Re: [PATCH net] macsec: Support VLAN-filtering lower devices

[Cosmin Ratiu <cratiu@nvidia.com>]

On Sat, 2026-01-10 at 23:45 +0100, Sabrina Dubroca wrote:
> 2026-01-09, 13:50:24 +0000, Cosmin Ratiu wrote:
> 
> > Would you like to see any tweaks to the proposed patch?
> 
> Well, updating the lower device's VLAN filters when not using offload
> is undesireable, so macsec_vlan_rx_{add,kill}_vid should check that
> offload is used, but then we'd have to remove/re-add then when
> offload
> is toggled after some vlan devices have been created on top of the
> macsec device.  Keeping track of all the ids we've pushed down via
> macsec_vlan_rx_add_vid seems a bit unreasonable, but maybe we can
> call vlan_{get,drop}_rx_*_filter_info when we toggle macsec offload?
> (not sure if that will have the behavior we want)
> 

Perhaps "undesirable" is too strong of a word. I would use "unneeded".
Having the encrypted VLANs in the lower dev HW filter can't do too much
harm, except maybe allowing some non-macsec packets with those vlans
when previously they wouldn't be allowed.

But remember what happened before the mentioned "Fixes" patch: the
lower device was put in promisc mode because it didn't advertise
IFF_UNICAST_FLT so it would have received all packets anyway.
So this fix is strictly better, simple enough that it can be understood
to be harmless.

The vlan_{get,drop}_rx_*_filter_info functions simply call device
notifiers when the VLAN filter flags change, they're not useful for
obtaining the list of VLANs. The upper devs keep track of those.

If I engineer the fix we're discussing here (which would make macsec
keep track of VLANs), it would be significantly more complicated, and
it belonging into net instead of net-next could be called into
question.

Cosmin.