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Subject: Re: [PATCH bpf-next] bpf: allow CGROUP_SKB programs to use
 bpf_get_current_cgroup_id() helper
To:     Roman Gushchin <guro@fb.com>, Alexei Starovoitov <ast@kernel.org>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>
Cc:     Kernel Team <Kernel-team@fb.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Yonghong Song <yhs@fb.com>
References: <20190606185911.4089151-1-guro@fb.com>
 <20190606190752.GA28743@tower.DHCP.thefacebook.com>
From:   Daniel Borkmann <daniel@iogearbox.net>
Message-ID: <a604b9eb-4e39-c4ec-0868-bac360bc2fb4@iogearbox.net>
Date:   Thu, 6 Jun 2019 21:39:35 +0200
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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?

Thanks,
Daniel