Subject: Re: [PATCH net-next 2/3] macsec: Detect if Rx skb is macsec-related for offloading devices that update md_dst

From: Rahul Rameshbabu <[email-masked]>
Date: Fri, 19 Apr 2024 11:01:20 -0700

On Fri, 19 Apr, 2024 17:05:52 +0200 Sabrina Dubroca <[email-masked]> wrote:
> 2024-04-18, 18:17:16 -0700, Rahul Rameshbabu wrote:
<snip>
>> +			/* This datapath is insecure because it is unable to
>> +			 * enforce isolation of broadcast/multicast traffic and
>> +			 * unicast traffic with promiscuous mode on the macsec
>> +			 * netdev. Since the core stack has no mechanism to
>> +			 * check that the hardware did indeed receive MACsec
>> +			 * traffic, it is possible that the response handling
>> +			 * done by the MACsec port was to a plaintext packet.
>> +			 * This violates the MACsec protocol standard.
>> +			 */
>> +			DEBUG_NET_WARN_ON_ONCE(true);
>
> If you insist on this warning (and I'm not convinced it's useful,
> since if the HW is already built and cannot inform the driver, there's
> nothing the driver implementer can do), I would move it somewhere into
> the config path. macsec_update_offload would be a better location for
> this kind of warning (maybe with a pr_warn (not limited to debug
> configs) saying something like "MACsec offload on devices that don't
> support md_dst are insecure: they do not provide proper isolation of
> traffic"). The comment can stay here.
>

I do not like the warning either. I left it mainly if it needed further
discussion on the mailing list. Will remove it in my next revision. That
said, it may make sense to advertise rx_uses_md_dst over netlink to
annotate what macsec offload path a device uses? Just throwing out an
idea here.

>>  			if (ether_addr_equal_64bits(hdr->h_dest,
>>  						    ndev->dev_addr)) {
>>  				/* exact match, divert skb to this port */

--
Thanks,

Rahul Rameshbabu