linux-kernel - Re: [PATCH 1/9] integrity: Prepare for having "ima" and "evm" available in "integrity" LSM

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Message-ID: <202210171101.2E96A7D557@keescook>
Date:   Mon, 17 Oct 2022 11:11:01 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Mickaël Salaün <mic@...ikod.net>
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>,
        linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, KP Singh <kpsingh@...nel.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        John Johansen <john.johansen@...onical.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 1/9] integrity: Prepare for having "ima" and "evm"
 available in "integrity" LSM

On Mon, Oct 17, 2022 at 11:26:44AM +0200, Mickaël Salaün wrote:
> 
> On 14/10/2022 19:59, Kees Cook wrote:
> > On Fri, Oct 14, 2022 at 04:40:01PM +0200, Mickaël Salaün wrote:
> > > This is not backward compatible
> > 
> > Why? Nothing will be running LSM hooks until init finishes, at which
> > point the integrity inode cache will be allocated. And ima and evm don't
> > start up until lateinit.
> > 
> > > , but can easily be fixed thanks to
> > > DEFINE_LSM().order
> > 
> > That forces the LSM to be enabled, which may not be desired?
> 
> This is not backward compatible because currently IMA is enabled
> independently of the "lsm=" cmdline, which means that for all installed
> systems using IMA and also with a custom "lsm=" cmdline, updating the kernel
> with this patch will (silently) disable IMA. Using ".order =
> LSM_ORDER_FIRST," should keep this behavior.
> 
> BTW, I think we should set such order (but maybe rename it) for LSMs that do
> nothing unless configured (e.g. Yama, Landlock).

Ah yeah, good point. the .enabled stuff will need to be correctly wired
up. Anyway, it's a good starting point for the conversion, so I'm hoping
it can be carried forward by someone who is not me. :) (Hint hint to the
integrity folks...)

> > > Side node: I proposed an alternative to that but it was Nacked:
> > > https://lore.kernel.org/all/20210222150608.808146-1-mic@digikod.net/
> > 
> > Yeah, for the reasons pointed out -- that can't work. The point is to
> > not have The Default LSM. I do think Casey's NAK was rather prickly,
> > though. ;)
> 
> I don't agree, there is no "the default LSM", and this new behavior is under
> an LSM_AUTO configuration option.

The "config it twice" aspect of the current situation is suboptimal,
yes. Let me go comment on the old thread...

-- 
Kees Cook