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#!/usr/bin/env bash
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#
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# genmac - Generate a random MAC address for a Systemd-configured network interface
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#
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# Copyright (C) 2021 Pekka Helenius <pekka.helenius@fjordtek.com>
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#####################################
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trap ctrl_c INT
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function ctrl_c() {
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echo -e "\nAborting.\n"
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return
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}
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random_mac() {
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MAC=$(printf '%02x' $((0x$(od /dev/urandom -N1 -t x1 -An | cut -c 2-) & 0xFE | 0x02)); od /dev/urandom -N5 -t x1 -An | sed 's/ /:/g')
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}
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insert_mac() {
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echo -e "\nChanging MAC address information (root permission required).\n"
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sudo sed -i "/\[Link\]/!b;n;cMACAddress=$MAC" /etc/systemd/network/00-default.link
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echo -e "MAC address changed from '$MAC_OLD' to '$MAC' for interface '$MAC_DEVICE'.\n\nPlease restart this interface to apply the changes.\n\nTo restore original MAC address, either delete configuration file '/etc/systemd/network/$linkname' or set real MAC address manually into it.\n"
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return 0
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}
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geninsert_mac() {
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gennew_mac() {
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while true; do
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unset response
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read -r -p "Generate a new MAC address? [Y/n] " response
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if [[ $(echo $response | sed 's/ //g') =~ ^([yY][eE][sS]|[yY])$ ]]; then
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random_mac
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newname_mac
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else
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echo -e "\nKeeping old MAC address configuration.\n"
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return
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fi
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done
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}
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newname_mac() {
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unset response
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read -r -p "New MAC address for '$MAC_DEVICE' will be '$MAC'. Accept? [Y/n] " response
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if [[ $(echo $response | sed 's/ //g') =~ ^([yY][eE][sS]|[yY])$ ]]; then
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insert_mac
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else
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gennew_mac
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fi
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}
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newname_mac
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}
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gen_mac() {
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real_mac() {
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AVAILABLE_MACS=$(ip -br link show | sed '/LOOPBACK/d' | awk '{print NR"\t"$1"\t"$3"\t"$2}')
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IFS=$'\n'
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echo -e "\nAvailable network interfaces with their MAC addresses are:\n\n${AVAILABLE_MACS[*]}"
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echo -e "\nPlease select the interface which MAC address you want to spoof of\n"
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read -r -p "Selection [number]: " number
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if [[ ! $number =~ ^[0-9]+$ ]]; then
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echo -e "\nInvalid input value. Aborting.\n"
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return 1
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fi
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for INTERFACE in $(echo -e "${AVAILABLE_MACS[*]}"); do
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intf_num=$(echo $INTERFACE | awk '{print $1}')
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if [[ $number -eq $intf_num ]]; then
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MAC_REAL=$(echo $INTERFACE | awk '{print $3}')
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MAC_DEVICE=$(echo $INTERFACE | awk '{print $2}')
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break
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fi
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done
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unset IFS
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if [[ $MAC_REAL == "" ]]; then
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echo -e "\nNot a valid MAC address found for interface number $number. Aborting.\n"
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return 1
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fi
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}
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real_mac
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PREV_CONF=$(grep -Ril "$MAC_REAL" /etc/systemd/network/)
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if [[ ! $(echo $PREV_CONF | wc -w) -eq 0 ]]; then
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echo -e "\nUsing existing configuration file for interface '$MAC_DEVICE':\n$PREV_CONF\n"
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linkname=$(basename $PREV_CONF)
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MAC_OLD=$(awk -F= '/\[Link\]/{getline; print $2}' $PREV_CONF)
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else
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MAC_OLD=$MAC_REAL
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echo -e "\nPrevious configuration file not found. Creating it (root permission required).\n"
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read -r -p "Configuration file name? (must follow syntax: 00-default.link, 41-default.link, 98-default.link etc.): " linkname
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if [[ $linkname =~ ^[0-9][0-9]-default.link ]]; then
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if [[ ! $(sudo -n true) ]]; then
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sudo echo ""
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fi
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echo -e "[Match]\nMACAddress=$MAC_REAL\n\n[Link]\nMACAddress=$MAC_REAL\nNamePolicy=kernel database onboard slot path" \
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| sudo tee /etc/systemd/network/$linkname > /dev/null
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echo -e "Created new configuration file: /etc/systemd/network/$linkname\n"
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else
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echo -e "\nInvalid file name given. Aborting.\n"
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return 1
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fi
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fi
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unset response
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echo -e "Either randomly generated or manually specified MAC address can be used.\n"
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read -r -p "Do you want to use randomly generated MAC address? [Y/n] " response
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if [[ $(echo $response | sed 's/ //g') =~ ^([yY][eE][sS]|[yY])$ ]]; then
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random_mac
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geninsert_mac
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else
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if [[ $(echo $response | sed 's/ //g') =~ ^([nN][oO]|[nN])$ ]]; then
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read -r -p "Please type a new MAC address (Syntax is e.g. aa:bb:33:zz:f0:4a): " MAC
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maxtries=5
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while [[ $maxtries -gt 0 ]]; do
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case "$MAC" in
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[[:xdigit:]][[:xdigit:]]:[[:xdigit:]][[:xdigit:]]:[[:xdigit:]][[:xdigit:]]:[[:xdigit:]][[:xdigit:]]:[[:xdigit:]][[:xdigit:]]:[[:xdigit:]][[:xdigit:]])
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insert_mac
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;;
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esac
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unset MAC
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read -r -p "Invalid MAC address given. Please type again ($maxtries tries left): " MAC
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let maxtries--
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done
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else
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echo -e "\nInvalid answer. Aborting.\n"
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fi
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fi
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}
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echo -e "\nWARNING: Changing MAC address WILL DISRUPT connections to any network device using MAC-based authentication methods. These devices may include configured routers, WiFi hotspots etc. Remember to write down the new MAC address, and make sure you are authorized to configure the MAC address to all affected network devices if needed.\n"
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read -r -p "You are going to spoof a MAC address of a network interface of this computer. Are you sure? [Y/n] " response
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if [[ $(echo $response | sed 's/ //g') =~ ^([yY][eE][sS]|[yY])$ ]]; then
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gen_mac
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else
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echo -e "\nKeeping old MAC address configuration.\n"
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fi
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