netdev - Re: Permissions for eBPF objects

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Date:   Fri, 25 Aug 2017 15:26:39 -0400
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     Jeffrey Vander Stoep <jeffv@...gle.com>,
        Chenbo Feng <fengc@...gle.com>, netdev@...r.kernel.org,
        SELinux <Selinux@...ho.nsa.gov>
Subject: Re: Permissions for eBPF objects

On Fri, 2017-08-25 at 11:01 -0700, Jeffrey Vander Stoep via Selinux
wrote:
> I’d like to get your thoughts on adding LSM permission checks on BPF
> objects.
> 
> By default, the ability to create and use eBPF maps/programs requires
> CAP_SYS_ADMIN [1]. Alternatively, all processes can be granted access
> to bpf() functions. This seems like poor granularity. [2]
> 
> Like files and sockets, eBPF maps and programs can be passed between
> processes by FD and have a number of functions that map cleanly to
> permissions.
> 
> Let me know what you think. Are there simpler alternative approaches
> that we haven’t considered?

Is it possible to create the map/program in one process (with
CAP_SYS_ADMIN), pass the resulting fd to netd, and then use it there
(without requiring CAP_SYS_ADMIN in netd itself)?

What level of granularity would be useful?  Would it go beyond just
being able to use bpf() at all?

> 
> Thanks!
> Jeff
> 
> [1] http://man7.org/linux/man-pages/man2/bpf.2.html NOTES section
> [2] We are considering eBPF for network filtering by netd. Giving
> netd
> CAP_SYS_ADMIN would considerably increase netd’s privileges.
> Alternatively allowing all processes permission to use bpf() goes
> against the principle of least privilege exposing a lot of kernel
> attack surface to processes that do not actually need it.
>