selftests: net: Introduce first PMTU test

One single test implemented so far: test_pmtu_vti6_exception
checks that the PMTU of a route exception, caused by a tunnel
exceeding the link layer MTU, is affected by administrative
changes of the tunnel MTU. Creation of the route exception is
checked too.
Requested-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Acked-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/Makefile

@@ -5,7 +5,7 @@ CFLAGS =  -Wall -Wl,--no-as-needed -O2 -g
 CFLAGS += -I../../../../usr/include/
 
 TEST_PROGS := run_netsocktests run_afpackettests test_bpf.sh netdevice.sh rtnetlink.sh
-TEST_PROGS += fib_tests.sh fib-onlink-tests.sh
+TEST_PROGS += fib_tests.sh fib-onlink-tests.sh pmtu.sh
 TEST_GEN_FILES =  socket
 TEST_GEN_FILES += psock_fanout psock_tpacket msg_zerocopy
 TEST_GEN_PROGS = reuseport_bpf reuseport_bpf_cpu reuseport_bpf_numa

tools/testing/selftests/net/pmtu.sh

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Check that route PMTU values match expectations
+#
+# Tests currently implemented:
+#
+# - test_pmtu_vti6_exception
+#	Set up vti6 tunnel on top of veth, with xfrm states and policies, in two
+#	namespaces with matching endpoints. Check that route exception is
+#	created by exceeding link layer MTU with ping to other endpoint. Then
+#	decrease and increase MTU of tunnel, checking that route exception PMTU
+#	changes accordingly
+
+NS_A="ns-$(mktemp -u XXXXXX)"
+NS_B="ns-$(mktemp -u XXXXXX)"
+ns_a="ip netns exec ${NS_A}"
+ns_b="ip netns exec ${NS_B}"
+
+veth6_a_addr="fd00:1::a"
+veth6_b_addr="fd00:1::b"
+veth6_mask="64"
+
+vti6_a_addr="fd00:2::a"
+vti6_b_addr="fd00:2::b"
+vti6_mask="64"
+
+setup_namespaces() {
+	ip netns add ${NS_A} || return 0
+	ip netns add ${NS_B}
+
+	return 1
+}
+
+setup_veth() {
+	${ns_a} ip link add veth_a type veth peer name veth_b || return 0
+	${ns_a} ip link set veth_b netns ${NS_B}
+
+	${ns_a} ip addr add ${veth6_a_addr}/${veth6_mask} dev veth_a
+	${ns_b} ip addr add ${veth6_b_addr}/${veth6_mask} dev veth_b
+
+	${ns_a} ip link set veth_a up
+	${ns_b} ip link set veth_b up
+
+	return 1
+}
+
+setup_vti6() {
+	${ns_a} ip link add vti_a type vti6 local ${veth6_a_addr} remote ${veth6_b_addr} key 10 || return 0
+	${ns_b} ip link add vti_b type vti6 local ${veth6_b_addr} remote ${veth6_a_addr} key 10
+
+	${ns_a} ip addr add ${vti6_a_addr}/${vti6_mask} dev vti_a
+	${ns_b} ip addr add ${vti6_b_addr}/${vti6_mask} dev vti_b
+
+	${ns_a} ip link set vti_a up
+	${ns_b} ip link set vti_b up
+
+	sleep 1
+
+	return 1
+}
+
+setup_xfrm() {
+	${ns_a} ip -6 xfrm state add src ${veth6_a_addr} dst ${veth6_b_addr} spi 0x1000 proto esp aead "rfc4106(gcm(aes))" 0x0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f 128 mode tunnel || return 0
+	${ns_a} ip -6 xfrm state add src ${veth6_b_addr} dst ${veth6_a_addr} spi 0x1001 proto esp aead "rfc4106(gcm(aes))" 0x0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f 128 mode tunnel
+	${ns_a} ip -6 xfrm policy add dir out mark 10 tmpl src ${veth6_a_addr} dst ${veth6_b_addr} proto esp mode tunnel
+	${ns_a} ip -6 xfrm policy add dir in mark 10 tmpl src ${veth6_b_addr} dst ${veth6_a_addr} proto esp mode tunnel
+
+	${ns_b} ip -6 xfrm state add src ${veth6_a_addr} dst ${veth6_b_addr} spi 0x1000 proto esp aead "rfc4106(gcm(aes))" 0x0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f 128 mode tunnel
+	${ns_b} ip -6 xfrm state add src ${veth6_b_addr} dst ${veth6_a_addr} spi 0x1001 proto esp aead "rfc4106(gcm(aes))" 0x0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f 128 mode tunnel
+	${ns_b} ip -6 xfrm policy add dir out mark 10 tmpl src ${veth6_b_addr} dst ${veth6_a_addr} proto esp mode tunnel
+	${ns_b} ip -6 xfrm policy add dir in mark 10 tmpl src ${veth6_a_addr} dst ${veth6_b_addr} proto esp mode tunnel
+
+	return 1
+}
+
+setup() {
+	tunnel_type="$1"
+
+	[ "$(id -u)" -ne 0 ] && echo "SKIP: need to run as root" && exit 0
+
+	setup_namespaces && echo "SKIP: namespaces not supported" && exit 0
+	setup_veth && echo "SKIP: veth not supported" && exit 0
+
+	case ${tunnel_type} in
+	"vti6")
+		setup_vti6 && echo "SKIP: vti6 not supported" && exit 0
+		setup_xfrm && echo "SKIP: xfrm not supported" && exit 0
+		;;
+	*)
+		;;
+	esac
+}
+
+cleanup() {
+	ip netns del ${NS_A} 2 > /dev/null
+	ip netns del ${NS_B} 2 > /dev/null
+}
+
+mtu() {
+	ns_cmd="${1}"
+	dev="${2}"
+	mtu="${3}"
+
+	${ns_cmd} ip link set dev ${dev} mtu ${mtu}
+}
+
+route_get_dst_exception() {
+	dst="${1}"
+
+	${ns_a} ip route get "${dst}"
+}
+
+route_get_dst_pmtu_from_exception() {
+	dst="${1}"
+
+	exception="$(route_get_dst_exception ${dst})"
+	next=0
+	for i in ${exception}; do
+		[ ${next} -eq 1 ] && echo "${i}" && return
+		[ "${i}" = "mtu" ] && next=1
+	done
+}
+
+test_pmtu_vti6_exception() {
+	setup vti6
+
+	# Create route exception by exceeding link layer MTU
+	mtu "${ns_a}" veth_a 4000
+	mtu "${ns_b}" veth_b 4000
+	mtu "${ns_a}" vti_a 5000
+	mtu "${ns_b}" vti_b 5000
+	${ns_a} ping6 -q -i 0.1 -w 2 -s 60000 ${vti6_b_addr} > /dev/null
+
+	# Check that exception was created
+	if [ "$(route_get_dst_pmtu_from_exception ${vti6_b_addr})" = "" ]; then
+		echo "FAIL: Tunnel exceeding link layer MTU didn't create route exception"
+		exit 1
+	fi
+
+	# Decrease tunnel MTU, check for PMTU decrease in route exception
+	mtu "${ns_a}" vti_a 3000
+
+	if [ "$(route_get_dst_pmtu_from_exception ${vti6_b_addr})" -ne 3000 ]; then
+		echo "FAIL: Decreasing tunnel MTU didn't decrease route exception PMTU"
+		exit 1
+	fi
+
+	# Increase tunnel MTU, check for PMTU increase in route exception
+	mtu "${ns_a}" vti_a 9000
+	if [ "$(route_get_dst_pmtu_from_exception ${vti6_b_addr})" -ne 9000 ]; then
+		echo "FAIL: Increasing tunnel MTU didn't increase route exception PMTU"
+		exit 1
+	fi
+
+	echo "PASS"
+}
+
+trap cleanup EXIT
+
+test_pmtu_vti6_exception
+
+exit 0