selftest: Add selftest for multicast address notifications

This commit adds a new kernel selftest to verify RTNLGRP_IPV4_MCADDR
and RTNLGRP_IPV6_MCADDR notifications. The test works by adding and
removing a dummy interface and then confirming that the system
correctly receives join and removal notifications for the 224.0.0.1
and ff02::1 multicast addresses.

The test relies on the iproute2 version to be 6.13+.

Tested by the following command:
$ vng -v --user root --cpus 16 -- \
make -C tools/testing/selftests TARGETS=net
TEST_PROGS=rtnetlink_notification.sh \
TEST_GEN_PROGS="" run_tests

Cc: Maciej Żenczykowski <maze@google.com>
Cc: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Yuyang Huang <yuyanghuang@google.com>
Link: https://patch.msgid.link/20250614053522.623820-1-yuyanghuang@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 71 insertions, 0 deletions

diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index ab996bd22a5f..3abb74d563a7 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -41,6 +41,7 @@ TEST_PROGS += netns-name.sh
 TEST_PROGS += link_netns.py
 TEST_PROGS += nl_netdev.py
 TEST_PROGS += rtnetlink.py
+TEST_PROGS += rtnetlink_notification.sh
 TEST_PROGS += srv6_end_dt46_l3vpn_test.sh
 TEST_PROGS += srv6_end_dt4_l3vpn_test.sh
 TEST_PROGS += srv6_end_dt6_l3vpn_test.sh
diff --git a/tools/testing/selftests/net/rtnetlink_notification.sh b/tools/testing/selftests/net/rtnetlink_notification.sh
new file mode 100755
index 000000000000..39c1b815bbe4
--- /dev/null
+++ b/tools/testing/selftests/net/rtnetlink_notification.sh
@@ -0,0 +1,70 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# This test is for checking rtnetlink notification callpaths, and get as much
+# coverage as possible.
+#
+# set -e
+
+ALL_TESTS="
+	kci_test_mcast_addr_notification
+"
+
+source lib.sh
+
+kci_test_mcast_addr_notification()
+{
+	RET=0
+	local tmpfile
+	local monitor_pid
+	local match_result
+	local test_dev="test-dummy1"
+
+	tmpfile=$(mktemp)
+	defer rm "$tmpfile"
+
+	ip monitor maddr > $tmpfile &
+	monitor_pid=$!
+	defer kill_process "$monitor_pid"
+
+	sleep 1
+
+	if [ ! -e "/proc/$monitor_pid" ]; then
+		RET=$ksft_skip
+		log_test "mcast addr notification: iproute2 too old"
+		return $RET
+	fi
+
+	ip link add name "$test_dev" type dummy
+	check_err $? "failed to add dummy interface"
+	ip link set "$test_dev" up
+	check_err $? "failed to set dummy interface up"
+	ip link del dev "$test_dev"
+	check_err $? "Failed to delete dummy interface"
+	sleep 1
+
+	# There should be 4 line matches as follows.
+	# 13: test-dummy1    inet6 mcast ff02::1 scope global 
+	# 13: test-dummy1    inet mcast 224.0.0.1 scope global 
+	# Deleted 13: test-dummy1    inet mcast 224.0.0.1 scope global 
+	# Deleted 13: test-dummy1    inet6 mcast ff02::1 scope global 
+	match_result=$(grep -cE "$test_dev.*(224.0.0.1|ff02::1)" "$tmpfile")
+	if [ "$match_result" -ne 4 ]; then
+		RET=$ksft_fail
+	fi
+	log_test "mcast addr notification: Expected 4 matches, got $match_result"
+	return $RET
+}
+
+#check for needed privileges
+if [ "$(id -u)" -ne 0 ];then
+	RET=$ksft_skip
+	log_test "need root privileges"
+	exit $RET
+fi
+
+require_command ip
+
+tests_run
+
+exit $EXIT_STATUS