netdev - Re: [PATCH v2 bpf-next 2/3] bpf: implement CAP

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Message-ID: <46df2c36-4276-33c0-626b-c51e77b3a04f@fb.com>
Date:   Wed, 4 Sep 2019 01:39:28 +0000
From:   Alexei Starovoitov <ast@...com>
To:     "nicolas.dichtel@...nd.com" <nicolas.dichtel@...nd.com>,
        "Alexei Starovoitov" <alexei.starovoitov@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>
CC:     Alexei Starovoitov <ast@...nel.org>,
        "luto@...capital.net" <luto@...capital.net>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next 2/3] bpf: implement CAP_BPF

On 8/30/19 8:19 AM, Nicolas Dichtel wrote:
> Le 29/08/2019 à 19:30, Alexei Starovoitov a écrit :
> [snip]
>> These are the links that showing that k8 can delegates caps.
>> Are you saying that you know of folks who specifically
>> delegate cap_sys_admin and cap_net_admin _only_ to a container to run bpf in there?
>>
> Yes, we need cap_sys_admin only to load bpf:
> tc filter add dev eth0 ingress matchall action bpf obj ./tc_test_kern.o sec test
> 
> I'm not sure to understand why cap_net_admin is not enough to run the previous
> command (ie why load is forbidden).

because bpf syscall prog_load command requires cap_sys_admin in
the current implementation.

> I want to avoid sys_admin, thus cap_bpf will be ok. But we need to manage the
> backward compatibility.

re: backward compatibility...
do you know of any case where task is running under userid=nobody
with cap_sys_admin and cap_net_admin in order to do bpf ?

If not then what is the concern about compatibility?