Linux Ethernet Bridging - Mar 2022 - [Bridge] [PATCH net-next 3/3] net: dsa: mv88e6xxx: mac-auth/MAB implementation

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.

Oh, btw, my question was: could you consider suppressing the _prints_ on
an ATU miss violation on a locked port?

On tor, mar 17, 2022 at 01:34, Vladimir Oltean <olteanv at gmail.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.

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.
>
> 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.