linux-kernel - Re: [PATCH security-next v4 23/32] selinux: Remove boot parameter

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Message-ID: <CAGXu5jJtC1gkJ0ZKDFroL8UzvjiPfmC+6EsrzyB0j0oETdSQQg@mail.gmail.com>
Date:   Tue, 2 Oct 2018 12:17:10 -0700
From:   Kees Cook <keescook@...omium.org>
To:     John Johansen <john.johansen@...onical.com>
Cc:     Jordan Glover <Golden_Miller83@...tonmail.ch>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        "Schaufler, Casey" <casey.schaufler@...el.com>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH security-next v4 23/32] selinux: Remove boot parameter

On Tue, Oct 2, 2018 at 11:57 AM, John Johansen
<john.johansen@...onical.com> wrote:
> Under the current scheme
>
> lsm.enabled=selinux
>
> could actually mean selinux,yama,loadpin,something_else are
> enabled. If we extend this behavior to when full stacking lands
>
> lsm.enabled=selinux,yama
>
> might mean selinux,yama,apparmor,loadpin,something_else
>
> and what that list is will vary from kernel to kernel, which I think
> is harder for the user than the lsm.enabled list being what is
> actually enabled at boot

Ah, I think I missed this in your earlier emails. What you don't like
here is that "lsm.enable=" is additive. You want it to be explicit.

Are you okay with lsm.order= having fallback?

The situation we were trying to solve was with new LSMs getting
implicitly disabled if someone is booting with an explicit list. For
example:

lsm.enable=yama,apparmor

means when "landlock" gets added to the kernel, it will be implicitly disabled.

> If we have to have multiple kernel parameter, I prefer a behvior where
> if you hav conflicting kernel parameters specified
>
>   apparmor=0 lsm.enabled=apparmor
>
> that the conflict is logged and the lsm is left disabled, as I think
> it is easier for users to understand than the overrides scheme of v3,
> and sans logging of the conflict is effectively what we had in the
> past
>
>   apparmor=0 security=apparmor
> or
>   apparmor=1 security=selinux
>
> would result in apparmor being disabed

Okay, so for this part you want per-LSM boot param to have priority
(which seems to match SELinux's concerns), possibly logging the
conflict, but still accepting the apparmor= and selinux= state.
security= would still driving initialization ordering (so I think the
behavior I have in the series would be correct).

> That being said I get we have a mess currently, and there really
> doesn't seem to be a good way to fix it. I think getting this right
> for the user is important enough that I am willing to break current
> apparmor userspace api. While apparmor=0 is documented we have also
> documented security=X for years and apparmor=0 isn't used too often
> so I think we can drop it to help clean this mess up abit.
>
> I am not going to Nak, or block on v3 behavior if that is considered
> the best path forward after this discussion/rant.

I could define CONFIG_LSM_ENABLE as being "additive" to
SECURITY_APPARMOR_BOOTPARAM_VALUE and
SECURITY_SELINUX_BOOTPARAM_VALUE?

-Kees

-- 
Kees Cook
Pixel Security