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Date: Tue, 28 Jun 2022 10:14:29 -0500 From: Frederick Lawler <fred@...udflare.com> To: Casey Schaufler <casey@...aufler-ca.com>, Paul Moore <paul@...l-moore.com>, Daniel Borkmann <daniel@...earbox.net> Cc: Christian Brauner <brauner@...nel.org>, 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 6:18 PM, Casey Schaufler wrote: > On 6/27/2022 3:27 PM, Paul Moore wrote: >> 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. > > I agree. It would be unfortunate if we added a hook explicitly for eBPF > only to discover that the proposed user needs something different. The > LSM community should have a chance to review the code before committing > to all the maintenance required in supporting it. > > Is there a reference on how to write an eBPF security module? There's a documentation page that briefly touches on a BPF LSM implementation [1]. > There should be something out there warning the eBPF programmer of the > implications of providing a secid_to_secctx hook for starters. > Links: 1. https://docs.kernel.org/bpf/prog_lsm.html?highlight=bpf+lsm#
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