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Date:   Wed, 21 Sep 2022 10:15:18 +0300
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Subject: Re: [PATCH v5 net-next 6/6] selftests: forwarding: add test of
 MAC-Auth Bypass to locked port tests
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On Tue, Sep 20, 2022 at 11:29:12PM +0200, netdev@kapio-technology.com wrote:
> I have made a blackhole selftest, which looks like this:
> 
> test_blackhole_fdb()
> {
>         RET=0
> 
>         check_blackhole_fdb_support || return 0
> 
>         tcpdump_start $h2
>         $MZ $h1 -q -t udp -a $h1 -b $h2

I don't think you can give an interface name to '-a' and '-b'?

>         tcpdump_stop
>         tcpdump_show | grep -q udp
>         check_err $? "test_blackhole_fdb: No packet seen on initial"
>         tcpdump_cleanup
> 
>         bridge fdb add `mac_get $h2` dev br0 blackhole
>         bridge fdb show dev br0 | grep -q "blackhole"

Make this grep more specific so that we are sure it is the entry user
space installed. Something like this:

bridge fdb get `mac_get $h2` br br0 | grep -q blackhole

>         check_err $? "test_blackhole_fdb: No blackhole FDB entry found"
> 
>         tcpdump_start $h2
>         $MZ $h1 -q -t udp -a $h1 -b $h2
>         tcpdump_stop
>         tcpdump_show | grep -q udp
>         check_fail $? "test_blackhole_fdb: packet seen with blackhole fdb
> entry"
>         tcpdump_cleanup

The tcpdump filter is not specific enough. It can catch other UDP
packets (e.g., multicast) being received by $h2. Anyway, to be sure the
feature works as expected we need to make sure that the packets are not
even egressing $swp2. Checking that they are not received by $h2 is not
enough. See this (untested) suggestion [1] that uses a tc filter on the
egress of $swp2.

> 
>         bridge fdb del `mac_get $h2` dev br0 blackhole
>         bridge fdb show dev br0 | grep -q "blackhole"
>         check_fail $? "test_blackhole_fdb: Blackhole FDB entry not deleted"
> 
>         tcpdump_start $h2
>         $MZ $h1 -q -t udp -a $h1 -b $h2
>         tcpdump_stop
>         tcpdump_show | grep -q udp
>         check_err $? "test_blackhole_fdb: No packet seen after removing
> blackhole FDB entry"
>         tcpdump_cleanup
> 
>         log_test "Blackhole FDB entry test"
> }
> 
> the setup is simple and is the same as in bridge_sticky_fdb.sh.
> 
> Does the test look sound or is there obvious mistakes?

[1]
blackhole_fdb()
{
	RET=0

	tc filter add dev $swp2 egress protocol ip pref 1 handle 1 flower \
		dst_ip 192.0.2.2 ip_proto udp dst_port 12345 action pass

	$MZ $h1 -c 1 -p 128 -t udp "sp=54321,dp=12345" \
		-a own -b `mac_get $h2` -A 192.0.2.1 -B 192.0.2.2 -q

	tc_check_packets "dev $swp2 egress" 1 1
	check_err $? "Packet not seen on egress before adding blackhole entry"

	bridge fdb add `mac_get $h2` dev br0 blackhole
	bridge fdb get `mac_get $h2` br br0 | grep -q blackhole
	check_err $? "Blackhole entry not found"

	$MZ $h1 -c 1 -p 128 -t udp "sp=54321,dp=12345" \
		-a own -b `mac_get $h2` -A 192.0.2.1 -B 192.0.2.2 -q

	tc_check_packets "dev $swp2 egress" 1 1
	check_err $? "Packet seen on egress after adding blackhole entry"

	# Check blackhole entries can be replaced.
	bridge fdb replace `mac_get $h2` dev $swp2 master static
	bridge fdb get `mac_get $h2` br br0 | grep -q blackhole
	check_fail $? "Blackhole entry found after replacement"

	$MZ $h1 -c 1 -p 128 -t udp "sp=54321,dp=12345" \
		-a own -b `mac_get $h2` -A 192.0.2.1 -B 192.0.2.2 -q

	tc_check_packets "dev $swp2 egress" 1 2
	check_err $? "Packet not seen on egress after replacing blackhole entry"

	bridge fdb del `mac_get $h2` dev $swp2 master static
	tc filter del dev $swp2 egress protocol ip pref 1 handle 1 flower

	log_test "Blackhole FDB entry"
}