Re: [PATCH bpf-next] bpf: allow CGROUP_SKB programs to use bpf_get_current_cgroup_id() helper

[Roman Gushchin <guro@fb.com>]

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!