[net-next v2 1/1] net: seg6: Add support for SRv6 Headend Reduced Encapsulation

[Anton Makarov <antonmakarov11235@gmail.com>]

SRv6 Headend H.Encaps.Red and H.Encaps.L2.Red behaviors are implemented
accordingly to RFC 8986. The H.Encaps.Red is an optimization of
The H.Encaps behavior. The H.Encaps.L2.Red is an optimization of
the H.Encaps.L2 behavior. Both new behaviors reduce the length of
the SRH by excluding the first SID in the SRH of the pushed IPv6 header.
The first SID is only placed in the Destination Address field
of the pushed IPv6 header.

The push of the SRH is omitted when the SRv6 Policy only contains
one segment.

Signed-off-by: Anton Makarov <anton.makarov11235@gmail.com>
---
v2: 1) Fixed sparse warnings
    2) memset now uses sizeof() instead of hardcoded value
    3) Removed EXPORT_SYMBOL_GPL
---
 include/net/seg6.h                 |  2 +
 include/uapi/linux/seg6_iptunnel.h |  2 +
 net/ipv6/seg6_iptunnel.c           | 94 +++++++++++++++++++++++++++++-
 3 files changed, 96 insertions(+), 2 deletions(-)

diff --git a/include/net/seg6.h b/include/net/seg6.h
index af668f17b398..8d0ce782f830 100644
--- a/include/net/seg6.h
+++ b/include/net/seg6.h
@@ -62,6 +62,8 @@ extern struct ipv6_sr_hdr *seg6_get_srh(struct sk_buff *skb, int flags);
 extern void seg6_icmp_srh(struct sk_buff *skb, struct inet6_skb_parm *opt);
 extern int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh,
 			     int proto);
+extern int seg6_do_srh_encap_red(struct sk_buff *skb, struct ipv6_sr_hdr *osrh,
+			     int proto);
 extern int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh);
 extern int seg6_lookup_nexthop(struct sk_buff *skb, struct in6_addr *nhaddr,
 			       u32 tbl_id);
diff --git a/include/uapi/linux/seg6_iptunnel.h b/include/uapi/linux/seg6_iptunnel.h
index eb815e0d0ac3..a9fa777f16de 100644
--- a/include/uapi/linux/seg6_iptunnel.h
+++ b/include/uapi/linux/seg6_iptunnel.h
@@ -35,6 +35,8 @@ enum {
 	SEG6_IPTUN_MODE_INLINE,
 	SEG6_IPTUN_MODE_ENCAP,
 	SEG6_IPTUN_MODE_L2ENCAP,
+	SEG6_IPTUN_MODE_ENCAP_RED,
+	SEG6_IPTUN_MODE_L2ENCAP_RED,
 };
 
 #endif
diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c
index d64855010948..e70c0401715e 100644
--- a/net/ipv6/seg6_iptunnel.c
+++ b/net/ipv6/seg6_iptunnel.c
@@ -36,9 +36,11 @@ static size_t seg6_lwt_headroom(struct seg6_iptunnel_encap *tuninfo)
 	case SEG6_IPTUN_MODE_INLINE:
 		break;
 	case SEG6_IPTUN_MODE_ENCAP:
+	case SEG6_IPTUN_MODE_ENCAP_RED:
 		head = sizeof(struct ipv6hdr);
 		break;
 	case SEG6_IPTUN_MODE_L2ENCAP:
+	case SEG6_IPTUN_MODE_L2ENCAP_RED:
 		return 0;
 	}
 
@@ -195,6 +197,80 @@ int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
 }
 EXPORT_SYMBOL_GPL(seg6_do_srh_encap);
 
+/* encapsulate an IPv6 packet within an outer IPv6 header with reduced SRH */
+int seg6_do_srh_encap_red(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
+{
+	struct dst_entry *dst = skb_dst(skb);
+	struct net *net = dev_net(dst->dev);
+	struct ipv6hdr *hdr, *inner_hdr6;
+	struct iphdr *inner_hdr4;
+	struct ipv6_sr_hdr *isrh;
+	int hdrlen = 0, tot_len, err;
+	__be32 flowlabel = 0;
+
+	if (osrh->first_segment > 0)
+		hdrlen = (osrh->hdrlen - 1) << 3;
+
+	tot_len = hdrlen + sizeof(struct ipv6hdr);
+
+	err = skb_cow_head(skb, tot_len + skb->mac_len);
+	if (unlikely(err))
+		return err;
+
+	inner_hdr6 = ipv6_hdr(skb);
+	inner_hdr4 = ip_hdr(skb);
+	flowlabel = seg6_make_flowlabel(net, skb, inner_hdr6);
+
+	skb_push(skb, tot_len);
+	skb_reset_network_header(skb);
+	skb_mac_header_rebuild(skb);
+	hdr = ipv6_hdr(skb);
+
+	memset(skb->cb, 0, sizeof(skb->cb));
+	IP6CB(skb)->iif = skb->skb_iif;
+
+	if (skb->protocol == htons(ETH_P_IPV6)) {
+		ip6_flow_hdr(hdr, ip6_tclass(ip6_flowinfo(inner_hdr6)),
+			     flowlabel);
+		hdr->hop_limit = inner_hdr6->hop_limit;
+	} else if (skb->protocol == htons(ETH_P_IP)) {
+		ip6_flow_hdr(hdr, (unsigned int) inner_hdr4->tos, flowlabel);
+		hdr->hop_limit = inner_hdr4->ttl;
+	}
+
+	skb->protocol = htons(ETH_P_IPV6);
+
+	hdr->daddr = osrh->segments[osrh->first_segment];
+	hdr->version = 6;
+
+	if (osrh->first_segment > 0) {
+		hdr->nexthdr = NEXTHDR_ROUTING;
+
+		isrh = (void *)hdr + sizeof(struct ipv6hdr);
+		memcpy(isrh, osrh, hdrlen);
+
+		isrh->nexthdr = proto;
+		isrh->first_segment--;
+		isrh->hdrlen -= 2;
+	} else {
+		hdr->nexthdr = proto;
+	}
+
+	set_tun_src(net, dst->dev, &hdr->daddr, &hdr->saddr);
+
+#ifdef CONFIG_IPV6_SEG6_HMAC
+	if (osrh->first_segment > 0 && sr_has_hmac(isrh)) {
+		err = seg6_push_hmac(net, &hdr->saddr, isrh);
+		if (unlikely(err))
+			return err;
+	}
+#endif
+
+	skb_postpush_rcsum(skb, hdr, tot_len);
+
+	return 0;
+}
+
 /* insert an SRH within an IPv6 packet, just after the IPv6 header */
 int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh)
 {
@@ -265,6 +341,7 @@ static int seg6_do_srh(struct sk_buff *skb)
 			return err;
 		break;
 	case SEG6_IPTUN_MODE_ENCAP:
+	case SEG6_IPTUN_MODE_ENCAP_RED:
 		err = iptunnel_handle_offloads(skb, SKB_GSO_IPXIP6);
 		if (err)
 			return err;
@@ -276,7 +353,11 @@ static int seg6_do_srh(struct sk_buff *skb)
 		else
 			return -EINVAL;
 
-		err = seg6_do_srh_encap(skb, tinfo->srh, proto);
+		if (tinfo->mode == SEG6_IPTUN_MODE_ENCAP)
+			err = seg6_do_srh_encap(skb, tinfo->srh, proto);
+		else
+			err = seg6_do_srh_encap_red(skb, tinfo->srh, proto);
+
 		if (err)
 			return err;
 
@@ -285,6 +366,7 @@ static int seg6_do_srh(struct sk_buff *skb)
 		skb->protocol = htons(ETH_P_IPV6);
 		break;
 	case SEG6_IPTUN_MODE_L2ENCAP:
+	case SEG6_IPTUN_MODE_L2ENCAP_RED:
 		if (!skb_mac_header_was_set(skb))
 			return -EINVAL;
 
@@ -294,7 +376,11 @@ static int seg6_do_srh(struct sk_buff *skb)
 		skb_mac_header_rebuild(skb);
 		skb_push(skb, skb->mac_len);
 
-		err = seg6_do_srh_encap(skb, tinfo->srh, IPPROTO_ETHERNET);
+		if (tinfo->mode == SEG6_IPTUN_MODE_L2ENCAP)
+			err = seg6_do_srh_encap(skb, tinfo->srh, IPPROTO_ETHERNET);
+		else
+			err = seg6_do_srh_encap_red(skb, tinfo->srh, IPPROTO_ETHERNET);
+
 		if (err)
 			return err;
 
@@ -514,6 +600,10 @@ static int seg6_build_state(struct net *net, struct nlattr *nla,
 		break;
 	case SEG6_IPTUN_MODE_L2ENCAP:
 		break;
+	case SEG6_IPTUN_MODE_ENCAP_RED:
+		break;
+	case SEG6_IPTUN_MODE_L2ENCAP_RED:
+		break;
 	default:
 		return -EINVAL;
 	}
-- 
2.20.1