linux-kernel - Re: [PATCH v3 1/1] security: Add CONFIG_LSM_AUTO to handle default LSM stack ordering

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Date:   Fri, 4 Nov 2022 17:29:15 +0100
From:   Mickaël Salaün <mic@...ikod.net>
To:     Paul Moore <paul@...l-moore.com>, Kees Cook <keescook@...omium.org>
Cc:     Casey Schaufler <casey@...aufler-ca.com>,
        Nicolas Iooss <nicolas.iooss@....org>,
        James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Mickaël Salaün <mic@...ux.microsoft.com>
Subject: Re: [PATCH v3 1/1] security: Add CONFIG_LSM_AUTO to handle default
 LSM stack ordering


On 18/10/2022 21:31, Paul Moore wrote:
> On Tue, Oct 18, 2022 at 1:55 AM Kees Cook <keescook@...omium.org> wrote:
>> On Mon, Oct 17, 2022 at 09:45:21PM -0400, Paul Moore wrote:

[...]

>>> We can have defaults, like we do know, but I'm in no hurry to remove
>>> the ability to allow admins to change the ordering at boot time.
>>
>> My concern is with new LSMs vs the build system. A system builder will
>> be prompted for a new CONFIG_SECURITY_SHINY, but won't be prompted
>> about making changes to CONFIG_LSM to include it.
> 
> I would argue that if an admin/builder doesn't understand what a shiny
> new LSM does, they shouldn't be enabling that shiny new LSM.  Adding
> new, potentially restrictive, controls to your kernel build without a
> basic understanding of those controls is a recipe for disaster and I
> try to avoid recommending disaster as a planned course of action :)

It depends on what this shiny new LSMs do *by default*. In the case of 
Landlock, it do nothing unless a process does specific system calls 
(same as for most new kernel features: sysfs entries, syscall flags…). I 
guess this is the same for most LSMs.