Messages in this thread | | | Date | Tue, 28 Jun 2022 11:44:47 -0500 | Subject | Re: [PATCH 0/2] Introduce security_create_user_ns() | From | Frederick Lawler <> |
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On 6/28/22 11:12 AM, KP Singh wrote: > On Tue, Jun 28, 2022 at 6:02 PM Casey Schaufler <casey@schaufler-ca.com> wrote: >> >> On 6/28/2022 8:14 AM, Frederick Lawler wrote: >>> 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@iogearbox.net> wrote: >>>>>> On 6/27/22 11:56 PM, Paul Moore wrote: >>>>>>> On Mon, Jun 27, 2022 at 8:11 AM Christian Brauner <brauner@kernel.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]. >> >> That's a brief touch, alright. I'll grant that the LSM interface isn't >> especially well documented for C developers, but we have done tutorials >> and have multiple examples. I worry that without an in-tree example for >> eBPF we might well be setting developers up for spectacular failure. >> > > Casey, Daniel and I are recommending an in-tree example, it will be > in BPF selftests and we will CC you on the reviews. > > Frederick, is that okay with you?
Yep.
> >>> >>>> 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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