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

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Message-ID: <CAADnVQKr5Y3z9f_Vv49DvRFcN+OF3JaFx_9NgBL58pz+TLq8ig@mail.gmail.com>
Date:   Wed, 5 Apr 2023 21:24:00 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     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 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.

> > > Some questions,
> > > - What if the process exits after attaching the bpf prog and the prog
> > > is not auto-detachable?
> > >   For example, the reuserport bpf prog is not auto-detachable. After
> > > pins the reuserport bpf prog, a task can attach it through the pinned
> > > bpf file, but if the task forgets to detach it and the pinned file is
> > > removed, then it seems there's no way to figure out which task or
> > > cgroup this prog belongs to...
> >
> > you're saying that there is a bpf prog in the kernel without
> > corresponding user space ?
>
> No, it is corresponding to user space. For example, it may be
> corresponding to a socket fd, or a cgroup fd.
>
> > Meaning no user space process has an FD
> > that points to this prog or FD to a map that this prog is using?
> > In such a case this is truly kernel bpf prog. It doesn't belong to cgroup.
> >
>
> Even if it is kernel bpf prog, it is created by a process. The user
> needs to know which one created it.

In some situations it's certainly interesting to know which process
loaded a particular program.
In many other situations it's irrelevant.
For example, the process that loaded a prog could have been moved to a
different cgroup.
If you want to track the loading you need to install bpf_lsm
that monitors prog_load hook and collect that info.
It's not the job of the kernel to do it.

> > > - Could you pls. explain in detail how to get comm, pid, or cgroup
> > > from a pinned bpffs file?
> >
> > pinned bpf prog and no user space holds FD to it?
> > It's not part of any cgroup. Nothing to print.
>
> As I explained above, even if it holds nothing, the user needs to know
> the information from it. For example, if it is expected, which one
> created it?

See the answer above. The kernel has enough hooks already to provide
this information to user space. No kernel changes necessary.