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

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Message-ID: <6a8fba0a-c9c9-61ba-793a-c2e0c2924f88@iogearbox.net>
Date:   Tue, 28 Jun 2022 00:15:22 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Paul Moore <paul@...l-moore.com>,
        Christian Brauner <brauner@...nel.org>
Cc:     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 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.

Thanks,
Daniel