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: Sabrina Dubroca <[email-masked]>
Date: Thu, 23 Nov 2023 15:38:04 +0100

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?

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?

-- 
Sabrina