Use persisted random MACs for eth0 interface (#410)

paxx12 · web-flow · commit 24054e5665c9 · 2026-04-21T19:52:05.000+09:00
Add a persistent MAC pre-up hook for eth0 and implement
/usr/local/sbin/derived-mac to generate interface MAC
for locally administered mac address.

This will be used for cases where there's no mac address configured
on USB adapter, due to missing firmware of other reasons.
diff --git a/overlays/common/06-restore-eth0-mac/patches/01-restore-eth0-mac.patch b/overlays/common/06-restore-eth0-mac/patches/01-restore-eth0-mac.patch
@@ -0,0 +1,7 @@
+--- a/etc/network/interfaces.d/eth0
++++ b/etc/network/interfaces.d/eth0
+@@ -1,3 +1,4 @@
+ iface eth0 inet manual
++	pre-up /usr/local/sbin/restore-mac eth0
+ 	dhcp-up /sbin/dhcpcd
+ 	dhcp-down /sbin/dhcpcd -k
diff --git a/overlays/common/06-restore-eth0-mac/root/usr/local/sbin/restore-mac b/overlays/common/06-restore-eth0-mac/root/usr/local/sbin/restore-mac
@@ -0,0 +1,63 @@
+#!/bin/bash
+
+set -eu
+
+is_locally_administered_unicast_mac() {
+  case "$1" in
+    [0-9a-fA-F][0-9a-fA-F]:*)
+      first_octet="${1%%:*}"
+      first_octet_value=$((0x$first_octet))
+      [[ $((first_octet_value & 0x02)) -ne 0 ]] && [[ $((first_octet_value & 0x01)) -eq 0 ]]
+      ;;
+    *)
+      return 1
+      ;;
+  esac
+}
+
+is_valid_mac_address() {
+  [[ "$1" =~ ^([0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}$ ]]
+}
+
+generate_random_mac() {
+  local raw
+
+  raw="$(hexdump -n 5 -v -e '/1 "%02x"' /dev/urandom)"
+
+  printf 'fe:%s:%s:%s:%s:%s\n' \
+    "${raw:0:2}" \
+    "${raw:2:2}" \
+    "${raw:4:2}" \
+    "${raw:6:2}" \
+    "${raw:8:2}"
+}
+
+ifname="${1:-}"
+
+if [[ $# -ne 1 || -z "$ifname" ]]; then
+  echo "Usage: $0 <ifname>" >&2
+  exit 1
+fi
+
+if [[ ! -e "/sys/class/net/$ifname/address" ]]; then
+  echo "Interface '$ifname' does not exist" >&2
+  exit 1
+fi
+
+current_mac="$(cat "/sys/class/net/$ifname/address" 2>/dev/null || true)"
+if ! is_locally_administered_unicast_mac "$current_mac"; then
+  echo "The $ifname MAC is not random, leaving it unchanged" >&2
+  exit 0
+fi
+
+mac_dir="/oem/printer_data/network"
+mac_file="$mac_dir/${ifname}.address"
+mkdir -p "$mac_dir"
+
+stable_mac="$(cat "$mac_file" 2>/dev/null || true)"
+if ! is_valid_mac_address "$stable_mac"; then
+  stable_mac="$(generate_random_mac)"
+  printf '%s\n' "$stable_mac" > "$mac_file"
+fi
+
+[[ "$current_mac" == "$stable_mac" ]] || /sbin/ip link set dev "$ifname" address "$stable_mac"
