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

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Message-ID: <CAADnVQJ6LSxZ3=x9AnqiYObYaSnKQj1mWB0CzSn2c4PGRmSUSw@mail.gmail.com>
Date:   Fri, 7 Apr 2023 09:05:25 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Yafang Shao <laoar.shao@...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 Fri, Apr 7, 2023 at 8:59 AM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Thu, Apr 6, 2023 at 6:44 PM 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?
>
> 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?