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network: persist random eth0 MAC across boots #381

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7 changes: 7 additions & 0 deletions overlays/common/06-derived-eth0-mac/patches/01-derived-eth0-mac.patch
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Original file line number Diff line number Diff line change
@@ -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/derived-mac eth0
dhcp-up /sbin/dhcpcd
dhcp-down /sbin/dhcpcd -k
50 changes: 50 additions & 0 deletions overlays/common/06-derived-eth0-mac/root/usr/local/sbin/derived-mac
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Original file line number Diff line number Diff line change
@@ -0,0 +1,50 @@
#!/bin/bash

set -eu

is_random_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
}

ifname="${1:-}"

if [[ -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_random_mac "$current_mac"; then
echo "The $ifname MAC is not random, leaving it unchanged" >&2
exit 0
fi

serial="$(cat /oem/printer_data/.lava.sn 2>/dev/null || true)"

if [[ -z "$serial" ]]; then
serial="$(grep '^Serial[[:space:]]*:' /proc/cpuinfo 2>/dev/null | awk '{print $3}' | head -n 1)"
fi

if [[ -z "$serial" ]]; then
echo "Serial not found in /oem/printer_data/.lava.sn or /proc/cpuinfo" >&2
exit 1
fi

hash="$(printf '%s:%s\n' "$serial" "$ifname" | sha256sum | cut -d ' ' -f 1)"
stable_mac="02:${hash:0:2}:${hash:2:2}:${hash:4:2}:${hash:6:2}:${hash:8:2}"

[[ "$current_mac" == "$stable_mac" ]] || /sbin/ip link set dev "$ifname" address "$stable_mac"
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