Re: [PATCH v1 2/8] LSM: Add an LSM identifier for external use

From: Paul Moore <paul@paul-moore.com>
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
Subject: Re: [PATCH v1 2/8] LSM: Add an LSM identifier for external use
Date: Wed, 9 Nov 2022 21:37:48 -0500	[thread overview]
Message-ID: <CAHC9VhR50=d_pjoxOMX_a8oyKc572BqjJUZD5Mcd8snHHq5WHQ@mail.gmail.com> (raw)
In-Reply-To: <20cdb098-400e-25d0-f93e-98efb1095b68@schaufler-ca.com>

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