Re: [PATCH ipsec-next] xfrm: interface: support collect metadata mode

[Steffen Klassert <steffen.klassert@secunet.com>]

On Sat, Nov 21, 2020 at 04:28:23PM +0200, 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_IP_TUNNEL
> since the only needed property is the if_id stored in the tun_id member
> of the ip_tunnel_info->key.

Can we please have a separate metadata type for xfrm interfaces?

Sharing such structures turned already out to be a bad idea
on vti interfaces, let's try to avoid that misstake with
xfrm interfaces.

> 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@gmail.com>

The rest of the patch looks good.

Thanks!