Subject: Re: [PATCH RFC net-next v1 2/3] macsec: Detect if Rx skb is macsec-related for offloading devices that update md_dst

From: Rahul Rameshbabu <[email-masked]>
Date: Mon, 27 Nov 2023 11:10:19 -0800

On Thu, 23 Nov, 2023 15:38:04 +0100 Sabrina Dubroca <[email-masked]> wrote:
> 2023-11-16, 10:28:59 -0800, Rahul Rameshbabu wrote:
>> This detection capability will enable drivers that update md_dst to be able
>> to receive and handle both non-MACSec and MACsec traffic received and the
>> same physical port when offload is enabled.
>> 
>> This detection is not possible without device drivers that update md_dst. A
>> fallback pattern should be used for supporting such device drivers. This
>> fallback mode causes multicast messages to be cloned to both the non-macsec
>> and macsec ports, independent of whether the multicast message received was
>> encrypted over MACsec or not. Other non-macsec traffic may also fail to be
>> handled correctly for devices in promiscuous mode.
>> 
>> Link: https://lore.kernel.org/netdev/ZULRxX9eIbFiVi7v@hog/
>> Cc: Sabrina Dubroca <[email-masked]>
>> Signed-off-by: Rahul Rameshbabu <[email-masked]>
>> ---
>>  drivers/net/macsec.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
>> index 8c0b12490e89..e14f2ad2e253 100644
>> --- a/drivers/net/macsec.c
>> +++ b/drivers/net/macsec.c
>> @@ -1002,6 +1002,7 @@ static enum rx_handler_result handle_not_macsec(struct sk_buff *skb)
>>  	rcu_read_lock();
>>  	rxd = macsec_data_rcu(skb->dev);
>>  	md_dst = skb_metadata_dst(skb);
>> +	bool is_macsec_md_dst = md_dst && md_dst->type == METADATA_MACSEC;
>>  
>>  	list_for_each_entry_rcu(macsec, &rxd->secys, secys) {
>>  		struct sk_buff *nskb;
>> @@ -1014,10 +1015,13 @@ static enum rx_handler_result handle_not_macsec(struct sk_buff *skb)
>>  		if (macsec_is_offloaded(macsec) && netif_running(ndev)) {
>>  			struct macsec_rx_sc *rx_sc = NULL;
>>  
>> -			if (md_dst && md_dst->type == METADATA_MACSEC)
>> +			if (macsec->offload_md_dst && !is_macsec_md_dst)
>> +				continue;
>> +
>> +			if (is_macsec_md_dst)
>>  				rx_sc = find_rx_sc(&macsec->secy, md_dst->u.macsec_info.sci);
>>  
>> -			if (md_dst && md_dst->type == METADATA_MACSEC && !rx_sc)
>> +			if (is_macsec_md_dst && !rx_sc)
>>  				continue;
>>  
>>  			if (ether_addr_equal_64bits(hdr->h_dest,
>
> Why not skip the MAC address matching if you found the rx_sc? The way
> you're implementing it, it will still distribute broadcast received
> over the macsec port to other macsec ports on the same device, right?

That's true. Once the rx_sc is found, the skb can be diverted to the
macsec port.

>
> If the device provided md_dst, either we find the corresponding rx_sc,
> then we receive on this macsec device only, or we don't and try the
> other macsec devices.
>
> Something like this (completely untested):
>
> 	if (macsec_is_offloaded(macsec) && netif_running(ndev)) {
> 		struct macsec_rx_sc *rx_sc = NULL;
> 		bool exact = false;
>
> 		if (macsec->offload_md_dst && !is_macsec_md_dst)
> 			continue;
>
> 		if (is_macsec_md_dst) {
> 			DEBUG_NET_WARN_ON_ONCE(!macsec->offload_md_dst);
> 			rx_sc = find_rx_sc(&macsec->secy, md_dst->u.macsec_info.sci);
> 			if (!rx_sc)
> 				continue;
> 			exact = true;
> 		}
>
> 		if (exact ||
> 		    ether_addr_equal_64bits(hdr->h_dest, ndev->dev_addr)) {
> 			/* exact match, divert skb to this port */
> 	[keep the existing code after this]
>
>
> Am I missing something?

I just have one question with regards to this (will be testing this out
too). For the exact match case, if the receiving traffic was macsec
encrypted multicast, would the pkt_type be PACKET_HOST or
PACKET_BROADCAST/PACKET_MULTICAST? My intuition is screaming to me that
'[keep the existing code after this]' is not 100% true because we would
want to update the skb pkt_type to PACKET_BROADCAST/PACKET_MULTICAST
even if we are able to identify the incoming multicast frame was macsec
encrypted and specifically intended for this device. Does that sound
right?

--
Thanks,

Rahul Rameshbabu