netdev - Re: [PATCH net v3 2/2] selftests: net: add test for destination in broadcast packets

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Message-ID: <7a5ef6e5-ea7f-41be-97c9-555666a3ef67@redhat.com>
Date: Thu, 28 Aug 2025 10:51:49 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Brett A C Sheffield <bacs@...recast.net>, Oscar Maes <oscmaes92@...il.com>
Cc: netdev@...r.kernel.org, kuba@...nel.org, davem@...emloft.net,
 dsahern@...nel.org, regressions@...ts.linux.dev, stable@...r.kernel.org
Subject: Re: [PATCH net v3 2/2] selftests: net: add test for destination in
 broadcast packets

On 8/27/25 4:26 PM, Brett A C Sheffield wrote:
> 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@...il.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@...recast.net>
> 
> to your commit message. I spend quite a bit of my Saturday bisecting and
> diagnosing,  and writing the patch and test.

I don't want to delay the fix, since I received other reports for the
same problem, but I think proper recognition should be agreed by all the
involved parties.

I'm going to apply patch 1/2 standalone, to allow repost for this one.

>>  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@...recast.net>
>> +# Author: Oscar Maes <oscmaes92@...il.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

Here you could use slowwait checking for packet socket creation, to be
more robust WRT very slow env.

/P