, Oct 19, 2022 at 11:59:40AM -0700, Kees Cook wrote:
>
> Good morning, I hope the week is ending well for everyone.
>
>> On Wed, Oct 19, 2022 at 10:34:48AM -0400, Mimi Zohar wrote:
>>> The only thing trivial about making IMA and EVM LSMs is moving
>>> them to LSM hooks.  Although static files may be signed and the
>>> signatures distributed with the file data through the normal
>>> distribution mechanisms (e.g. RPM), other files cannot be signed
>>> remotely (e.g.  configuration files).  For these files, both IMA
>>> and EVM may be configured to maintain persistent file state stored
>>> as security xattrs in the form of security.ima file hashes or
>>> security.evm HMACs.  The LSM flexibility of enabling/disabling IMA
>>> or EVM on a per boot basis breaks this usage, potentially
>>> preventing subsequent boots.
>> I'm not suggesting IMA and EVM don't have specific behaviors that
>> need to be correctly integrated into the LSM infrastructure. In
>> fact, I spent a lot of time designing that infrastructure to be
>> flexible enough to deal with these kinds of things. (e.g. plumbing
>> "enablement", etc.) As I mentioned, this was more of trying to
>> provide a head-start on the conversion. I don't intend to drive this
>> -- please take whatever is useful from this example and use it. :)
>> I'm happy to help construct any missing infrastructure needed
>> (e.g. LSM_ORDER_LAST, etc).
> We are 2-3 weeks out from submitting for review and inclusion in the
> kernel, a new LSM, and an associated userspace stack, that will have a
> high degree of significance with respect to these conversations.

Oh, come on, No one likes a teaser trailer. ;)

>
>> Kees Cook
> Best wishes for a pleasant fall weekend.
>
> As always,
>
> Dr. Greg
> The Quixote Project - Flailing at the Travails of Cybersecurity