netdev - Re: [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf

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Date:   Fri, 16 Aug 2019 11:33:57 +0000
From:   Jordan Glover <Golden_Miller83@...tonmail.ch>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Daniel Colascione <dancol@...gle.com>,
        Song Liu <songliubraving@...com>,
        Kees Cook <keescook@...omium.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        Lorenz Bauer <lmb@...udflare.com>,
        Jann Horn <jannh@...gle.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux API <linux-api@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf

On Friday, August 16, 2019 9:59 AM, Thomas Gleixner <tglx@...utronix.de> wrote:

> On Fri, 16 Aug 2019, Jordan Glover wrote:
>
> > "systemd --user" service? Trying to do so will fail with:
> > "Failed to apply ambient capabilities (before UID change): Operation not permitted"
> > I think it's crucial to clear that point to avoid confusion in this discussion
> > where people are talking about different things.
> > On the other hand running "systemd --system" service with:
> > User=nobody
> > AmbientCapabilities=CAP_NET_ADMIN
> > is perfectly legit and clears some security concerns as only privileged user
> > can start such service.
>
> While we are at it, can we please stop looking at this from a systemd only
> perspective. There is a world outside of systemd.
>
> Thanks,
>
> tglx

If you define:

"systemd --user" == unprivileged process started by unprivileged user
"systemd --system" == process started by privileged user but run as another
user which keeps some of parent user privileges and drops others

you can get rid of "systemd" from the equation.

"systemd --user" was the example provided by Alexei when asked about the usecase
but his description didn't match what it does so it's not obvious what the real
usecase is. I'm sure there can be many more examples and systemd isn't important
here in particular beside to understand this specific example.

Jordan