selftests: net: add tests for PPPoL2TP

Add ping, iperf3, and recursion tests for PPPoL2TP.

Assisted-by: Gemini:gemini-3-flash
Signed-off-by: Qingfang Deng <qingfang.deng@linux.dev>
Link: https://patch.msgid.link/20260514015743.37869-1-qingfang.deng@linux.dev
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

tools/testing/selftests/net/ppp/Makefile

@@ -5,6 +5,7 @@ top_srcdir = ../../../../..
 TEST_PROGS := \
 	ppp_async.sh \
 	pppoe.sh \
+	pppol2tp.sh \
 # end of TEST_PROGS
 
 TEST_FILES := \

tools/testing/selftests/net/ppp/config

@@ -1,4 +1,5 @@
 CONFIG_IPV6=y
+CONFIG_L2TP=m
 CONFIG_PACKET=y
 CONFIG_PPP=m
 CONFIG_PPP_ASYNC=m
@@ -6,4 +7,5 @@ CONFIG_PPP_BSDCOMP=m
 CONFIG_PPP_DEFLATE=m
 CONFIG_PPPOE=m
 CONFIG_PPPOE_HASH_BITS_4=y
+CONFIG_PPPOL2TP=m
 CONFIG_VETH=y

tools/testing/selftests/net/ppp/pppol2tp.sh

@@ -0,0 +1,95 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+source ppp_common.sh
+
+VETH_SERVER="veth-server"
+VETH_CLIENT="veth-client"
+OUTER_IP_SERVER="172.16.1.1"
+OUTER_IP_CLIENT="172.16.1.2"
+
+PPPOL2TP_DIR=$(mktemp -d /tmp/pppol2tp.XXXXXX)
+
+# shellcheck disable=SC2329
+cleanup() {
+	cleanup_all_ns
+	rm -rf "$PPPOL2TP_DIR"
+}
+
+trap cleanup EXIT
+
+require_command xl2tpd
+ppp_common_init
+modprobe -q l2tp_ppp
+
+# Create the veth pair
+ip link add "$VETH_SERVER" type veth peer name "$VETH_CLIENT"
+ip link set "$VETH_SERVER" netns "$NS_SERVER"
+ip link set "$VETH_CLIENT" netns "$NS_CLIENT"
+ip -netns "$NS_SERVER" link set "$VETH_SERVER" up
+ip -netns "$NS_CLIENT" link set "$VETH_CLIENT" up
+ip -netns "$NS_SERVER" address add dev "$VETH_SERVER" "$OUTER_IP_SERVER" peer "$OUTER_IP_CLIENT"
+ip -netns "$NS_CLIENT" address add dev "$VETH_CLIENT" "$OUTER_IP_CLIENT" peer "$OUTER_IP_SERVER"
+
+# Generate configuration files
+cat > "$PPPOL2TP_DIR/l2tp-server.conf" <<EOF
+[global]
+listen-addr = $OUTER_IP_SERVER
+access control = no
+
+[lns default]
+ip range = $IP_CLIENT
+local ip = $IP_SERVER
+require authentication = no
+require chap = no
+require pap = no
+ppp debug = yes
+pppoptfile = $(pwd)/pppoe-server-options
+EOF
+
+cat > "$PPPOL2TP_DIR/l2tp-client.conf" <<EOF
+[global]
+listen-addr = $OUTER_IP_CLIENT
+access control = no
+
+[lac server]
+lns = $OUTER_IP_SERVER
+require authentication = no
+require chap = no
+require pap = no
+ppp debug = yes
+pppoptfile = $(pwd)/pppoe-server-options
+EOF
+
+# Start the L2TP Server
+ip netns exec "$NS_SERVER" xl2tpd -D -c "$PPPOL2TP_DIR/l2tp-server.conf" \
+	-p "$PPPOL2TP_DIR/l2tp-server.pid" -C "$PPPOL2TP_DIR/l2tp-server.control" &
+
+# Start the L2TP Client
+ip netns exec "$NS_CLIENT" xl2tpd -D -c "$PPPOL2TP_DIR/l2tp-client.conf" \
+	-p "$PPPOL2TP_DIR/l2tp-client.pid" -C "$PPPOL2TP_DIR/l2tp-client.control" &
+
+# Wait for xl2tpd to start and open their control pipes
+slowwait 2 [ -p "$PPPOL2TP_DIR/l2tp-server.control" ]
+slowwait 2 [ -p "$PPPOL2TP_DIR/l2tp-client.control" ]
+
+# Connect LAC to LNS
+echo "c server" > "$PPPOL2TP_DIR/l2tp-client.control"
+
+ppp_test_connectivity
+
+log_test "PPPoL2TP"
+
+# Recursion test
+RET=0
+# Delete route to LNS IP
+ip -netns "$NS_CLIENT" route del "$OUTER_IP_SERVER"
+# Add default route through ppp0
+ip -netns "$NS_CLIENT" route add default dev ppp0
+# ping (we expect the ping to fail but not deadlock the system)
+ip netns exec "$NS_CLIENT" ping -c 1 "$IP_SERVER" -w 1
+check_fail $?
+
+log_test "PPPoL2TP Recursion"
+
+exit "$EXIT_STATUS"