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

From: Sabrina Dubroca <[email-masked]>
Date: Fri, 9 Jan 2026 11:26:51 +0100

2026-01-07, 12:47:23 +0200, Cosmin Ratiu wrote:
> VLAN-filtering is done through two netdev features
> (NETIF_F_HW_VLAN_CTAG_FILTER and NETIF_F_HW_VLAN_STAG_FILTER) and two
> netdev ops (ndo_vlan_rx_add_vid and ndo_vlan_rx_kill_vid).
> 
> Implement these and advertise the features if the lower device supports
> them. This allows proper VLAN filtering to work on top of macsec
> devices, when the lower device is capable of VLAN filtering.
> As a concrete example, having this chain of interfaces now works:
> vlan_filtering_capable_dev(1) -> macsec_dev(2) -> macsec_vlan_dev(3)
> 
> Before the "Fixes" commit this used to accidentally work because the
> macsec device (and thus the lower device) was put in promiscuous mode
> and the VLAN filter was not used. But after that commit correctly made
> the macsec driver expose the IFF_UNICAST_FLT flag, promiscuous mode was
> no longer used and VLAN filters on dev 1 kicked in. Without support in
> dev 2 for propagating VLAN filters down, the register_vlan_dev ->
> vlan_vid_add -> __vlan_vid_add -> vlan_add_rx_filter_info call from dev
> 3 is silently eaten (because vlan_hw_filter_capable returns false and
> vlan_add_rx_filter_info silently succeeds).

We only want to propagate VLAN filters when macsec offload is used,
no? If offload isn't used, the lower device should be unaware of
whatever is happening on top of macsec, so I don't think non-offloaded
setups are affected by this?

Even when offload is used, the lower device should probably handle
"ETH + VLAN 5" differently from "ETH + MACSEC + VLAN 5", but that may
not be possible with just the existing device ops.

-- 
Sabrina