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Date:   Tue, 20 Sep 2022 23:29:12 +0200
From:   netdev@kapio-technology.com
To:     Ido Schimmel <idosch@nvidia.com>
Cc:     Vladimir Oltean <olteanv@gmail.com>, davem@davemloft.net,
        kuba@kernel.org, netdev@vger.kernel.org,
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        Roopa Prabhu <roopa@nvidia.com>,
        Nikolay Aleksandrov <razor@blackwall.org>,
        Shuah Khan <shuah@kernel.org>,
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        bridge@lists.linux-foundation.org, linux-kselftest@vger.kernel.org
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 2022-09-12 11:08, Ido Schimmel wrote:
> On Sun, Sep 11, 2022 at 11:23:55AM +0200, netdev@kapio-technology.com 
> wrote:
>> On 2022-09-11 02:13, Vladimir Oltean wrote:
>> > On Fri, Sep 09, 2022 at 03:11:56PM +0200, netdev@kapio-technology.com
>> > wrote:
>> > > > > > On Wed, Sep 07, 2022 at 11:10:07PM +0200, netdev@kapio-technology.com wrote:
>> > > > > > > I am at the blackhole driver implementation now, as I suppose that the
>> > > > > > > iproute2 command should work with the mv88e6xxx driver when adding blackhole
>> > > > > > > entries (with a added selftest)?
>> > > > > > > I decided to add the blackhole feature as new ops for drivers with functions
>> > > > > > > blackhole_fdb_add() and blackhole_fdb_del(). Do you agree with that approach?
>> > > > > >
>> > > > > > I assume you are talking about extending 'dsa_switch_ops'?
>> > > > >
>> > > > > Yes, that is the idea.
>> > > > >
>> > > > > > If so, it's up to the DSA maintainers to decide.
>> > > >
>> > > > What will be the usefulness of adding a blackhole FDB entry from user
>> > > > space?
>> > >
>> > > With the software bridge it could be used to signal a untrusted host
>> > > in
>> > > connection with a locked port entry attempt. I don't see so much use
>> > > other
>> > > that test purposes with the driver though.
>> >
>> > Not a huge selling point, to be honest. Can't the blackhole flag remain
>> > settable only in the device -> bridge direction, with user space just
>> > reading it?
>> 
>> That is possible, but it would of course not make sense to have 
>> selftests of
>> the feature as that would not work unless there is a driver with this
>> capability (now just mv88e6xxx).
> 
> The new "blackhole" flag requires changes in the bridge driver and
> without allowing user space to add such entries, the only way to test
> these changes is with mv88e6xxx which many of us do not have...

I am now building from new system (comp), and the kernel selftests are 
not being installed correctly, so I haven't been able to run the 
selftests yet.

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
         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"
         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

         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?