Merge branch 'seg6-allow-end-x-behavior-to-accept-an-oif'

Ido Schimmel says:

====================
seg6: Allow End.X behavior to accept an oif

Patches #1-#3 gradually extend the End.X behavior to accept an output
interface as an optional argument. This is needed for cases where user
space wishes to specify an IPv6 link-local address as the nexthop
address.

Patch #4 adds test cases to the existing End.X selftest to cover the new
functionality.
====================

Link: https://patch.msgid.link/20250612122323.584113-1-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

net/ipv6/seg6_local.c

@@ -270,7 +270,7 @@ static void advance_nextseg(struct ipv6_sr_hdr *srh, struct in6_addr *daddr)
 
 static int
 seg6_lookup_any_nexthop(struct sk_buff *skb, struct in6_addr *nhaddr,
-			u32 tbl_id, bool local_delivery)
+			u32 tbl_id, bool local_delivery, int oif)
 {
 	struct net *net = dev_net(skb->dev);
 	struct ipv6hdr *hdr = ipv6_hdr(skb);
@@ -282,6 +282,7 @@ seg6_lookup_any_nexthop(struct sk_buff *skb, struct in6_addr *nhaddr,
 
 	memset(&fl6, 0, sizeof(fl6));
 	fl6.flowi6_iif = skb->dev->ifindex;
+	fl6.flowi6_oif = oif;
 	fl6.daddr = nhaddr ? *nhaddr : hdr->daddr;
 	fl6.saddr = hdr->saddr;
 	fl6.flowlabel = ip6_flowinfo(hdr);
@@ -291,17 +292,19 @@ seg6_lookup_any_nexthop(struct sk_buff *skb, struct in6_addr *nhaddr,
 	if (nhaddr)
 		fl6.flowi6_flags = FLOWI_FLAG_KNOWN_NH;
 
-	if (!tbl_id) {
+	if (!tbl_id && !oif) {
 		dst = ip6_route_input_lookup(net, skb->dev, &fl6, skb, flags);
-	} else {
+	} else if (tbl_id) {
 		struct fib6_table *table;
 
 		table = fib6_get_table(net, tbl_id);
 		if (!table)
 			goto out;
 
-		rt = ip6_pol_route(net, table, 0, &fl6, skb, flags);
+		rt = ip6_pol_route(net, table, oif, &fl6, skb, flags);
 		dst = &rt->dst;
+	} else {
+		dst = ip6_route_output(net, NULL, &fl6);
 	}
 
 	/* we want to discard traffic destined for local packet processing,
@@ -330,7 +333,7 @@ seg6_lookup_any_nexthop(struct sk_buff *skb, struct in6_addr *nhaddr,
 int seg6_lookup_nexthop(struct sk_buff *skb,
 			struct in6_addr *nhaddr, u32 tbl_id)
 {
-	return seg6_lookup_any_nexthop(skb, nhaddr, tbl_id, false);
+	return seg6_lookup_any_nexthop(skb, nhaddr, tbl_id, false, 0);
 }
 
 static __u8 seg6_flv_lcblock_octects(const struct seg6_flavors_info *finfo)
@@ -418,7 +421,7 @@ static int end_next_csid_core(struct sk_buff *skb, struct seg6_local_lwt *slwt)
 static int input_action_end_x_finish(struct sk_buff *skb,
 				     struct seg6_local_lwt *slwt)
 {
-	seg6_lookup_nexthop(skb, &slwt->nh6, 0);
+	seg6_lookup_any_nexthop(skb, &slwt->nh6, 0, false, slwt->oif);
 
 	return dst_input(skb);
 }
@@ -1277,15 +1280,15 @@ static int input_action_end_dt6(struct sk_buff *skb,
 	/* note: this time we do not need to specify the table because the VRF
 	 * takes care of selecting the correct table.
 	 */
-	seg6_lookup_any_nexthop(skb, NULL, 0, true);
+	seg6_lookup_any_nexthop(skb, NULL, 0, true, 0);
 
 	return dst_input(skb);
 
 legacy_mode:
 #endif
 	skb_set_transport_header(skb, sizeof(struct ipv6hdr));
 
-	seg6_lookup_any_nexthop(skb, NULL, slwt->table, true);
+	seg6_lookup_any_nexthop(skb, NULL, slwt->table, true, 0);
 
 	return dst_input(skb);
 
@@ -1477,7 +1480,8 @@ static struct seg6_action_desc seg6_action_table[] = {
 		.action		= SEG6_LOCAL_ACTION_END_X,
 		.attrs		= SEG6_F_ATTR(SEG6_LOCAL_NH6),
 		.optattrs	= SEG6_F_LOCAL_COUNTERS |
-				  SEG6_F_LOCAL_FLAVORS,
+				  SEG6_F_LOCAL_FLAVORS |
+				  SEG6_F_ATTR(SEG6_LOCAL_OIF),
 		.input		= input_action_end_x,
 	},
 	{

tools/testing/selftests/net/srv6_end_x_next_csid_l3vpn_test.sh

@@ -72,6 +72,9 @@
 # Every fcf0:0:x:y::/64 network interconnects the SRv6 routers rt-x with rt-y in
 # the selftest network.
 #
+# In addition, every router interface connecting rt-x to rt-y is assigned an
+# IPv6 link-local address fe80::x:y/64.
+#
 # Local SID/C-SID table
 # =====================
 #
@@ -521,6 +524,9 @@ setup_rt_networking()
 		ip -netns "${nsname}" addr \
 			add "${net_prefix}::${rt}/64" dev "${devname}" nodad
 
+		ip -netns "${nsname}" addr \
+			add "fe80::${rt}:${neigh}/64" dev "${devname}" nodad
+
 		ip -netns "${nsname}" link set "${devname}" up
 	done
 
@@ -609,6 +615,27 @@ set_end_x_nextcsid()
 		nflen "${LCNODEFUNC_BLEN}" dev "${DUMMY_DEVNAME}"
 }
 
+set_end_x_ll_nextcsid()
+{
+	local rt="$1"
+	local adj="$2"
+
+	eval nsname=\${$(get_rtname "${rt}")}
+	lcnode_func_prefix="$(build_lcnode_func_prefix "${rt}")"
+	nh6_ll_addr="fe80::${adj}:${rt}"
+	oifname="veth-rt-${rt}-${adj}"
+
+	# enabled NEXT-C-SID SRv6 End.X behavior via an IPv6 link-local nexthop
+	# address (note that "dev" is the dummy dum0 device chosen for the sake
+	# of simplicity).
+	ip -netns "${nsname}" -6 route \
+		replace "${lcnode_func_prefix}" \
+		table "${LOCALSID_TABLE_ID}" \
+		encap seg6local action End.X nh6 "${nh6_ll_addr}" \
+		oif "${oifname}" flavors next-csid lblen "${LCBLOCK_BLEN}" \
+		nflen "${LCNODEFUNC_BLEN}" dev "${DUMMY_DEVNAME}"
+}
+
 set_underlay_sids_reachability()
 {
 	local rt="$1"
@@ -1016,6 +1043,27 @@ host_vpn_tests()
 
 	check_and_log_hs_ipv4_connectivity 1 2
 	check_and_log_hs_ipv4_connectivity 2 1
+
+	# Setup the adjacencies in the SRv6 aware routers using IPv6 link-local
+	# addresses.
+	# - rt-3 SRv6 End.X adjacency with rt-4
+	# - rt-4 SRv6 End.X adjacency with rt-1
+	set_end_x_ll_nextcsid 3 4
+	set_end_x_ll_nextcsid 4 1
+
+	log_section "SRv6 VPN connectivity test hosts (h1 <-> h2, IPv6), link-local"
+
+	check_and_log_hs_ipv6_connectivity 1 2
+	check_and_log_hs_ipv6_connectivity 2 1
+
+	log_section "SRv6 VPN connectivity test hosts (h1 <-> h2, IPv4), link-local"
+
+	check_and_log_hs_ipv4_connectivity 1 2
+	check_and_log_hs_ipv4_connectivity 2 1
+
+	# Restore the previous adjacencies.
+	set_end_x_nextcsid 3 4
+	set_end_x_nextcsid 4 1
 }
 
 __nextcsid_end_x_behavior_test()