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

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Date:   Mon, 17 Oct 2022 11:26:44 +0200
From:   Mickaël Salaün <mic@...ikod.net>
To:     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>,
        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 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).


> 
>> 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.