Re: [PATCH 3/3] net: add generic MAC address derivation from machine ID

[Thorsten Scherer <T.Scherer@eckelmann.de>]

Hi Ahmad,

On Mon, Sep 11, 2023 at 05:59:27PM +0200, Ahmad Fatoum wrote:
> From: Ahmad Fatoum <ahmad@a3f.at>
> 
> Especially during development, devices often lack a MAC address. While a
> MAC address can be easily added to the environment:
> 
>   nv dev.eth0.ethaddr="aa:bb:cc:dd:ee:ff"
> 
> It's easily lost when flashing complete new images, e.g. from CI.
> Make the development experience neater by deriving a stable MAC address
> if possible.
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
>  include/net.h |  2 ++
>  net/Kconfig   | 17 +++++++++++++++++
>  net/eth.c     | 11 ++++++++++-
>  net/net.c     | 49 +++++++++++++++++++++++++++++++++++++++++++++++--
>  4 files changed, 76 insertions(+), 3 deletions(-)
> 
> diff --git a/include/net.h b/include/net.h
> index a0ef8bee0404..de43c29f74ac 100644
> --- a/include/net.h
> +++ b/include/net.h
> @@ -418,6 +418,8 @@ static inline int is_broadcast_ether_addr(const u8 *addr)
>  #define ETH_ALEN	6	/* Octets in an Ethernet address */
>  #define ETH_HLEN	14	/* Total octets in header.*/
>  
> +int generate_ether_addr(u8 *addr, int ethid);
> +
>  /**
>   * random_ether_addr - Generate software assigned random Ethernet address
>   * @addr: Pointer to a six-byte array containing the Ethernet address
> diff --git a/net/Kconfig b/net/Kconfig
> index 59f14c23cba2..04fcdcbe5bd5 100644
> --- a/net/Kconfig
> +++ b/net/Kconfig
> @@ -6,6 +6,23 @@ menuconfig NET
>  
>  if NET
>  
> +config NET_ETHADDR_FROM_MACHINE_ID
> +	bool
> +	prompt "generate stable Ethernet address"
> +	depends on MACHINE_ID && HAVE_DIGEST_SHA256 && HAVE_DIGEST_HMAC
> +	help
> +	  By default, barebox will generate random Ethernet addresses for
> +	  interfaces that had no explicit Ethernet address set via
> +	  either board code or NVMEM properties in device tree.
> +
> +	  Say y here, to randomize Ethernet addresses only if no machine ID
> +	  is available. Should barebox have a machine ID, it will be used
> +	  alonside the hostname to generate MAC addresses that are unlikely

s/alonside/alongside/

> +	  to change between subsequent runs of barebox.
> +
> +	  This is not recommended for use in production as it may leak
> +	  information about the machine ID.
> +
>  config NET_NFS
>  	bool
>  	prompt "nfs support"
> diff --git a/net/eth.c b/net/eth.c
> index ccac5e2a6488..e74c00e74a9a 100644
> --- a/net/eth.c
> +++ b/net/eth.c
> @@ -10,6 +10,7 @@
>  #include <dhcp.h>
>  #include <net.h>
>  #include <dma.h>
> +#include <machine_id.h>
>  #include <of.h>
>  #include <of_net.h>
>  #include <linux/phy.h>
> @@ -558,6 +559,7 @@ static int of_populate_ethaddr(void)
>  {
>  	char str[sizeof("xx:xx:xx:xx:xx:xx")];
>  	struct eth_device *edev;
> +	bool generated = false;
>  	int ret;
>  
>  	list_for_each_entry(edev, &netdev_list, list) {
> @@ -566,11 +568,18 @@ static int of_populate_ethaddr(void)
>  
>  		ret = of_get_mac_addr_nvmem(edev->parent->of_node,
>  					    edev->ethaddr);
> +		if (ret && IS_ENABLED(CONFIG_NET_ETHADDR_FROM_MACHINE_ID)) {
> +			ret = generate_ether_addr(edev->ethaddr, edev->dev.id);
> +			generated = true;
> +		}
>  		if (ret)
>  			continue;
>  
>  		ethaddr_to_string(edev->ethaddr, str);
> -		dev_info(&edev->dev, "Got preset MAC address from device tree: %s\n", str);
> +		if (generated)
> +			dev_notice(&edev->dev, "Generated MAC address from unique id: %s\n", str);
> +		else
> +			dev_info(&edev->dev, "Got preset MAC address from NVMEM: %s\n", str);
>  		eth_set_ethaddr(edev, edev->ethaddr);
>  	}
>  
> diff --git a/net/net.c b/net/net.c
> index bf2117ff7ec2..e38179491d7a 100644
> --- a/net/net.c
> +++ b/net/net.c
> @@ -25,6 +25,7 @@
>  #include <init.h>
>  #include <globalvar.h>
>  #include <magicvar.h>
> +#include <machine_id.h>
>  #include <linux/ctype.h>
>  #include <linux/err.h>
>  
> @@ -365,6 +366,43 @@ IPaddr_t net_get_gateway(void)
>  
>  static LIST_HEAD(connection_list);
>  
> +/**
> + * generate_ether_addr - Generates stable software assigned Ethernet address
> + * @addr: Pointer to a six-byte array to contain the Ethernet address
> + * @ethid: index of the Ethernet interface
> + *
> + * Derives an Ethernet address (MAC) from the machine ID, that's stable
> + * per board that is not multicast and has the local assigned bit set.
> + *
> + * Return 0 if an address could be generated or a negative error code otherwise.
> + */
> +int generate_ether_addr(u8 *ethaddr, int ethid)
> +{
> +	const char *hostname;
> +	uuid_t id;
> +	int ret;
> +
> +	if (!IS_ENABLED(CONFIG_NET_ETHADDR_FROM_MACHINE_ID))
> +		return -ENOSYS;
> +
> +	hostname = barebox_get_hostname();
> +	if (!hostname)
> +		return -EINVAL;
> +
> +	ret = machine_id_get_app_specific(&id, ARRAY_AND_SIZE("barebox-macaddr:"),
> +					  hostname, strlen(hostname), NULL);
> +	if (ret)
> +		return ret;
> +
> +	memcpy(ethaddr, &id.b, ETH_ALEN);
> +	eth_addr_add(ethaddr, ethid);
> +
> +	ethaddr[0] &= 0xfe;	/* clear multicast bit */
> +	ethaddr[0] |= 0x02;	/* set local assignment bit (IEEE802) */
> +
> +	return 0;
> +}
> +
>  static struct net_connection *net_new(struct eth_device *edev, IPaddr_t dest,
>  				      rx_handler_f *handler, void *ctx)
>  {
> @@ -381,9 +419,16 @@ static struct net_connection *net_new(struct eth_device *edev, IPaddr_t dest,
>  
>  	if (!is_valid_ether_addr(edev->ethaddr)) {
>  		char str[sizeof("xx:xx:xx:xx:xx:xx")];
> -		random_ether_addr(edev->ethaddr);
> +
> +		ret = generate_ether_addr(edev->ethaddr, edev->dev.id);
> +		if (ret)
> +			random_ether_addr(edev->ethaddr);
> +
>  		ethaddr_to_string(edev->ethaddr, str);
> -		dev_warn(&edev->dev, "No MAC address set. Using random address %s\n", str);
> +
> +		dev_warn(&edev->dev, "No MAC address set. Using %s %s\n",
> +			 ret == 1 ? "address computed from unique ID" : "random address",
> +			 str);
>  		eth_set_ethaddr(edev, edev->ethaddr);
>  	}
>  
> -- 
> 2.39.2
> 
> 

Regards
Thorsten