Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20221025184519.13231-1-casey@schaufler-ca.com>
 <20221025184519.13231-3-casey@schaufler-ca.com> <Y1jMeWl0oV4/2zyE@kroah.com>
 <5396ab1e-9b93-df33-ca49-58dc59459a76@schaufler-ca.com> <Y1olsHWnaEk6+b1L@kroah.com>
 <612c169c-2e11-13cf-9742-19714a247152@schaufler-ca.com> <CAHC9VhR8_aQFxBq4fG=q8FgVUEZAL6F_iSE9kFnO7Mf4tf52AQ@mail.gmail.com>
 <20cdb098-400e-25d0-f93e-98efb1095b68@schaufler-ca.com>
In-Reply-To: <20cdb098-400e-25d0-f93e-98efb1095b68@schaufler-ca.com>
From:   Paul Moore <paul@paul-moore.com>
Date:   Wed, 9 Nov 2022 21:37:48 -0500
Message-ID: <CAHC9VhR50=d_pjoxOMX_a8oyKc572BqjJUZD5Mcd8snHHq5WHQ@mail.gmail.com>
Subject: Re: [PATCH v1 2/8] LSM: Add an LSM identifier for external use
To:     Casey Schaufler <casey@schaufler-ca.com>
Cc:     Greg KH <gregkh@linuxfoundation.org>, casey.schaufler@intel.com,
        linux-security-module@vger.kernel.org, jmorris@namei.org,
        keescook@chromium.org, john.johansen@canonical.com,
        penguin-kernel@i-love.sakura.ne.jp, stephen.smalley.work@gmail.com,
        linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        mic@digikod.net
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Wed, Nov 9, 2022 at 7:57 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
> On 11/9/2022 3:33 PM, Paul Moore wrote:

...

> >   My reason for
> > doing so is rather simple, we're going to treat the ID as a 32-bit
> > value so we have *plenty* of room (just the thought of supporting +4
> > billion unique LSMs is comically insane), and I'd like to try and
> > leave some space for yet-undetermined "special" things that we might
> > need to convey in the LSM syscalls.  For example, this would allow us
> > to convey additional information to userspace when an application
> > asked for labeling information using one of these reserved LSM IDs;
> > applications which did not know (or care) about the special ID would
> > continue to function normally but augmented/new applications would be
> > able to make sense of the additional information ... and we wouldn't
> > have to add a new syscall to do it.
>
> I don't see how
>
>         #define LSM_ID_SPECIAL  2
>
> is better than
>
>         #define LSM_ID_SPECIAL  13
>
> There's no reason to "group" LSM_ID values, nor have a range of them.
> Really, I don't care one way or the other. I will bend to whatever will
> is stronger.

The token values are not intended to be grouped in any sort of range,
it is just easier to say values 0-32 are reserved that create 33 macro
defines like LSM_ID_RESERVED1..LSM_ID_RESERVED32.  The actual token
values shouldn't really mean anything, we could randomly assign them
if that helps get my point across, I just want a few reserved numbers
in the token space to leave room for future unknowns.

It's not like I'm suggesting something that has never been done before :)

-- 
paul-moore.com