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

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Message-ID: <CAADnVQJGxR=QT4tVKHbdhRsf5507NWcSmnu7R1H_1dKD7vpzBg@mail.gmail.com>
Date:   Fri, 7 Apr 2023 08:32:49 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Song Liu <song@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH bpf-next 00/13] bpf: Introduce BPF namespace

On Thu, Apr 6, 2023 at 9:34 PM Yafang Shao <laoar.shao@...il.com> wrote:
>
> On Fri, Apr 7, 2023 at 9:44 AM Alexei Starovoitov
> <alexei.starovoitov@...il.com> 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@...il.com> wrote:
> > > >
> > > > On Thu, Apr 6, 2023 at 12:24 PM Alexei Starovoitov
> > > > <alexei.starovoitov@...il.com> wrote:
> > > > >
> > > > > On Wed, Apr 5, 2023 at 8:22 PM Yafang Shao <laoar.shao@...il.com> wrote:
> > > > > >
> > > > > > On Thu, Apr 6, 2023 at 11:06 AM Alexei Starovoitov
> > > > > > <alexei.starovoitov@...il.com> wrote:
> > > > > > >
> > > > > > > On Wed, Apr 5, 2023 at 7:55 PM Yafang Shao <laoar.shao@...il.com> 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?
>
> Not sure if I get your point clearly.  I think the reason we introduce
> CAP_BPF is that we don't want the user to enable CAP_SYS_ADMIN.
> Enabling specific CAPs instead of CAP_SYS_ADMIN should be our
> alignment goal, right?

We want users to switch to CAP_BPF (potentially with CAP_PERFMON)
from full CAP_SYS_ADMIN to reduce attack surface of production workloads.
bpftool is a tool for humans to do introspection and debugging.
It will stay root only.

> If so, then it is worth doing.  As Andrii suggested, a trimmed down
> version is also helpful and should be acceptable.

It's not helpful. It's actively misleading.