Overriding / Patching Linux System Serial Number

override-serial-number.sh

#!/bin/bash

# See https://schlomo.schapiro.org/2023/01/overriding-patching-linux-system-serial.html

# Copyright 2023  Forto Logistics AG & Co. KG / Schlomo Schapiro

# Permission is hereby granted, free of charge, to any person obtaining a copy of this software
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# distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the
# Software is furnished to do so, subject to the following conditions:

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# substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
# BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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set -euo pipefail

function die {
    echo -e "ERROR: $*"
    exit 1
}

for tool in bbe dmidecode; do
    type "$tool" &>/dev/null || die "cannot find $tool utility, please install"
done

function removeOverride {
    umount -v /sys/devices/virtual/dmi/id/product_serial /sys/devices/virtual/dmi/id/product_uuid /sys/firmware/dmi/tables/DMI || die "cannot remove override, please check state of /sys/devices/virtual/dmi/id/product_serial /sys/devices/virtual/dmi/id/product_uuid /sys/firmware/dmi/tables/DMI"
    rm -f /etc/fakeDMI /etc/fakeSERIAL
}

if [[ $# -eq 0 || "$1" == "--help" ]]; then
    echo "$0 < --remove | SERIAL >"
    echo "Override DMI info with given SERIAL number or remove override"
    exit 1

elif [ "$1" == "--remove" ]; then
    removeOverride
    echo "Successfully restored serial number to original >$(dmidecode -s system-serial-number)<"

elif [ -s /etc/fakeSERIAL ]; then
    die "serial number override already in place with >$(</etc/fakeSERIAL)<, please remove first"

else
    # proceed to override serial number
    new="$1"
    old="$(dmidecode -s system-serial-number)"
    if [ "$old" ]; then
        echo "Old serial: $old"
        [ ${#new} -lt ${#old} ] || die "New serial cannot be as long or longer as the old serial"
    fi

    echo "$new" >/etc/fakeSERIAL
    mount --bind /etc/fakeSERIAL /sys/devices/virtual/dmi/id/product_serial
    mount --bind /etc/fakeSERIAL /sys/devices/virtual/dmi/id/product_uuid

    bbe -e "s/$old/$new\0/" </sys/firmware/dmi/tables/DMI >/etc/fakeDMI || die "Cannot patch DMI"
    mount --bind /etc/fakeDMI /sys/firmware/dmi/tables/DMI

    check="$(dmidecode -s system-serial-number)"
    if [ "$check" == "$new" ]; then
        echo "Successfully set >$new< as new serial number."
    else
        removeOverride
        die "Overriding serial number not successful, new serial was >$check< and not >$new<."
    fi
fi