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

[Ahmad Fatoum]

From: Ahmad Fatoum <ahmad at 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 at 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
+	  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