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

Andrii Nakryiko
2023-06-09T19:08:59Z

On Fri, Jun 9, 2023 at 11:32 AM Andy Lutomirski <luto@kernel.org> wrote:
>
> On Wed, Jun 7, 2023, at 4:53 PM, Andrii Nakryiko wrote:
> > This patch set introduces new BPF object, BPF token, which allows to delegate
> > a subset of BPF functionality from privileged system-wide daemon (e.g.,
> > systemd or any other container manager) to a *trusted* unprivileged
> > application. Trust is the key here. This functionality is not about allowing
> > unconditional unprivileged BPF usage. Establishing trust, though, is
> > completely up to the discretion of respective privileged application that
> > would create a BPF token.
> >
>
> I skimmed the description and the LSFMM slides.
>
> Years ago, I sent out a patch set to start down the path of making the bpf() API make sense when used in less-privileged contexts (regarding access control of BPF objects and such). It went nowhere.
>
> Where does BPF token fit in? Does a kernel with these patches applied actually behave sensibly if you pass a BPF token into a container?

Yes?.. In the sense that it is possible to create BPF programs and BPF
maps from inside the container (with BPF token). Right now under user
namespace it's impossible no matter what you do.

> 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.

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.