linux-kernel - Re: [PATCH v2 net-next 1/3] bpf: enable non-root eBPF programs

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Message-ID: <5617F9C9.10407@plumgrid.com>
Date:	Fri, 9 Oct 2015 10:30:49 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	"David S. Miller" <davem@...emloft.net>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Kees Cook <keescook@...omium.org>, linux-api@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net-next 1/3] bpf: enable non-root eBPF programs

On 10/9/15 4:45 AM, Hannes Frederic Sowa wrote:
> Afaics this problem hasn't even be solved in
> perf so far, tracepoints hit independent of the namespace currently.

yes and that's exactly what we're trying to solve.
The "demux+worker bpf programs" proposal is a work-in-progress solution
to get confidence how to actually separate tracepoint events into
namespaces before adding any new APIs to kernel.

> For me namespacing of ebpf code is actually not that important, I would
> much rather like to control which namespace is allowed to execute ebpf
> in an unpriviledged manner. Like Thomas wrote, a capability was great
> for that, but I don't know if any new capabilities will be added.

I think we're mixing too many things here.
First I believe eBPF 'socket filters' do not need any caps.
They're packet read-only and functionally very similar to classic with
a distinction that packet data can be aggregated into maps and programs
can be written in C. So I see no reason to restrict them per user or
per namespace.
Openstack use case is different. There it will be prog_type_sched_cls
that can mangle packets, change skb metadata, etc under TC framework.
These are not suitable for all users and this patch leaves
them root-only. If you're proposing to add CAP_BPF_TC to let containers
use them without being CAP_SYS_ADMIN, then I agree, it is useful, but
needs a lot more safety analysis on tc side.
Similar for prog_type_kprobe: we can add CAP_BPF_KPROBE to let
some trusted applications run unprivileged, but still being able
to do performance monitoring/analytics.
And we would need to carefully think about program restrictions,
since bpf_probe_read and kernel pointer walking is essential part
in tracing.

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