Re: [RFC PATCH bpf-next 00/13] bpf: Introduce BPF namespace

[Yafang Shao]

On Sat, Apr 8, 2023 at 12:05 AM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> On Fri, Apr 7, 2023 at 8:59 AM Andrii Nakryiko
> <andrii.nakryiko@xxxxxxxxx> wrote:
> >
> > On Thu, Apr 6, 2023 at 6:44 PM Alexei Starovoitov
> > <alexei.starovoitov@xxxxxxxxx> wrote:
> > >
> > > On Thu, Apr 06, 2023 at 01:22:26PM -0700, Andrii Nakryiko wrote:
> > > > On Wed, Apr 5, 2023 at 10:44 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
> > > > >
> > > > > On Thu, Apr 6, 2023 at 12:24 PM Alexei Starovoitov
> > > > > <alexei.starovoitov@xxxxxxxxx> wrote:
> > > > > >
> > > > > > On Wed, Apr 5, 2023 at 8:22 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
> > > > > > >
> > > > > > > On Thu, Apr 6, 2023 at 11:06 AM Alexei Starovoitov
> > > > > > > <alexei.starovoitov@xxxxxxxxx> wrote:
> > > > > > > >
> > > > > > > > On Wed, Apr 5, 2023 at 7:55 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
> > > > > > > > >
> > > > > > > > > It seems that I didn't describe the issue clearly.
> > > > > > > > > The container doesn't have CAP_SYS_ADMIN, but the CAP_SYS_ADMIN is
> > > > > > > > > required to run bpftool,  so the bpftool running in the container
> > > > > > > > > can't get the ID of bpf objects or convert IDs to FDs.
> > > > > > > > > Is there something that I missed ?
> > > > > > > >
> > > > > > > > Nothing. This is by design. bpftool needs sudo. That's all.
> > > > > > > >
> > > > > > >
> > > > > > > Hmm, what I'm trying to do is make bpftool run without sudo.
> > > > > >
> > > > > > This is not a task that is worth solving.
> > > > > >
> > > > >
> > > > > Then the container with CAP_BPF enabled can't even iterate its bpf progs ...
> > > >
> > > > I'll leave the BPF namespace discussion aside (I agree that it needs
> > > > way more thought).
> > > >
> > > > I am a bit surprised that we require CAP_SYS_ADMIN for GET_NEXT_ID
> > > > operations. GET_FD_BY_ID is definitely CAP_SYS_ADMIN, as they allow
> > > > you to take over someone else's link and stuff like this. But just
> > > > iterating IDs seems like a pretty innocent functionality, so maybe we
> > > > should remove CAP_SYS_ADMIN for GET_NEXT_ID?
> > > >
> > > > By itself GET_NEXT_ID is relatively useless without capabilities, but
> > > > we've been floating the idea of providing GET_INFO_BY_ID (not by FD)
> > > > for a while now, and that seems useful in itself, as it would indeed
> > > > help tools like bpftool to get *some* information even without
> > > > privileges. Whether those GET_INFO_BY_ID operations should return same
> > > > full bpf_{prog,map,link,btf}_info or some trimmed down version of them
> > > > would be up to discussion, but I think getting some info without
> > > > creating an FD seems useful in itself.
> > > >
> > > > Would it be worth discussing and solving this separately from
> > > > namespacing issues?
> > >
> > > Iteration of IDs itself is fine. The set of IDs is not security sensitive,
> > > but GET_NEXT_BY_ID has to be carefully restricted.
> > > It returns xlated, jited, BTF, line info, etc
> > > and with all the restrictions it would need something like
> > > CAP_SYS_PTRACE and CAP_PERFMON to be useful.
> > > And with that we're not far from CAP_SYS_ADMIN.
> > > Why bother then?
> >
> > You probably meant that GET_INFO_BY_ID should be carefully restricted?
>
> yes.
>
> > So yeah, that's what I said that this would have to be discussed
> > further. I agree that returning func/line info, program dump, etc is
> > probably a privileged part. But there is plenty of useful info besides
> > that (e.g., prog name, insns cnt, run stats, etc) that would be useful
> > for unpriv applications to monitor their own apps that they opened
> > from BPF FS, or just some observability daemons.
> >
> > There is a lot of useful information in bpf_map_info and bpf_link_info
> > that's way less privileged. I think bpf_link_info is good as is. Same
> > for bpf_map_info.
> >
> > Either way, I'm not insisting, just something that seems pretty simple
> > to add and useful in some scenarios. We can reuse existing code and
> > types for GET_INFO_BY_FD and just zero-out (or prevent filling out)
> > those privileged fields you mentioned. Anyway, something to put on the
> > backburner, perhaps.
>
> Sorry, but I only see negatives. It's an extra code in the kernel
> that has to be carefully reviewed when initially submitted and
> then every patch that touches get_info_by_id would have to go
> through a microscope every time to avoid introducing a security issue.
> And for what? So that CAP_BPF application can read prog name and run stats?

Per my experience, observability is a very important part for a
project. If the user can't observe the object directly created by it,
he will worry about or even mistrust it.
However I don't insist on it either if you think we shouldn't do it.

-- 
Regards
Yafang