Message-ID: <20220317161808.psftauoz5iaecduy@skbuf>
Date:   Thu, 17 Mar 2022 18:18:08 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Hans Schultz <schultz.hans@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, davem@...emloft.net, kuba@...nel.org,
        netdev@...r.kernel.org, Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Ido Schimmel <idosch@...dia.com>, linux-kernel@...r.kernel.org,
        bridge@...ts.linux-foundation.org
Subject: Re: [PATCH net-next 3/3] net: dsa: mv88e6xxx: mac-auth/MAB
 implementation

On Thu, Mar 17, 2022 at 05:07:15PM +0100, Hans Schultz wrote:
> On tor, mar 17, 2022 at 17:36, Vladimir Oltean <olteanv@...il.com> wrote:
> > On Thu, Mar 17, 2022 at 03:19:46PM +0100, Andrew Lunn wrote:
> >> On Thu, Mar 17, 2022 at 09:52:15AM +0100, Hans Schultz wrote:
> >> > On tor, mar 17, 2022 at 01:34, Vladimir Oltean <olteanv@...il.com> wrote:
> >> > > On Mon, Mar 14, 2022 at 11:46:51AM +0100, Hans Schultz wrote:
> >> > >> >> @@ -396,6 +414,13 @@ static irqreturn_t mv88e6xxx_g1_atu_prob_irq_thread_fn(int irq, void *dev_id)
> >> > >> >>  				    "ATU miss violation for %pM portvec %x spid %d\n",
> >> > >> >>  				    entry.mac, entry.portvec, spid);
> >> > >> >>  		chip->ports[spid].atu_miss_violation++;
> >> > >> >> +		if (mv88e6xxx_port_is_locked(chip, chip->ports[spid].port))
> >> > >> >> +			err = mv88e6xxx_switchdev_handle_atu_miss_violation(chip,
> >> > >> >> +									    chip->ports[spid].port,
> >> > >> >> +									    &entry,
> >> > >> >> +									    fid);
> >> > >> >
> >> > >> > Do we want to suppress the ATU miss violation warnings if we're going to
> >> > >> > notify the bridge, or is it better to keep them for some reason?
> >> > >> > My logic is that they're part of normal operation, so suppressing makes
> >> > >> > sense.
> >> > >> >
> >> > >> 
> >> > >> I have been seeing many ATU member violations after the miss violation is
> >> > >> handled (using ping), and I think it could be considered to suppress the ATU member
> >> > >> violations interrupts by setting the IgnoreWrongData bit for the
> >> > >> port (sect 4.4.7). This would be something to do whenever a port is set in locked mode?
> >> > >
> >> > > So the first packet with a given MAC SA triggers an ATU miss violation
> >> > > interrupt.
> >> > >
> >> > > You program that MAC SA into the ATU with a destination port mask of all
> >> > > zeroes. This suppresses further ATU miss interrupts for this MAC SA, but
> >> > > now generates ATU member violations, because the MAC SA _is_ present in
> >> > > the ATU, but not towards the expected port (in fact, towards _no_ port).
> >> > >
> >> > > Especially if user space decides it doesn't want to authorize this MAC
> >> > > SA, it really becomes a problem because this is now a vector for denial
> >> > > of service, with every packet triggering an ATU member violation
> >> > > interrupt.
> >> > >
> >> > > So your suggestion is to set the IgnoreWrongData bit on locked ports,
> >> > > and this will suppress the actual member violation interrupts for
> >> > > traffic coming from these ports.
> >> > >
> >> > > So if the user decides to unplug a previously authorized printer from
> >> > > switch port 1 and move it to port 2, how is this handled? If there isn't
> >> > > a mechanism in place to delete the locked FDB entry when the printer
> >> > > goes away, then by setting IgnoreWrongData you're effectively also
> >> > > suppressing migration notifications.
> >> > 
> >> > I don't think such a scenario is so realistic, as changing port is not
> >> > just something done casually, besides port 2 then must also be a locked
> >> > port to have the same policy.
> >> 
> >> I think it is very realistic. It is also something which does not work
> >> is going to cause a lot of confusion. People will blame the printer,
> >> when in fact they should be blaming the switch. They will be rebooting
> >> the printer, when in fact, they need to reboot the switch etc.
> >> 
> >> I expect there is a way to cleanly support this, you just need to
> >> figure it out.
> >
> > Hans, why must port 2 also be a locked port? The FDB entry with no
> > destinations is present in the ATU, and static, why would just locked
> > ports match it?
> >
> You are right of course, but it was more from a policy standpoint as I
> pointed out. If the FDB entry is removed after some timeout and the
> device in the meantime somehow is on another port that is not locked
> with full access, the device will of course get full access.
> But since it was not given access in the first instance, the policy is
> not consistent.
> 
> >> > The other aspect is that the user space daemon that authorizes catches
> >> > the fdb add entry events and checks if it is a locked entry. So it will
> >> > be up to said daemon to decide the policy, like remove the fdb entry
> >> > after a timeout.
> >
> > When you say 'timeout', what is the moment when the timer starts counting?
> > The last reception of the user space daemon of a packet with this MAC SA,
> > or the moment when the FDB entry originally became unlocked?
> 
> I think that if the device is not given access, a timer should be
> started at that moment. No further FDB add events with the same MAC
> address will come of course until the FDB entry is removed, which I
> think would be done based on the said timer.
> >
> > I expect that once a device is authorized, and forwarding towards the
> > devices that it wants to talk to is handled in hardware, that the CPU no
> > longer receives packets from this device. In other words, are you saying
> > that you're going to break networking for the printer every 5 minutes,
> > as a keepalive measure?
> 
> No, I don't think that would be a good idea, but as we are in userspace,
> that is a policy decision of those creating the daemon. The kernel just
> facilitates, it does not make those decisions as far as I think.
> >
> > I still think there should be a functional fast path for authorized
> > station migrations.
> >
> I am not sure in what way you are suggesting that should be, if the
> kernel should actively do something there? If a station is authorized,
> and somehow is transferred to another port, if that port is not locked it
> will get access, if the port is locked a miss violation will occur etc...

Wait, if the new port is locked and the device was previously
authorized, why will the new port trigger a miss violation? This is the
part I'm not following. The authorization is still present in the form
of an ATU entry on the old locked port, is it not?

> >> > > Oh, btw, my question was: could you consider suppressing the _prints_ on
> >> > > an ATU miss violation on a locked port?
> >> > 
> >> > As there will only be such on the first packet, I think it should be
> >> > logged and those prints serve that purpose, so I think it is best to
> >> > keep the print.
> >> > If in the future some tests or other can argue for suppressing the
> >> > prints, it is an easy thing to do.
> >> 
> >> Please use a traffic generator and try to DOS one of your own
> >> switches. Can you?
> >> 
> >> 	  Andrew

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