netdev - Re: [PATCH] usbnet: use each random address only once

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Date:   Wed, 29 Jun 2022 20:50:13 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Oliver Neukum <oneukum@...e.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH] usbnet: use each random address only once

On Wed, 29 Jun 2022 16:21:49 +0200 Oliver Neukum wrote:
> Even random MACs should be unique to a device.
> Get a new one each time it is used.
> 
> This bug is as old as the driver.
> 
> Signed-off-by: Oliver Neukum <oneukum@...e.com>
> ---
>  drivers/net/usb/usbnet.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
> index 02b915b1e142..a90aece93f4a 100644
> --- a/drivers/net/usb/usbnet.c
> +++ b/drivers/net/usb/usbnet.c
> @@ -1797,8 +1797,11 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
>  	}
>  
>  	/* let userspace know we have a random address */
> -	if (ether_addr_equal(net->dev_addr, node_id))
> +	if (ether_addr_equal(net->dev_addr, node_id)) {
>  		net->addr_assign_type = NET_ADDR_RANDOM;
> +		/* next device needs a new one*/
> +		eth_random_addr(node_id);
> +	}
>  
>  	if ((dev->driver_info->flags & FLAG_WLAN) != 0)
>  		SET_NETDEV_DEVTYPE(net, &wlan_type);

Why is that node_id thing even there, can we just delete it?

Leave the address as all-zero and check if driver filled it in with:

	if (!is_valid_ether_addr(net->dev_addr))
		eth_hw_addr_random(net->dev_addr);