linux-kernel - Re: [PATCH v3 1/9] LSM: Identify modules by more than name

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Message-ID: <CAHC9VhR9h1GF6VGovp1+UB-vt+QNofjmecPwLqE3OviKQHRMcg@mail.gmail.com>
Date:   Sun, 27 Nov 2022 22:48:53 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Mickaël Salaün <mic@...ikod.net>,
        Casey Schaufler <casey@...aufler-ca.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, casey.schaufler@...el.com,
        linux-security-module@...r.kernel.org, jmorris@...ei.org,
        keescook@...omium.org, john.johansen@...onical.com,
        penguin-kernel@...ove.sakura.ne.jp, stephen.smalley.work@...il.com,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH v3 1/9] LSM: Identify modules by more than name

On Fri, Nov 25, 2022 at 11:19 AM Mickaël Salaün <mic@...ikod.net> wrote:
> On 24/11/2022 06:40, Greg KH wrote:
> > On Wed, Nov 23, 2022 at 12:15:44PM -0800, Casey Schaufler wrote:
> >> Create a struct lsm_id to contain identifying information
> >> about Linux Security Modules (LSMs). At inception this contains
> >> the name of the module and an identifier associated with the
> >> security module. Change the security_add_hooks() interface to
> >> use this structure. Change the individual modules to maintain
> >> their own struct lsm_id and pass it to security_add_hooks().
> >>
> >> The values are for LSM identifiers are defined in a new UAPI
> >> header file linux/lsm.h. Each existing LSM has been updated to
> >> include it's LSMID in the lsm_id.
> >>
> >> The LSM ID values are sequential, with the oldest module
> >> LSM_ID_CAPABILITY being the lowest value and the existing modules
> >> numbered in the order they were included in the main line kernel.
> >> This is an arbitrary convention for assigning the values, but
> >> none better presents itself. The value 0 is defined as being invalid.
> >> The values 1-99 are reserved for any special case uses which may
> >> arise in the future.
> >
> > What would be a "special case" that deserves a lower number?
>
> I don't see any meaningful use case for these reserved numbers either.
> If there are some, let's put them now, otherwise we should start with 1.
> Is it inspired by an existing UAPI?
> Reserving 0 as invalid is good though.

I haven't finished reviewing this latest patchset, but I wanted to
comment on this quickly while I had a moment in front of a keyboard
... I did explain my desire and reasoning for this in a previous
revision of this patchset and I still believe the
reserved-for-potential-future-use to be a valid reason so I'm going to
ask for this to remain.  Several of you may disagree, but unless you
can provide a reason why these reserved values would *seriously* break
these, or potential future syscalls, I'm going to be stubborn and
insist we retain a set of low-numbered reserved values.

-- 
paul-moore.com