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

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Date:   Wed, 19 Oct 2022 15:13:34 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Kees Cook <keescook@...omium.org>,
        Mickaël Salaün <mic@...ikod.net>
Cc:     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 Wed, 2022-10-19 at 11:33 -0700, Kees Cook wrote:
> 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.
> 
> This isn't true. If "integrity" is removed from the lsm= line today, IMA
> will immediately panic:
> 
> process_measurement():
>   integrity_inode_get():
>         if (!iint_cache)
>                 panic("%s: lsm=integrity required.\n", __func__);
> 
> and before v5.12 (where the panic was added), it would immediately NULL
> deref. (And it took 3 years to even notice.)

Most people were/are still using the "security=" boot command line
option, not "lsm=".  This previously wasn't a problem with "security=",
but became a problem with "lsm=".  I should have been aware of the
change from "security=" to "lsm=", but unfortunately wasn't.  It took
me totally by surprise.   All of sudden "integrity" went from being a
common IMA/EVM resource to an LSM.  The correct solution would have
been to move it a different initcall.  (It's not too late to fix it.)

-- 
thanks,

Mimi