linux-kernel - Re: [PATCH bpf-next v4 3/7] bpf: Introduce BPF_MODIFY

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Message-ID: <2a46d961-5cb8-bfc1-9e42-26d8af97ae86@schaufler-ca.com>
Date:   Thu, 5 Mar 2020 10:47:10 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Stephen Smalley <stephen.smalley.work@...il.com>
Cc:     KP Singh <kpsingh@...omium.org>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        Andrii Nakryiko <andriin@...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>, jmorris@...ei.org,
        Paul Moore <paul@...l-moore.com>
Subject: Re: [PATCH bpf-next v4 3/7] bpf: Introduce BPF_MODIFY_RETURN

On 3/5/2020 10:03 AM, Stephen Smalley wrote:
> On Thu, Mar 5, 2020 at 12:35 PM Casey Schaufler <casey@...aufler-ca.com> wrote:
>> I believe that I have stated that order isn't my issue.
>> Go first, last or as specified in the lsm list, I really
>> don't care. We'll talk about what does matter in the KRSI
>> thread.
> Order matters when the security module logic (in this case, the BPF
> program) is loaded from userspace and
> the userspace process isn't already required to be fully privileged
> with respect to the in-kernel security modules.
> CAP_MAC_ADMIN was their (not unreasonable) attempt to check that
> requirement; it just doesn't happen to convey
> the same meaning for SELinux since SELinux predates the introduction
> of CAP_MAC_ADMIN (in Linux at least) and
> since SELinux was designed to confine even processes with capabilities.

If KRSI "needs" to go last, I'm fine with that. What I continue
to object to is making KRSI/BPF a special case in the code. It
doesn't need to be.