[PATCH 1/7] seg6: add End.MAP behavior

Yuya Kusakabe
2026-05-03T16:26:17Z

Add the End.MAP behavior (RFC 9433 Section 6.2): an endpoint that
replaces the IPv6 destination address with a configured next SID
and forwards via IPv6 routing without consuming the SRH. The new
nh6 attribute selects the replacement SID.

Add three drop reasons that End.MAP emits to dropreason-core.h, so
dropped packets show up in the standard skb:kfree_skb tracepoint:

SEG6_MOBILE_INVALID_SRH_SL
SEG6_MOBILE_HOP_LIMIT_EXCEEDED
SEG6_MOBILE_NOMEM

Configuration:

ip -6 route add 2001:db8:f::/64 \
encap seg6local action End.MAP nh6 2001:db8:1::e \
dev <dev>

Link: https://www.rfc-editor.org/rfc/rfc9433.html#section-6.2
Signed-off-by: Yuya Kusakabe <yuya.kusakabe@gmail.com>
---
include/net/dropreason-core.h | 19 +++++
include/uapi/linux/seg6_local.h | 2 +
net/ipv6/seg6_local.c | 81 ++++++++++++++++++
tools/testing/selftests/net/Makefile | 1 +
tools/testing/selftests/net/srv6_end_map_test.sh | 102 +++++++++++++++++++++++
5 files changed, 205 insertions(+)

diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index e0ca3904ff8e..17f881009336 100644
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h
@@ -127,6 +127,9 @@
FN(PSP_INPUT) \
FN(PSP_OUTPUT) \
FN(RECURSION_LIMIT) \
+ FN(SEG6_MOBILE_INVALID_SRH_SL) \
+ FN(SEG6_MOBILE_HOP_LIMIT_EXCEEDED) \
+ FN(SEG6_MOBILE_NOMEM) \
FNe(MAX)

/**
@@ -600,6 +603,22 @@ enum skb_drop_reason {
SKB_DROP_REASON_PSP_OUTPUT,
/** @SKB_DROP_REASON_RECURSION_LIMIT: Dead loop on virtual device. */
SKB_DROP_REASON_RECURSION_LIMIT,
+ /**
+ * @SKB_DROP_REASON_SEG6_MOBILE_INVALID_SRH_SL: invalid Segments Left
+ * value or SRH validation failure on an SRv6 Mobile path.
+ */
+ SKB_DROP_REASON_SEG6_MOBILE_INVALID_SRH_SL,
+ /**
+ * @SKB_DROP_REASON_SEG6_MOBILE_HOP_LIMIT_EXCEEDED: outer IPv6 Hop
+ * Limit reached zero on an SRv6 Mobile forwarding path (e.g.
+ * End.MAP).
+ */
+ SKB_DROP_REASON_SEG6_MOBILE_HOP_LIMIT_EXCEEDED,
+ /**
+ * @SKB_DROP_REASON_SEG6_MOBILE_NOMEM: skb head/tail expansion or
+ * helper allocation failed on an SRv6 Mobile path.
+ */
+ SKB_DROP_REASON_SEG6_MOBILE_NOMEM,
/**
* @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which
* shouldn't be used as a real 'reason' - only for tracing code gen
diff --git a/include/uapi/linux/seg6_local.h b/include/uapi/linux/seg6_local.h
index 4fdc424c9cb3..45386fdfa821 100644
--- a/include/uapi/linux/seg6_local.h
+++ b/include/uapi/linux/seg6_local.h
@@ -67,6 +67,8 @@ enum {
SEG6_LOCAL_ACTION_END_BPF = 15,
/* decap and lookup of DA in v4 or v6 table */
SEG6_LOCAL_ACTION_END_DT46 = 16,
+ /* swap DA with new SID, leave SRH untouched (RFC 9433 Section 6.2) */
+ SEG6_LOCAL_ACTION_END_MAP = 17,

__SEG6_LOCAL_ACTION_MAX,
};
diff --git a/net/ipv6/seg6_local.c b/net/ipv6/seg6_local.c
index 2b41e4c0dddd..cebecbe5e49b 100644
--- a/net/ipv6/seg6_local.c
+++ b/net/ipv6/seg6_local.c
@@ -1468,6 +1468,81 @@ static int input_action_end_bpf(struct sk_buff *skb,
return -EINVAL;
}

+/* SRH validation helper for SRv6 Mobile (RFC 9433) behaviors that may
+ * receive an SRv6 encapsulated packet. Returns the SRH on success or
+ * NULL on validation failure / when the SRH is absent. The caller
+ * uses @missing to distinguish the two NULL cases: an SRH-less packet
+ * may be acceptable depending on the behavior.
+ */
+static struct ipv6_sr_hdr *seg6_mobile_get_validated_srh(struct sk_buff *skb,
+ bool *missing)
+{
+ struct ipv6_sr_hdr *srh = seg6_get_srh(skb, 0);
+
+ if (!srh) {
+ if (missing)
+ *missing = true;
+ return NULL;
+ }
+ if (missing)
+ *missing = false;
+
+#ifdef CONFIG_IPV6_SEG6_HMAC
+ if (!seg6_hmac_validate_skb(skb))
+ return NULL;
+#endif
+ return srh;
+}
+
+/* RFC 9433 Section 6.2 -- End.MAP
+ * Replace the outer IPv6 destination address with the configured next
+ * SID, decrement the Hop Limit, and forward via IPv6 routing. The
+ * SRH is left untouched, so any subsequent End* behavior continues to
+ * see the original Segment List unchanged.
+ */
+static int input_action_end_map(struct sk_buff *skb,
+ struct seg6_local_lwt *slwt)
+{
+ enum skb_drop_reason reason;
+ struct ipv6_sr_hdr *srh;
+ struct ipv6hdr *ip6h;
+ bool no_srh = false;
+
+ reason = SKB_DROP_REASON_SEG6_MOBILE_INVALID_SRH_SL;
+
+ /* When an SRH is present it must HMAC-validate before we touch
+ * the destination; an SRH-less packet is also accepted because
+ * End.MAP does not consume the SRH.
+ */
+ srh = seg6_mobile_get_validated_srh(skb, &no_srh);
+ if (!srh && !no_srh)
+ goto drop;
+
+ if (skb_ensure_writable(skb, sizeof(*ip6h))) {
+ reason = SKB_DROP_REASON_SEG6_MOBILE_NOMEM;
+ goto drop;
+ }
+
+ ip6h = ipv6_hdr(skb);
+
+ if (ip6h->hop_limit <= 1) {
+ icmpv6_send(skb, ICMPV6_TIME_EXCEED, ICMPV6_EXC_HOPLIMIT, 0);
+ reason = SKB_DROP_REASON_SEG6_MOBILE_HOP_LIMIT_EXCEEDED;
+ goto drop;
+ }
+
+ ip6h->hop_limit--;
+ ip6h->daddr = slwt->nh6;
+
+ skb_dst_drop(skb);
+ seg6_lookup_nexthop(skb, NULL, 0);
+ return dst_input(skb);
+
+drop:
+ kfree_skb_reason(skb, reason);
+ return -EINVAL;
+}
+
static struct seg6_action_desc seg6_action_table[] = {
{
.action = SEG6_LOCAL_ACTION_END,
@@ -1565,6 +1640,12 @@ static struct seg6_action_desc seg6_action_table[] = {
.optattrs = SEG6_F_LOCAL_COUNTERS,
.input = input_action_end_bpf,
},
+ {
+ .action = SEG6_LOCAL_ACTION_END_MAP,
+ .attrs = SEG6_F_ATTR(SEG6_LOCAL_NH6),
+ .optattrs = SEG6_F_LOCAL_COUNTERS,
+ .input = input_action_end_map,
+ },

};

diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index a275ed584026..b43e87e36174 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -84,6 +84,7 @@ TEST_PROGS := \
sctp_vrf.sh \
skf_net_off.sh \
so_txtime.sh \
+ srv6_end_map_test.sh \
srv6_end_dt46_l3vpn_test.sh \
srv6_end_dt4_l3vpn_test.sh \
srv6_end_dt6_l3vpn_test.sh \
diff --git a/tools/testing/selftests/net/srv6_end_map_test.sh b/tools/testing/selftests/net/srv6_end_map_test.sh
new file mode 100755
index 000000000000..4e3b63699388
--- /dev/null
+++ b/tools/testing/selftests/net/srv6_end_map_test.sh
@@ -0,0 +1,102 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Selftest for the SRv6 End.MAP behavior (RFC 9433 Section 6.2).
+#
+# +--------+ 2001:db8:1::/64 +--------+ 2001:db8:2::/64 +--------+
+# | srupf1 | ------------------- | srupf2 | ------------------- | srupf3 |
+# +--------+ veth-1 +--------+ veth-2 +--------+
+# (intermediate
+# SRv6-aware UPF,
+# End.MAP)
+#
+# All three netns are SRv6-aware UPFs in the RFC 9433 sense (not
+# 3GPP UPFs). Per RFC 9433 Section 6.2 End.MAP is used by the
+# intermediate UPF (here srupf2): srupf2 has an End.MAP SID for
+# locator 2001:db8:f::/64 mapping to the new SID 2001:db8:2::e.
+# srupf1 sends an IPv6 packet to 2001:db8:f::1; on srupf3 the
+# destination address is expected to have been replaced by
+# 2001:db8:2::e.
+
+source lib.sh
+
+readonly TIMEOUT=4
+
+cleanup()
+{
+ cleanup_all_ns
+}
+
+trap cleanup EXIT
+
+setup()
+{
+ setup_ns srupf1 srupf2 srupf3
+
+ ip -n "$srupf1" link set lo up
+ ip -n "$srupf2" link set lo up
+ ip -n "$srupf3" link set lo up
+
+ ip link add veth-1 netns "$srupf1" type veth peer name veth-1-srupf2 \
+ netns "$srupf2"
+ ip -n "$srupf1" addr add 2001:db8:1::1/64 dev veth-1 nodad
+ ip -n "$srupf2" addr add 2001:db8:1::2/64 dev veth-1-srupf2 nodad
+ ip -n "$srupf1" link set veth-1 up
+ ip -n "$srupf2" link set veth-1-srupf2 up
+
+ ip link add veth-2 netns "$srupf2" type veth peer name veth-2-srupf3 \
+ netns "$srupf3"
+ ip -n "$srupf2" addr add 2001:db8:2::1/64 dev veth-2 nodad
+ ip -n "$srupf3" addr add 2001:db8:2::e/64 dev veth-2-srupf3 nodad
+ ip -n "$srupf2" link set veth-2 up
+ ip -n "$srupf3" link set veth-2-srupf3 up
+
+ ip netns exec "$srupf2" sysctl -wq net.ipv6.conf.all.forwarding=1
+
+ ip -n "$srupf1" -6 route add 2001:db8:f::/64 via 2001:db8:1::2
+
+ ip -n "$srupf2" -6 route add 2001:db8:f::/64 \
+ encap seg6local action End.MAP nh6 2001:db8:2::e \
+ dev veth-2
+
+ # allow srupf3 to reply back to srupf1
+ ip -n "$srupf3" -6 route add 2001:db8:1::/64 via 2001:db8:2::1
+}
+
+check_dependencies()
+{
+ if ! command -v ping >/dev/null; then
+ echo "SKIP: ping is required"; exit "$ksft_skip"
+ fi
+
+ if ! ip route help 2>&1 | grep -qF "End.MAP"; then
+ echo "SKIP: iproute2 too old, missing seg6local action End.MAP"
+ exit "$ksft_skip"
+ fi
+}
+
+run_test()
+{
+ # srupf3 replies to ICMPv6 echo on 2001:db8:2::e, so a successful
+ # ping from srupf1 to the End.MAP SID demonstrates that the action
+ # replaced the destination address with 2001:db8:2::e.
+ if ! ip netns exec "$srupf1" ping -6 -c 1 -W "$TIMEOUT" \
+ 2001:db8:f::1 >/dev/null 2>&1; then
+ return 1
+ fi
+ return 0
+}
+
+main()
+{
+ check_dependencies
+ setup
+
+ if run_test; then
+ echo "TEST: End.MAP [PASS]"; exit "$ksft_pass"
+ else
+ echo "TEST: End.MAP [FAIL]"; exit "$ksft_fail"
+ fi
+}
+
+main "$@"

--
2.50.1