linux-kernel - Re: [PATCH bpf-next v7 4/8] bpf: lsm: Implement attach, detach and execution

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Message-ID: <20200327191731.GA9419@chromium.org>
Date:   Fri, 27 Mar 2020 20:17:31 +0100
From:   KP Singh <kpsingh@...omium.org>
To:     Kees Cook <keescook@...omium.org>, James Morris <jmorris@...ei.org>
Cc:     Casey Schaufler <casey@...aufler-ca.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Brendan Jackman <jackmanb@...gle.com>,
        Florent Revest <revest@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Paul Turner <pjt@...gle.com>, Jann Horn <jannh@...gle.com>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Paul Moore <paul@...l-moore.com>
Subject: Re: [PATCH bpf-next v7 4/8] bpf: lsm: Implement attach, detach and
 execution

On 27-Mär 11:59, Kees Cook wrote:
> On Fri, Mar 27, 2020 at 09:36:15AM -0700, Casey Schaufler wrote:
> > On 3/27/2020 6:43 AM, Stephen Smalley wrote:
> > > On 3/27/20 8:41 AM, KP Singh wrote:
> > >> On 27-Mär 08:27, Stephen Smalley wrote:
> > >>>>> +        return -EPERM;

[...]

> > >
> > > I would favor removing the CAP_MAC_ADMIN check here, and implementing it in a bpf_prog hook for Smack and AppArmor if they want that.  SELinux would implement its own check in its existing bpf_prog hook.
> > >
> > The whole notion of one security module calling into another for permission
> > to do something still gives me the heebee jeebees, but if more nimble minds
> > than mine think this is a good idea I won't nack it.
> 
> Well, it's a hook into BPF prog creation, not the BPF LSM specifically,
> so that's why I think it's general enough control without it being
> directly weird. :)
> 
> As far as dropping CAP_MAC_ADMIN, yeah, that should be fine. Creating LSM
> BPF programs already requires CAP_SYS_ADMIN, so for SELinux-less systems,
> that's likely fine. If we need to change the BPF program creation access
> control in the future we can revisit it then.

Sounds good, I will send out v8 carrying James and Andri's
Acks/Review tags, CAP_MAC_ADMIN check removed and some other minor
fixes.

- KP

> 
> -- 
> Kees Cook