netdev - Re: [RFC PATCH bpf-next 0/2] unprivileged BPF_PROG_TEST

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Date:   Thu, 19 Dec 2019 13:52:02 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Edwin Peer <epeer@...iper.net>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Y Song <ys114321@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [RFC PATCH bpf-next 0/2] unprivileged BPF_PROG_TEST_RUN

On Thu, Dec 19, 2019 at 08:06:21PM +0000, Edwin Peer wrote:
> On 12/19/19, 11:26, "Alexei Starovoitov" <alexei.starovoitov@...il.com> wrote:
> 
> > On Thu, Dec 19, 2019 at 05:05:42PM +0000, Edwin Peer wrote:
> >> On 12/19/19, 07:47, "Daniel Borkmann" <daniel@...earbox.net> wrote:
> >> 
> >> >  What about CAP_BPF?
> >> 
> >> What is the status of this? It might solve some of the problems, but it is still puts testing
> >> BPF outside reach of normal users.
> >    
> > why?
> > I think CAP_BPF is solving exactly what you're trying to achieve.
> 
> I'm trying to provide access to BPF testing infrastructure for unprivileged
> users (assuming it can be done in a safe way, which I'm as yet unsure of).
> CAP_BPF is not the same thing, because at least some kind of root
> intervention is required to attain CAP_BPF in the first place.

yes and test infra can bet setup with CAP_BPF.
The desire of testing frameworks to work without root was one of the main
motivations for us to work on CAP_BPF.

> > Whether bpf_clone_redirect() is such helper is still tbd. Unpriv user can flood netdevs
> > without any bpf.
>    
> True, but presumably such would still be subject to administrator
> controlled QoS and firewall policy? Also unprivileged users presumably
> can't create arbitrary packets coming from spoofed IPs / MACs, which I
> believe requires CAP_NET_RAW?
>  
> >> Are there other helpers of concern that come immediately to mind? A first stab might
> >> add these to the list in the verifier that require privilege. This has the drawback that
> >> programs that actually need this kind of functionality are beyond the test framework.
> >    
> >   So far majority of programs require root-only verifier features. The programs are
> >   getting more complex and benefit the most from testing. Relaxing test_run for unpriv
> >   progs is imo very narrow use case. I'd rather use CAP_BPF.
>     
> The more elaborate proposal called for mocking these aspects for
> testing, which could conceivably resolve this? That said, I see an
> incremental path to this, adding such as needed. The narrowness
> of the use case really depends on exactly what you're trying to do.
> Something in XDP, for example, has very little kernel dependencies
> (possibly none that would be affected here) and represents an entire
> class of use cases that could have unprivileged testing be supported.

I'm looking at public and non-public XDP progs and none of them are verifiable
as unpriv. I don't think it's a good idea to build infra for toy programs.