linux-kernel - Re: [PATCH v4 net-next 5/6] net: dsa: mv88e6xxx: mac-auth/MAB implementation

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Date:   Thu, 21 Jul 2022 15:04:59 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     netdev@...io-technology.com
Cc:     davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Shuah Khan <shuah@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Ido Schimmel <idosch@...dia.com>, linux-kernel@...r.kernel.org,
        bridge@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 net-next 5/6] net: dsa: mv88e6xxx: mac-auth/MAB
 implementation

On Sun, Jul 17, 2022 at 02:34:22PM +0200, netdev@...io-technology.com wrote:
> > If I were to randomly guess at almost 4AM in the morning, it has to do with
> > "bridge fdb add" rather than the "bridge fdb replace" that's used for
> > the MAB selftest. The fact I pointed out a few revisions ago, that MAB
> > needs to be opt-in, is now coming back to bite us. Since it's not
> > opt-in, the mv88e6xxx driver always creates locked FDB entries, and when
> > we try to "bridge fdb add", the kernel says "hey, the FDB entry is
> > already there!". Is that it?
> 
> Yes, that sounds like a reasonable explanation, as it adds 'ext learned,
> offloaded' entries. If you try and replace the 'add' with 'replace' in those
> tests, does it work?

Well, you have access to the selftests too... But yes, that is the
reason, and it works when I change 'add' to 'replace', although of
course this isn't the correct solution.

> > As for how to opt into MAB. Hmm. MAB seems to be essentially CPU
> > assisted learning, which creates locked FDB entries. I wonder whether we
> > should reconsider the position that address learning makes no sense on
> > locked ports, and say that "+locked -learning" means no MAB, and
> > "+locked +learning" means MAB? This would make a bunch of things more
> > natural to handle in the kernel, and would also give us the opt-in we
> > need.
> 
> I have done the one and then the other. We need to have some final decision
> on this point. And remember that this gave rise to an extra patch to fix
> link-local learning if learning is turned on on a locked port, which
> resulted in the decision to allways have learning off on locked ports.

I think part of the reason for the back-and-forth was not making a very
clear distinction between basic 802.1X using hostapd, and MAB. While I
agree hostapd doesn't have what to do with learning, for MAB I'm still
wondering. It's the same situation for mv88e6xxx's Port Association
Vector in fact.

> > Side note, the VTU and ATU member violation printks annoy me so badly.
> > They aren't stating something super useful and they're a DoS attack
> > vector in itself, even if they're rate limited. I wonder whether we
> > could just turn the prints into a set of ethtool counters and call it a
> > day?
> 
> Sounds like a good idea to me. :-)

Thinking this through, what we really want is trace points here,
otherwise we'd lose information about which MAC address/VID/FID was it
that caused the violation.