networkd: netdev - set predictable mac address when creating netdev

src/network/networkd-netdev.c

@@ -25,6 +25,7 @@
 #include "conf-files.h"
 #include "conf-parser.h"
 #include "list.h"
+#include "siphash24.h"
 
 #define VLANID_MAX 4094
 
@@ -180,8 +181,48 @@ static int netdev_create_handler(sd_rtnl *rtnl, sd_rtnl_message *m, void *userda
         return 1;
 }
 
+#define HASH_KEY SD_ID128_MAKE(52,e1,45,bd,00,6f,29,96,21,c6,30,6d,83,71,04,48)
+
+static int netdev_get_mac(NetDev *netdev, struct ether_addr *mac) {
+        uint8_t result[8];
+        size_t l, sz;
+        uint8_t *v;
+        int r;
+
+        assert(netdev);
+        assert(netdev->name);
+        assert(mac);
+
+        l = strlen(netdev->name);
+        sz = sizeof(sd_id128_t) + l;
+        v = alloca(sz);
+
+        /* fetch some persistent data unique to the machine */
+        r = sd_id128_get_machine((sd_id128_t*) v);
+        if (r < 0)
+                return r;
+
+        /* combine with some data unique (on this machine) to this
+         * netdev */
+        memcpy(v + sizeof(sd_id128_t), netdev->name, l);
+
+        /* Let's hash the host machine ID plus the container name. We
+         * use a fixed, but originally randomly created hash key here. */
+        siphash24(result, v, sz, HASH_KEY.bytes);
+
+        assert_cc(ETH_ALEN <= sizeof(result));
+        memcpy(mac->ether_addr_octet, result, ETH_ALEN);
+
+        /* see eth_random_addr in the kernel */
+        mac->ether_addr_octet[0] &= 0xfe;        /* clear multicast bit */
+        mac->ether_addr_octet[0] |= 0x02;        /* set local assignment bit (IEEE802) */
+
+        return 0;
+}
+
 static int netdev_create(NetDev *netdev, Link *link, sd_rtnl_message_handler_t callback) {
         _cleanup_rtnl_message_unref_ sd_rtnl_message *req = NULL;
+        struct ether_addr mac;
         const char *kind;
         int r;
 
@@ -192,6 +233,12 @@ static int netdev_create(NetDev *netdev, Link *link, sd_rtnl_message_handler_t c
         assert(netdev->manager);
         assert(netdev->manager->rtnl);
 
+        r = netdev_get_mac(netdev, &mac);
+        if (r < 0) {
+                log_error("Failed to generate predictable MAC address for %s", netdev->name);
+                return r;
+        }
+
         r = sd_rtnl_message_new_link(netdev->manager->rtnl, &req, RTM_NEWLINK, 0);
         if (r < 0) {
                 log_error_netdev(netdev,
@@ -218,6 +265,14 @@ static int netdev_create(NetDev *netdev, Link *link, sd_rtnl_message_handler_t c
                 return r;
         }
 
+        r = sd_rtnl_message_append_ether_addr(req, IFLA_ADDRESS, &mac);
+        if (r < 0) {
+                log_error_netdev(netdev,
+                                 "Colud not append IFLA_ADDRESS attribute: %s",
+                                 strerror(-r));
+                return r;
+        }
+
         r = sd_rtnl_message_open_container(req, IFLA_LINKINFO);
         if (r < 0) {
                 log_error_netdev(netdev,