Re: [PATCH bpf-next v6 6/6] bpf: Allow the new syncookie helpers to work with SKBs

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Fri, Apr 22, 2022 at 10:25 AM Maxim Mikityanskiy <maximmi@nvidia.com> wrote:
>
> This commits allows the new BPF helpers to work in SKB context (in TC
> BPF programs): bpf_tcp_raw_{gen,check}_syncookie_ipv{4,6}.
>
> The sample application and selftest are updated to support the TC mode.
> It's not the recommended mode of operation, because the SKB is already
> created at this point, and it's unlikely that the BPF program will
> provide any substantional speedup compared to regular SYN cookies or
> synproxy.
>
> Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
> Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
> ---
>  net/core/filter.c                             |  10 ++
>  .../selftests/bpf/prog_tests/xdp_synproxy.c   |  53 +++++--
>  .../selftests/bpf/progs/xdp_synproxy_kern.c   | 141 +++++++++++++-----
>  tools/testing/selftests/bpf/xdp_synproxy.c    |  94 +++++++++---
>  4 files changed, 230 insertions(+), 68 deletions(-)
>

[...]

>
> -       return hdr.tcp->syn ? syncookie_handle_syn(&hdr, ctx, data, data_end) :
> -                             syncookie_handle_ack(&hdr);
> +       return hdr->tcp->syn ? syncookie_handle_syn(hdr, ctx, data, data_end, xdp) :
> +                              syncookie_handle_ack(hdr);
> +}
> +
> +SEC("xdp/syncookie")

SEC("xdp")? libbpf will reject SEC("xdp/syncookie") in strict libbpf 1.0 mode

> +int syncookie_xdp(struct xdp_md *ctx)
> +{
> +       void *data_end = (void *)(long)ctx->data_end;
> +       void *data = (void *)(long)ctx->data;
> +       struct header_pointers hdr;
> +       int ret;
> +
> +       ret = syncookie_part1(ctx, data, data_end, &hdr, true);
> +       if (ret != XDP_TX)
> +               return ret;
> +
> +       data_end = (void *)(long)ctx->data_end;
> +       data = (void *)(long)ctx->data;
> +
> +       return syncookie_part2(ctx, data, data_end, &hdr, true);
> +}

[...]