Linux Ethernet Bridging - Oct 2022 - [Bridge] [PATCH v8 net-next 10/12] net: dsa: mv88e6xxx: mac-auth/MAB implementation

On 2022-10-21 13:22, Vladimir Oltean wrote:
> On Fri, Oct 21, 2022 at 08:47:42AM +0200, netdev at kapio-technology.com 
> wrote:
>> On 2022-10-21 00:57, Vladimir Oltean wrote:
>> > On Thu, Oct 20, 2022 at 10:20:50PM +0200, netdev at
kapio-technology.com
>> > wrote:
>> > > In general locked ports block traffic from a host based on if
there
>> > > is a
>> > > FDB entry or not. In the non-offloaded case, there is only
CPU
>> > > assisted
>> > > learning, so the normal learning mechanism has to be disabled
as any
>> > > learned entry will open the port for the learned MAC,vlan.
>> >
>> > Does it have to be that way? Why can't BR_LEARNING on a
BR_PORT_LOCKED
>> > cause the learned FDB entries to have BR_FDB_LOCKED, and
everything
>> > would be ok in that case (the port will not be opened for the
learned
>> > MAC/VLAN)?
>> 
>> I suppose you are right that basing it solely on BR_FDB_LOCKED is 
>> possible.
>> 
>> The question is then maybe if the common case where you don't need 
>> learned
>> entries for the scheme to work, e.g. with EAPOL link local packets, 
>> requires
>> less CPU load to work and is cleaner than if using BR_FDB_LOCKED 
>> entries?
> 
> I suppose the real question is what does the bridge currently do with
> BR_LEARNING + BR_PORT_LOCKED, and if that is sane and useful in any 
> case?
> It isn't a configuration that's rejected, for sure. The
configuration
> could be rejected via a bug fix patch, then in net-next it could be 
> made
> to learn these addresses with the BR_FDB_LOCKED flag.
> 
> To your question regarding the common case (no MAB): that can be 
> supported
> just fine when BR_LEARNING is off and BR_PORT_LOCKED is on, no?
> No BR_FDB_LOCKED entries will be learned.
As it is now in the bridge, the locked port part is handled before 
learning
in the ingress data path, so with BR_LEARNING and BR_PORT_LOCKED, I 
think it
will work as it does now except link local packages.

If your suggestion of BR_LEARNING causing BR_FDB_LOCKED on a locked 
port, I
guess it would be implemented under br_fdb_update() and BR_LEARNING +
BR_PORT_LOCKED would go together, forcing BR_LEARNING in this case, thus 
also
for all drivers?

On Fri, Oct 21, 2022 at 03:16:21PM +0200, netdev at kapio-technology.com
wrote:
> As it is now in the bridge, the locked port part is handled before learning
> in the ingress data path, so with BR_LEARNING and BR_PORT_LOCKED, I think
it
> will work as it does now except link local packages.
If link-local learning is enabled on a locked port, I think those
addresses should also be learned with the BR_FDB_LOCKED flag. The
creation of those locked FDB entries can be further suppressed by the
BROPT_NO_LL_LEARN flag.
> If your suggestion of BR_LEARNING causing BR_FDB_LOCKED on a locked port, I
> guess it would be implemented under br_fdb_update() and BR_LEARNING +
> BR_PORT_LOCKED would go together, forcing BR_LEARNING in this case, thus
also
> for all drivers?
Yes, basically where this is placed right now (in br_handle_frame_finish):

	if (p->flags & BR_PORT_LOCKED) {
		struct net_bridge_fdb_entry *fdb_src 			br_fdb_find_rcu(br,
eth_hdr(skb)->h_source, vid);

		if (!fdb_src) {
			unsigned long flags = 0;

			if (p->flags & BR_PORT_MAB) {
			   ~~~~~~~~~~~~~~~~~~~~~~~~
			   except check for BR_LEARNING

				__set_bit(BR_FDB_LOCKED, &flags);
				br_fdb_update(br, p, eth_hdr(skb)->h_source,
					      vid, flags);
			}
			goto drop;
		} else if (READ_ONCE(fdb_src->dst) != p ||
			   test_bit(BR_FDB_LOCAL, &fdb_src->flags) ||
			   test_bit(BR_FDB_LOCKED, &fdb_src->flags)) {
			goto drop;
		}
	}