Message-ID: <20220317172013.rhjvknre5w7mfmlo@skbuf>
Date:   Thu, 17 Mar 2022 19:20:13 +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 05:58:26PM +0100, Hans Schultz wrote:
> On tor, mar 17, 2022 at 18:18, Vladimir Oltean <olteanv@...il.com> wrote:
> > 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?
> >
> I am sure (have not tested) that a miss violation will occur. It might
> be a member violation in this instance though.
> When thinking of it, afaik there is no way today of having fine control
> over the DPV when adding a FDB entry.
> If the DPV could be finer controlled the entry could cover several
> possible ports and the fast (immediate migration) will be accomplished?

I'm not sure I understand this, either.

You're saying we should configure the authorizations as de-facto
multicast ATU entries towards all locked ports, so that there wouldn't
be any violation when a station migrates, because the new port is still
in the destination port mask of the ATU entry?

Yes, but... this leaks traffic between ports to a significant degree.
Any packet that targets your printer now targets your colleague's printer too.

I was expecting you'd say that when the cable is unplugged from the
switch, the authorization daemon is notified through rtnetlink of the
link state change, and it flushes the port of addresses it has added
(because the kernel surely does not do this).

This could work to an extent, but it wouldn't handle the case where the
printer isn't connected directly to the 802.1X port, but through
another dumb switch. I don't know enough about 802.1X, but I don't see
why this isn't a valid configuration.

To explain what I'm thinking of. At office, IT gave one Ethernet port to
each desk, but I have multiple devices. I have a PC, a printer, and a
development board, each with a single Ethernet port, so I use a dumb
4-port switch to connect all these devices to the 802.1X port beneath my
desk. I talked to IT, brought my printer to them, they agreed to bypass
802.1X authorization for it based on the MAC address on its label.

I've been working from home for the past few years, but now I need to
return to office. But since years have passed, some colleagues left,
some new colleagues came, and I need to change my desk. The new one
belonged to a co-worker who also had a dumb switch on his desk, so I see
no reason to move mine too. I unplug the printer from my dumb switch,
plug it into the new one, but it doesn't work. What do I do, open a
ticket to IT asking for halp?

To be honest this is purely fictional and I haven't tried it, but it
sounds like I should when I get the chance, to get a better image of how
things are supposed to work.

> >> >> > > 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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