linux-kernel - Re: [PATCH] selinux: add selinux_is

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Date:   Wed, 12 Apr 2017 12:33:18 -0400
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     Sebastien Buisson <sbuisson.ddn@...il.com>
Cc:     Paul Moore <pmoore@...hat.com>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, selinux@...ho.nsa.gov,
        william.c.roberts@...el.com, serge@...lyn.com,
        james.l.morris@...cle.com, Eric Paris <eparis@...isplace.org>,
        Paul Moore <paul@...l-moore.com>,
        Sebastien Buisson <sbuisson@....com>
Subject: Re: [PATCH] selinux: add selinux_is_enforced() function

On Wed, 2017-04-12 at 17:19 +0200, Sebastien Buisson wrote:
> 2017-04-12 15:58 GMT+02:00 Stephen Smalley <sds@...ho.nsa.gov>:
> > Even your usage of selinux_is_enabled() looks suspect; that should
> > probably go away.  Only other user of it seems to be some cred
> > validity
> > checking that could be dropped as well.
> 
> Well the main reason for calling selinux_is_enabled() is performance
> optimization.
> Should I propose a patch to add a new security_is_enabled() function
> at the LSM abstraction layer? Or do you consider we should not test
> security enabled at all?

It isn't clear what "is enabled" means in general, particularly with
stacking. I would either drop it or replace it with a LSM hook that is
more precise.  For example, NFSv4 introduced a security_ismaclabel()
hook so that it could test whether a given security.* xattr is a MAC
label.