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Date:   Wed, 19 Oct 2022 11:33:38 -0700
From:   Kees Cook <keescook@chromium.org>
To:     =?iso-8859-1?Q?Micka=EBl_Sala=FCn?= <mic@digikod.net>
Cc:     Mimi Zohar <zohar@linux.ibm.com>, Paul Moore <paul@paul-moore.com>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
        linux-security-module@vger.kernel.org,
        linux-integrity@vger.kernel.org, KP Singh <kpsingh@kernel.org>,
        Casey Schaufler <casey@schaufler-ca.com>,
        John Johansen <john.johansen@canonical.com>,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH 1/9] integrity: Prepare for having "ima" and "evm"
 available in "integrity" LSM
Message-ID: <202210191129.BFBF8035@keescook>
References: <20221013222702.never.990-kees@kernel.org>
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 <08a8b202-69b4-e154-28f5-337a898acf61@digikod.net>
 <202210141050.A8DF7D10@keescook>
 <0d2b9d34-2eda-8aa6-d596-eb1899645192@digikod.net>
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On Mon, Oct 17, 2022 at 11:26:44AM +0200, Micka?l Sala?n wrote:
> 
> On 14/10/2022 19:59, Kees Cook wrote:
> > On Fri, Oct 14, 2022 at 04:40:01PM +0200, Micka?l Sala?n 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.)

-- 
Kees Cook