Re: [PATCH v2 bpf-next 00/18] BPF token

Maryam Tahhan
2023-06-22T08:23:03Z

On 22/06/2023 00:48, Andrii Nakryiko wrote:
>
>>>> Giving a way to enable BPF in a container is only a small part of the overall task -- making BPF behave sensibly in that container seems like it should also be necessary.
>>> BPF is still a privileged thing. You can't just say that any
>>> unprivileged application should be able to use BPF. That's why BPF
>>> token is about trusting unpriv application in a controlled environment
>>> (production) to not do something crazy. It can be enforced further
>>> through LSM usage, but in a lot of cases, when dealing with internal
>>> production applications it's enough to have a proper application
>>> design and rely on code review process to avoid any negative effects.
>> We really shouldn’t be creating new kinds of privileged containers that do uncontained things.
>>
>> If you actually want to go this route, I think you would do much better to introduce a way for a container manager to usefully proxy BPF on behalf of the container.
> Please see Hao's reply ([0]) about his and Google's (not so rosy)
> experiences with building and using such BPF proxy. We (Meta)
> internally didn't go this route at all and strongly prefer not to.
> There are lots of downsides and complications to having a BPF proxy.
> In the end, this is just shuffling around where the decision about
> trusting a given application with BPF access is being made. BPF proxy
> adds lots of unnecessary logistical, operational, and development
> complexity, but doesn't magically make anything safer.
>
> [0] https://lore.kernel.org/bpf/CA+khW7h95RpurRL8qmKdSJQEXNYuqSWnP16o-uRZ9G0KqCfM4Q@mail.gmail.com/
>
Apologies for being blunt, but  the token approach to me seems to be a
work around providing the right level/classification for a pod/container
in order to say you support unprivileged containers using eBPF. I think
if your container needs to do privileged things it should have and be
classified with the right permissions (privileges) to do what it needs
to do.

The  proxy BPF on behalf of the container approach works for containers
that don't need to do privileged BPF operations.

I have to say that  the `proxy BPF on behalf of the container` meets the
needs of unprivileged pods and at the same time giving CAP_BPF to the
applications meets the needs of these PODs that need to do
privileged/bpf things without any tokens. Ultimately you are trusting
these apps in the same way as if you were granting a token.

>>> So privileged daemon (container manager) will be configured with the
>>> knowledge of which services/containers are allowed to use BPF, and
>>> will grant BPF token only to those that were explicitly allowlisted.