linux-kernel - Re: [PATCH bpf-next] bpf: allow CGROUP_SKB programs to use bpf_get_current_cgroup

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Date:   Thu, 6 Jun 2019 21:59:13 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Roman Gushchin <guro@...com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Yonghong Song <yhs@...com>
Subject: Re: [PATCH bpf-next] bpf: allow CGROUP_SKB programs to use
 bpf_get_current_cgroup_id() helper

On 06/06/2019 09:53 PM, Roman Gushchin wrote:
> On Thu, Jun 06, 2019 at 09:39:35PM +0200, Daniel Borkmann wrote:
>> On 06/06/2019 09:08 PM, Roman Gushchin wrote:
>>> On Thu, Jun 06, 2019 at 11:59:11AM -0700, Roman Gushchin wrote:
>>>> Currently bpf_get_current_cgroup_id() is not supported for
>>>> CGROUP_SKB programs. An attempt to load such a program generates an
>>>> error like this:
>>>>     libbpf:
>>>>     0: (b7) r6 = 0
>>>>     ...
>>>>     8: (63) *(u32 *)(r10 -28) = r6
>>>>     9: (85) call bpf_get_current_cgroup_id#80
>>>>     unknown func bpf_get_current_cgroup_id#80
>>>>
>>>> There are no particular reasons for denying it,
>>>> and we have some use cases where it might be useful.
>>>
>>> Ah, sorry, it's not so simple, as we probably need to take
>>> the cgroup pointer from the socket, not from current.
>>>
>>> So the implementation of the helper should be different
>>> for this type of programs.
>>>
>>> So I wonder if it's better to introduce a new helper
>>> bpf_get_sock_cgroup_id()?
>>>
>>> What do you think?
>>
>> We do have bpf_skb_cgroup_id(), did you give that a try?
> 
> It also isn't supported for CGROUP_SKB, but other than that looks
> exactly what I need.
> 
> Thank you for pointing at it!

Yes, the helper would need to be enabled there.

Cheers,
Daniel