linux-kernel - Re: [PATCH 0/2] Introduce security_create_user

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Message-ID: <CAHC9VhQQJH95jTWMOGDB4deS=whSfnaF_e73zoabOOeHJMv+0Q@mail.gmail.com>
Date:   Mon, 27 Jun 2022 18:27:41 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Christian Brauner <brauner@...nel.org>,
        Frederick Lawler <fred@...udflare.com>,
        Casey Schaufler <casey@...aufler-ca.com>, kpsingh@...nel.org,
        revest@...omium.org, jackmanb@...omium.org, ast@...nel.org,
        andrii@...nel.org, kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, jmorris@...ei.org, serge@...lyn.com,
        bpf@...r.kernel.org, linux-security-module@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...udflare.com
Subject: Re: [PATCH 0/2] Introduce security_create_user_ns()

On Mon, Jun 27, 2022 at 6:15 PM Daniel Borkmann <daniel@...earbox.net> wrote:
> On 6/27/22 11:56 PM, Paul Moore wrote:
> > On Mon, Jun 27, 2022 at 8:11 AM Christian Brauner <brauner@...nel.org> wrote:
> >> On Thu, Jun 23, 2022 at 11:21:37PM -0400, Paul Moore wrote:
> >
> > ...
> >
> >>> This is one of the reasons why I usually like to see at least one LSM
> >>> implementation to go along with every new/modified hook.  The
> >>> implementation forces you to think about what information is necessary
> >>> to perform a basic access control decision; sometimes it isn't always
> >>> obvious until you have to write the access control :)
> >>
> >> I spoke to Frederick at length during LSS and as I've been given to
> >> understand there's a eBPF program that would immediately use this new
> >> hook. Now I don't want to get into the whole "Is the eBPF LSM hook
> >> infrastructure an LSM" but I think we can let this count as a legitimate
> >> first user of this hook/code.
> >
> > Yes, for the most part I don't really worry about the "is a BPF LSM a
> > LSM?" question, it's generally not important for most discussions.
> > However, there is an issue unique to the BPF LSMs which I think is
> > relevant here: there is no hook implementation code living under
> > security/.  While I talked about a hook implementation being helpful
> > to verify the hook prototype, it is also helpful in providing an
> > in-tree example for other LSMs; unfortunately we don't get that same
> > example value when the initial hook implementation is a BPF LSM.
>
> I would argue that such a patch series must come together with a BPF
> selftest which then i) contains an in-tree usage example, ii) adds BPF
> CI test coverage. Shipping with a BPF selftest at least would be the
> usual expectation.

I'm not going to disagree with that, I generally require matching
tests for new SELinux kernel code, but I was careful to mention code
under 'security/' and not necessarily just a test implementation :)  I
don't want to get into a big discussion about it, but I think having a
working implementation somewhere under 'security/' is more
discoverable for most LSM folks.

-- 
paul-moore.com