On 2025-08-27 08:23, Oscar Maes wrote:

Add test to check the broadcast ethernet destination field is set correctly.

This test sends a broadcast ping, captures it using tcpdump and ensures that all bits of the 6 octet ethernet destination address are correctly set by examining the output capture file.

Signed-off-by: Oscar Maes oscmaes92@gmail.com

Link to discussion: https://lore.kernel.org/netdev/20250822165231.4353-4-bacs@librecast.net/

Thanks to Brett Sheffield for writing the initial version of this selftest!

Thanks for leaving my author name in the file. Perhaps you might consider adding:

Co-Authored-By: Brett A C Sheffield bacs@librecast.net

to your commit message. I spend quite a bit of my Saturday bisecting and diagnosing, and writing the patch and test.

tools/testing/selftests/net/Makefile | 1 + .../selftests/net/broadcast_ether_dst.sh | 82 +++++++++++++++++++ 2 files changed, 83 insertions(+) create mode 100755 tools/testing/selftests/net/broadcast_ether_dst.sh

diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile index b31a71f2b372..56ad10ea6628 100644 --- a/tools/testing/selftests/net/Makefile +++ b/tools/testing/selftests/net/Makefile @@ -115,6 +115,7 @@ TEST_PROGS += skf_net_off.sh TEST_GEN_FILES += skf_net_off TEST_GEN_FILES += tfo TEST_PROGS += tfo_passive.sh +TEST_PROGS += broadcast_ether_dst.sh TEST_PROGS += broadcast_pmtu.sh TEST_PROGS += ipv6_force_forwarding.sh diff --git a/tools/testing/selftests/net/broadcast_ether_dst.sh b/tools/testing/selftests/net/broadcast_ether_dst.sh new file mode 100755 index 000000000000..865b5c7c8c8a --- /dev/null +++ b/tools/testing/selftests/net/broadcast_ether_dst.sh @@ -0,0 +1,82 @@ +#!/bin/bash +# SPDX-License-Identifier: GPL-2.0 +# +# Author: Brett A C Sheffield bacs@librecast.net +# Author: Oscar Maes oscmaes92@gmail.com +# +# Ensure destination ethernet field is correctly set for +# broadcast packets

+source lib.sh

+CLIENT_IP4="192.168.0.1" +GW_IP4="192.168.0.2"

+setup() {

• setup_ns CLIENT_NS SERVER_NS
• ip -net "${SERVER_NS}" link add link1 type veth \

• peer name link0 netns "${CLIENT_NS}"
  

• ip -net "${CLIENT_NS}" link set link0 up
• ip -net "${CLIENT_NS}" addr add "${CLIENT_IP4}"/24 dev link0
• ip -net "${SERVER_NS}" link set link1 up
• ip -net "${CLIENT_NS}" route add default via "${GW_IP4}"
• ip netns exec "${CLIENT_NS}" arp -s "${GW_IP4}" 00:11:22:33:44:55

+}

+cleanup() {

• rm -f "${CAPFILE}"
• ip -net "${SERVER_NS}" link del link1
• cleanup_ns "${CLIENT_NS}" "${SERVER_NS}"

+}

+test_broadcast_ether_dst() {

• local rc=0
• CAPFILE=$(mktemp -u cap.XXXXXXXXXX)
• echo "Testing ethernet broadcast destination"
• # start tcpdump listening for icmp
• # tcpdump will exit after receiving a single packet
• # timeout will kill tcpdump if it is still running after 2s
• timeout 2s ip netns exec "${CLIENT_NS}" \

• tcpdump -i link0 -c 1 -w "${CAPFILE}" icmp &> /dev/null &
  

• pid=$!
• sleep 0.1 # let tcpdump wake up
• # send broadcast ping
• ip netns exec "${CLIENT_NS}" \

• ping -W0.01 -c1 -b 255.255.255.255 &> /dev/null
  

• # wait for tcpdump for exit after receiving packet
• wait "${pid}"
• # compare ethernet destination field to ff:ff:ff:ff:ff:ff
• ether_dst=$(tcpdump -r "${CAPFILE}" -tnne 2>/dev/null | \

• 	awk '{sub(/,/,"",$3); print $3}')
  

• if [[ "${ether_dst}" == "ff:ff:ff:ff:ff:ff" ]]; then

• echo "[ OK ]"
  

• rc="${ksft_pass}"
  

• else

• echo "[FAIL] expected dst ether addr to be ff:ff:ff:ff:ff:ff," \
  

• 	"got ${ether_dst}"
  

• rc="${ksft_fail}"
  

• fi
• return "${rc}"

+}

+if [ ! -x "$(command -v tcpdump)" ]; then

• echo "SKIP: Could not run test without tcpdump tool"
• exit "${ksft_skip}"

+fi

+trap cleanup EXIT

+setup +test_broadcast_ether_dst

+exit $?

2.39.5