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

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Message-ID: <CAHC9VhQONd9zFJswcAsY9-xQcRhoYwXtwyo4zT5XsSPTEtvuRg@mail.gmail.com>
Date:   Wed, 9 Nov 2022 18:33:46 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     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, mic@...ikod.net
Subject: Re: [PATCH v1 2/8] LSM: Add an LSM identifier for external use

On Tue, Oct 25, 2022 at 2:45 PM Casey Schaufler <casey@...aufler-ca.com> wrote:
>
> Add an integer member "id" to the struct lsm_id. This value is
> a unique identifier associated with each security module. The
> values are defined in a new UAPI header file. 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. The first 32 values (0 - 31) are reserved
> for some as yet unknown but important use.
>
> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> ---
>  include/linux/lsm_hooks.h    |  1 +
>  include/uapi/linux/lsm.h     | 32 ++++++++++++++++++++++++++++++++
>  security/apparmor/lsm.c      |  2 ++
>  security/bpf/hooks.c         |  2 ++
>  security/commoncap.c         |  2 ++
>  security/landlock/setup.c    |  2 ++
>  security/loadpin/loadpin.c   |  2 ++
>  security/lockdown/lockdown.c |  2 ++
>  security/safesetid/lsm.c     |  2 ++
>  security/selinux/hooks.c     |  2 ++
>  security/smack/smack_lsm.c   |  2 ++
>  security/tomoyo/tomoyo.c     |  2 ++
>  security/yama/yama_lsm.c     |  2 ++
>  13 files changed, 55 insertions(+)
>  create mode 100644 include/uapi/linux/lsm.h

Unless you're getting paid by the patch, I'd rather you combine
patches 1/8 and 2/8 into a single patch.  They are both pretty small,
very related, and I don't want to see 1/8 merged anywhere without 2/8.

> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index e383e468f742..dd4b4d95a172 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1607,6 +1607,7 @@ struct security_hook_heads {
>   */
>  struct lsm_id {
>         const char      *lsm;           /* Name of the LSM */
> +       int             id;             /* LSM ID */
>  };

At the very least let's define lsm_id::id as an 'unsigned int' type,
but since we are going to see the lsm_id::id token used as part of the
kernel ABI (likely not in this struct) I agree with Greg's comments
about making the size more explicit.  I would suggest __u32/u32 as
32-bits should be plenty for this token.

Given the other upstream discussions we may want to do something
similar with lsm_id::lsm and __u8/u8.  I'm pretty sure I saw a similar
comment (by Greg?) elsewhere in this patchset when I was quickly
skimming these on my phone while away ...

--
paul-moore.com