netdev - Re: [PATCH ipsec-next,v2 2/3] xfrm: interface: support collect metadata mode

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Date:   Thu, 25 Aug 2022 16:28:51 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Eyal Birger <eyal.birger@...il.com>, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        steffen.klassert@...unet.com, herbert@...dor.apana.org.au,
        dsahern@...nel.org, contact@...elbtn.com, pablo@...filter.org
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH ipsec-next,v2 2/3] xfrm: interface: support collect
 metadata mode


Le 25/08/2022 à 15:46, Eyal Birger a écrit :
> 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. If exists, the link property is also fetched from
> the metadata. The dst metadata type used is METADATA_XFRM which holds
> these properties.
> 
> 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, and the link is fetched from the incoming
> device. This information 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>
> 
> ----
> 
> v2:
>   - add "link" property as suggested by Nicolas Dichtel
Thanks.

[snip]

> @@ -269,10 +303,24 @@ xfrmi_xmit2(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
>  	struct net_device *tdev;
>  	struct xfrm_state *x;
>  	int err = -1;
> +	u32 if_id;
>  	int mtu;
>  
> +	if (xi->p.collect_md) {
> +		struct xfrm_md_info *md_info = skb_xfrm_md_info(skb);
> +
> +		if (unlikely(!md_info))
> +			return -EINVAL;
> +
> +		if_id = md_info->if_id;
> +		if (md_info->link)
> +			fl->flowi_oif = md_info->link;
nit: flowi_oif is 0 in case of collect_md, thus the if can be omitted.

[snip]
> @@ -682,12 +746,19 @@ static int xfrmi_changelink(struct net_device *dev, struct nlattr *tb[],

>  		return -EINVAL;
>  	}
>  
> +	if (p.collect_md) {
> +		NL_SET_ERR_MSG(extack, "collect_md can't be changed");
> +		return -EINVAL;
> +	}
> +
>  	xi = xfrmi_locate(net, &p);
>  	if (!xi) {
>  		xi = netdev_priv(dev);
>  	} else {
>  		if (xi->dev != dev)
>  			return -EEXIST;
> +		if (xi->p.collect_md)
> +			return -EINVAL;

It could be useful to add an extack error msg in this case also.

Regards,
Nicolas