[PATCH net-next] selftest: Add selftest for multicast address notifications

[Yuyang Huang <yuyanghuang@google.com>]

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.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>
---
 tools/testing/selftests/net/rtnetlink.sh | 34 ++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/tools/testing/selftests/net/rtnetlink.sh b/tools/testing/selftests/net/rtnetlink.sh
index 2e8243a65b50..9dbcaaeaf8cd 100755
--- a/tools/testing/selftests/net/rtnetlink.sh
+++ b/tools/testing/selftests/net/rtnetlink.sh
@@ -21,6 +21,7 @@ ALL_TESTS="
 	kci_test_vrf
 	kci_test_encap
 	kci_test_macsec
+	kci_test_mcast_addr_notification
 	kci_test_ipsec
 	kci_test_ipsec_offload
 	kci_test_fdb_get
@@ -1334,6 +1335,39 @@ kci_test_mngtmpaddr()
 	return $ret
 }
 
+kci_test_mcast_addr_notification()
+{
+	local tmpfile
+	local monitor_pid
+	local match_result
+
+	tmpfile=$(mktemp)
+
+	ip monitor maddr > $tmpfile &
+	monitor_pid=$!
+	sleep 1
+
+	run_cmd ip link add name test-dummy1 type dummy
+	run_cmd ip link set test-dummy1 up
+	run_cmd ip link del dev test-dummy1
+	sleep 1
+
+	match_result=$(grep -cE "test-dummy1.*(224.0.0.1|ff02::1)" $tmpfile)
+
+	kill $monitor_pid
+	rm $tmpfile
+	# 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 
+	if [ $match_result -ne 4 ];then
+		end_test "FAIL: mcast addr notification"
+		return 1
+	fi
+	end_test "PASS: mcast addr notification"
+}
+
 kci_test_rtnl()
 {
 	local current_test
-- 
2.49.0.1204.g71687c7c1d-goog