netdev - Re: [PATCH ipsec-next 2/3] xfrm: interface: support collect metadata mode

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Date:   Wed, 24 Aug 2022 21:25:37 +0300
From:   Eyal Birger <eyal.birger@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, steffen.klassert@...unet.com,
        herbert@...dor.apana.org.au, pablo@...filter.org,
        contact@...elbtn.com, dsahern@...nel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, devel@...ux-ipsec.org
Subject: Re: [PATCH ipsec-next 2/3] xfrm: interface: support collect metadata mode

Hi Daniel,

On Wed, Aug 24, 2022 at 8:06 PM Daniel Borkmann <daniel@...earbox.net> wrote:
>
> Hi Eyal,
>
> On 8/23/22 5:45 PM, Eyal Birger wrote:
> > This commit adds support for 'collect_md' mode on xfrm interfaces.
> >
> > Each net can have one collect_md device, created by providing the
> > IFLA_XFRM_COLLECT_METADATA flag at creation. This device cannot be
> > altered and has no if_id or link device attributes.
> >
> > On transmit to this device, the if_id is fetched from the attached dst
> > metadata on the skb. The dst metadata type used is METADATA_XFRM
> > which holds the if_id property.
> >
> > On the receive side, xfrmi_rcv_cb() populates a dst metadata for each
> > packet received and attaches it to the skb. The if_id used in this case is
> > fetched from the xfrm state. This can later be used by upper layers such
> > as tc, ebpf, and ip rules.
> >
> > Because the skb is scrubed in xfrmi_rcv_cb(), the attachment of the dst
> > metadata is postponed until after scrubing. Similarly, xfrm_input() is
> > adapted to avoid dropping metadata dsts by only dropping 'valid'
> > (skb_valid_dst(skb) == true) dsts.
> >
> > Policy matching on packets arriving from collect_md xfrmi devices is
> > done by using the xfrm state existing in the skb's sec_path.
> > The xfrm_if_cb.decode_cb() interface implemented by xfrmi_decode_session()
> > is changed to keep the details of the if_id extraction tucked away
> > in xfrm_interface.c.
> >
> > Signed-off-by: Eyal Birger <eyal.birger@...il.com>
>
> Can be done in follow-up (once merged back from net-next into bpf-next),
> but it would be nice to also have a BPF CI selftest for it to make sure
> the ipsec+collect_md with BPF is consistently tested for incoming patches.

Indeed. Note that this requires the addition of set/get bpf helpers for
this metadata as the existing helpers are tied to ip_tunnel_info.

I used such helpers as part of testing this patch series, and plan to submit
them with the respective tests to bpf-next once this feature is merged in
its final form.

Thanks!
Eyal