netdev - [patch RFC net-next v2 3/3] udp6: Use Segment Routing Header for dest address if present

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Date:   Wed,  1 Dec 2021 21:25:19 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     unlisted-recipients:; (no To-header on input)
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        James Prestwood <prestwoj@...il.com>,
        Justin Iurman <justin.iurman@...ege.be>,
        Praveen Chaudhary <praveen5582@...il.com>,
        "Jason A . Donenfeld" <Jason@...c4.com>,
        Eric Dumazet <edumazet@...gle.com>,
        netdev <netdev@...r.kernel.org>, Andrew Lunn <andrew@...n.ch>
Subject: [patch RFC net-next v2 3/3] udp6: Use Segment Routing Header for dest address if present

When finding the socket to report an error on, if the invoking packet
is using Segment Routing, the IPv6 destination address is that of an
intermediate router, not the end destination. Extract the ultimate
destination address from the segment address.

This change allows traceroute to function in the presence of Segment
Routing.

Signed-off-by: Andrew Lunn <andrew@...n.ch>
---
 net/ipv6/udp.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 6a0e569f0bb8..6a2288e7ddda 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -40,6 +40,7 @@
 #include <net/transp_v6.h>
 #include <net/ip6_route.h>
 #include <net/raw.h>
+#include <net/seg6.h>
 #include <net/tcp_states.h>
 #include <net/ip6_checksum.h>
 #include <net/ip6_tunnel.h>
@@ -563,12 +564,18 @@ int __udp6_lib_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 	const struct in6_addr *saddr = &hdr->saddr;
 	const struct in6_addr *daddr = &hdr->daddr;
 	struct udphdr *uh = (struct udphdr *)(skb->data+offset);
+	struct ipv6_sr_hdr *srh;
 	bool tunnel = false;
 	struct sock *sk;
 	int harderr;
 	int err;
 	struct net *net = dev_net(skb->dev);
 
+	if (opt->flags & IP6SKB_SEG6) {
+		srh = (struct ipv6_sr_hdr *)(skb->data + opt->srhoff);
+		daddr = &srh->segments[0];
+	}
+
 	sk = __udp6_lib_lookup(net, daddr, uh->dest, saddr, uh->source,
 			       inet6_iif(skb), inet6_sdif(skb), udptable, NULL);
 
-- 
2.33.1