netdev - Re: [PATCH bpf-next v5 3/8] bpf: per-cgroup lsm flavor

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Date:   Wed, 27 Apr 2022 13:17:35 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org
Subject: Re: [PATCH bpf-next v5 3/8] bpf: per-cgroup lsm flavor

On Wed, Apr 27, 2022 at 10:47:48AM -0700, Stanislav Fomichev wrote:
> Regarding cgroup_id+attach_type key of local storage: maybe prohibit
> that mode for BPF_LSM_CGROUP ? We have two modes: (1) keyed by
> cgroup_id+attach_type and (2) keyed by cgroup_id only (and might be
> shared across attach_types). The first one never made much sense to
> me; the second one behaves exactly like the rest of local storages
> (file/sk/etc). WDYT? (we can enable (1) if we ever decide that it's
> needed)
Ah right, cgroup local_storage has already allowed keys in different
granularity and is using key_size to decide which part of
the bpf_cgroup_storage_key should be used.

In that case, may be just allow (1) and (2) now to avoid a new
inconsistent usage surprise with other existing cgroup's prog type.
In the future, if a more granular cgroup local_storage is needed,
the attach_btf_id can be added to 'struct bpf_cgroup_storage_key'.
The existing non BPF_LSM_CGROUP prog will always have attach_btf_id 0.
Would that work?

One caveat though, sizeof(bpf_cgroup_storage_key) is 16 now with
4 bytes padding at the end, so the future __u32 attach_btf_id may
not be able to use the padding in order to get a different size.
I think it is minor and should be ok.