linux-kernel - Re: [PATCH 10/10] LSM: Blob sharing support for S.A.R.A and LandLock

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Date:   Thu, 13 Sep 2018 22:42:59 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     keescook@...omium.org
Cc:     casey@...aufler-ca.com, linux-security-module@...r.kernel.org,
        James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
        selinux@...ho.nsa.gov, john.johansen@...onical.com,
        penguin-kernel@...ove.sakura.ne.jp,
        Stephen Smalley <sds@...ho.nsa.gov>,
        linux-fsdevel@...r.kernel.org, adobriyan@...il.com,
        casey.schaufler@...el.com
Subject: Re: [PATCH 10/10] LSM: Blob sharing support for S.A.R.A and LandLock

On Thu, Sep 13, 2018 at 5:52 PM Kees Cook <keescook@...omium.org> wrote:
> On Thu, Sep 13, 2018 at 2:38 PM, Paul Moore <paul@...l-moore.com> wrote:
> > The infrastructure bits aren't really my concern; in fact I *like*
> > that the infrastructure is always exercised, it makes
> > testing/debugging easier.  I also like the ability to limit the
> > user/admin to one LSM at boot time to make support easier; my goal is
> > to allow a distro to build support for multiple LSMs without also
> > requiring that distro to support *stacked* LSMs
>
> I see your point, but as soon as SARA and Landlock appear, they'll have:
>
>     depends on SECURITY_STACKING
>
> and then all distros will enable it and there will be no sensible
> runtime way to manage it. If, instead, we make it entirely runtime
> now, then a CONFIG can control the default state and we can provide
> guidance to how SARA and Landlock should expose their "enable"ness.

I question why SARA and LandLock require stacking.  While some LSMs
may benefit from stacking, e.g. Yama, traditionally each LSM has been
able to stand on its own.  I think this is a quality that should be
preserved.

> > (see my earlier
> > comments about the difficulty in determining the source of a failed
> > operation).
>
> Agreed. I would hope that audit could help for that case. *stare at blue sky*

*also staring at blue sky*

Audit can help, but it is independent of the LSMs and not a hard
requirement for all, and even when it is enabled the config might not
be suitable to provide enough information to be helpful in this case.

-- 
paul moore
www.paul-moore.com