freedombone/src/freedombone-utils-firewall

#!/bin/bash
#
# .---.                  .              .
# |                      |              |
# |--- .--. .-.  .-.  .-.|  .-. .--.--. |.-.  .-. .--.  .-.
# |    |   (.-' (.-' (   | (   )|  |  | |   )(   )|  | (.-'
# '    '     --'  --'  -' -  -' '  '   -' -'   -' '   -  --'
#
#                    Freedom in the Cloud
#
# Firewall functions
#
# TODO: in future investigate using nftables
#
# License
# =======
#
# Copyright (C) 2014-2016 Bob Mottram <bob@freedombone.net>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

FIREWALL_CONFIG=$HOME/${PROJECT_NAME}-firewall.cfg
FIREWALL_DOMAINS=$HOME/${PROJECT_NAME}-firewall-domains.cfg

function save_firewall_settings {
    iptables-save > /etc/firewall.conf
    ip6tables-save > /etc/firewall6.conf
    printf '#!/bin/sh\n' > /etc/network/if-up.d/iptables
    printf 'iptables-restore < /etc/firewall.conf\n' >> /etc/network/if-up.d/iptables
    printf 'ip6tables-restore < /etc/firewall6.conf\n' >> /etc/network/if-up.d/iptables
    if [ -f /etc/network/if-up.d/iptables ]; then
        chmod +x /etc/network/if-up.d/iptables
    fi
}

function firewall_block_bad_ip_ranges {
    if [ $INSTALLING_MESH ]; then
        return
    fi
    if [[ $(is_completed $FUNCNAME) == "1" ]]; then
        return
    fi

    # There are various blocklists out there, but they're difficult
    # to verify. Indiscriminately blocking ranges without evidence
    # would be a bad idea.

    # From Wikipedia and elsewhere: US military addresses
    iptables -A INPUT -s 6.0.0.0/8 -j DROP
    iptables -A OUTPUT -s 6.0.0.0/8 -j DROP
    iptables -A INPUT -s 7.0.0.0/8 -j DROP
    iptables -A OUTPUT -s 7.0.0.0/8 -j DROP
    iptables -A INPUT -s 11.0.0.0/8 -j DROP
    iptables -A OUTPUT -s 11.0.0.0/8 -j DROP
    iptables -A INPUT -s 21.0.0.0/8 -j DROP
    iptables -A OUTPUT -s 21.0.0.0/8 -j DROP
    iptables -A INPUT -s 22.0.0.0/8 -j DROP
    iptables -A OUTPUT -s 22.0.0.0/8 -j DROP
    iptables -A INPUT -s 26.0.0.0/8 -j DROP
    iptables -A OUTPUT -s 26.0.0.0/8 -j DROP
    iptables -A INPUT -s 28.0.0.0/8 -j DROP
    iptables -A OUTPUT -s 28.0.0.0/8 -j DROP
    iptables -A INPUT -s 29.0.0.0/8 -j DROP
    iptables -A OUTPUT -s 29.0.0.0/8 -j DROP
    iptables -A INPUT -s 30.0.0.0/8 -j DROP
    iptables -A OUTPUT -s 30.0.0.0/8 -j DROP
    iptables -A INPUT -s 33.0.0.0/8 -j DROP
    iptables -A OUTPUT -s 33.0.0.0/8 -j DROP
    iptables -A INPUT -s 55.0.0.0/8 -j DROP
    iptables -A OUTPUT -s 55.0.0.0/8 -j DROP
    iptables -A INPUT -s 214.0.0.0/8 -j DROP
    iptables -A OUTPUT -s 214.0.0.0/8 -j DROP
    iptables -A INPUT -s 215.0.0.0/8 -j DROP
    iptables -A OUTPUT -s 215.0.0.0/8 -j DROP
    save_firewall_settings
    mark_completed $FUNCNAME
}

function global_rate_limit {
    if ! grep -q "tcp_challenge_ack_limit" /etc/sysctl.conf; then
        echo 'net.ipv4.tcp_challenge_ack_limit = 999999999' >> /etc/sysctl.conf
    else
        sed -i 's|net.ipv4.tcp_challenge_ack_limit.*|net.ipv4.tcp_challenge_ack_limit = 999999999|g' /etc/sysctl.conf
    fi
    sysctl -p -q
}

function enable_ipv6 {
    # endure that ipv6 is enabled and can route
    sed -i 's/net.ipv6.conf.all.disable_ipv6.*/net.ipv6.conf.all.disable_ipv6 = 0/g' /etc/sysctl.conf
    #sed -i "s/net.ipv6.conf.all.accept_redirects.*/net.ipv6.conf.all.accept_redirects = 1/g" /etc/sysctl.conf
    #sed -i "s/net.ipv6.conf.all.accept_source_route.*/net.ipv6.conf.all.accept_source_route = 1/g" /etc/sysctl.conf
    sed -i "s/net.ipv6.conf.all.forwarding.*/net.ipv6.conf.all.forwarding=1/g" /etc/sysctl.conf
    echo 1 > /proc/sys/net/ipv6/conf/all/forwarding
}

function configure_firewall {
    if [ $INSTALLING_MESH ]; then
        mesh_firewall
        return
    fi
    if grep -q "RELATED" /etc/firewall.conf; then
        # recreate the firewall to remove RELATED
        sed -i "/firewall/d" $COMPLETION_FILE
    fi
    if [[ $(is_completed $FUNCNAME) == "1" ]]; then
        return
    fi
    if [[ $INSTALLED_WITHIN_DOCKER == "yes" ]]; then
        # docker does its own firewalling
        return
    fi
    iptables -P INPUT ACCEPT
    ip6tables -P INPUT ACCEPT
    iptables -F
    ip6tables -F
    iptables -t nat -F
    ip6tables -t nat -F
    iptables -X
    ip6tables -X
    iptables -P INPUT DROP
    ip6tables -P INPUT DROP
    iptables -P FORWARD DROP
    ip6tables -P FORWARD DROP
    iptables -A INPUT -i lo -j ACCEPT
    iptables -A INPUT -m conntrack --ctstate ESTABLISHED -j ACCEPT

    # Make sure incoming tcp connections are SYN packets
    iptables -A INPUT -p tcp ! --syn -m state --state NEW -j DROP

    # Drop packets with incoming fragments
    iptables -A INPUT -f -j DROP

    # Drop bogons
    iptables -A INPUT -p tcp --tcp-flags ALL ALL -j DROP
    iptables -A INPUT -p tcp --tcp-flags ALL FIN,PSH,URG -j DROP
    iptables -A INPUT -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j DROP

    # Incoming malformed NULL packets:
    iptables -A INPUT -p tcp --tcp-flags ALL NONE -j DROP

    mark_completed $FUNCNAME
}

function firewall_drop_telnet {
    if [[ $(is_completed $FUNCNAME) == "1" ]]; then
        return
    fi
    # telnet isn't enabled as an input and we can also
    # drop any outgoing telnet, just in case
    iptables -A OUTPUT -p tcp --dport telnet -j REJECT
    iptables -A OUTPUT -p udp --dport telnet -j REJECT
    function_check save_firewall_settings
    save_firewall_settings
    mark_completed $FUNCNAME
}

function configure_firewall_ping {
    if [[ $(is_completed $FUNCNAME) == "1" ]]; then
        return
    fi
    # Only allow ping for mesh installs
    if [[ $SYSTEM_TYPE != "mesh"* ]]; then
        return
    fi
    iptables -A INPUT -p icmp --icmp-type echo-request -j ACCEPT
    iptables -A OUTPUT -p icmp --icmp-type echo-reply -j ACCEPT
    function_check save_firewall_settings
    save_firewall_settings
    mark_completed $FUNCNAME
}

function configure_internet_protocol {
    if [[ $(is_completed $FUNCNAME) == "1" ]]; then
        return
    fi
    if [[ $SYSTEM_TYPE == "mesh"* ]]; then
        return
    fi

    sed -i "s/#net.ipv4.tcp_syncookies.*/net.ipv4.tcp_syncookies=1/g" /etc/sysctl.conf
    sed -i "s/#net.ipv4.conf.all.accept_redirects.*/net.ipv4.conf.all.accept_redirects = 0/g" /etc/sysctl.conf
    sed -i "s/#net.ipv6.conf.all.accept_redirects.*/net.ipv6.conf.all.accept_redirects = 0/g" /etc/sysctl.conf
    sed -i "s/#net.ipv4.conf.all.send_redirects.*/net.ipv4.conf.all.send_redirects = 0/g" /etc/sysctl.conf
    sed -i "s/#net.ipv4.conf.all.accept_source_route.*/net.ipv4.conf.all.accept_source_route = 0/g" /etc/sysctl.conf
    sed -i "s/#net.ipv6.conf.all.accept_source_route.*/net.ipv6.conf.all.accept_source_route = 0/g" /etc/sysctl.conf
    sed -i "s/#net.ipv4.conf.default.rp_filter.*/net.ipv4.conf.default.rp_filter=1/g" /etc/sysctl.conf
    sed -i "s/#net.ipv4.conf.all.rp_filter.*/net.ipv4.conf.all.rp_filter=1/g" /etc/sysctl.conf
    sed -i "s/#net.ipv4.ip_forward.*/net.ipv4.ip_forward=0/g" /etc/sysctl.conf
    sed -i "s/#net.ipv6.conf.all.forwarding.*/net.ipv6.conf.all.forwarding=0/g" /etc/sysctl.conf

    sed -i "s/# net.ipv4.tcp_syncookies.*/net.ipv4.tcp_syncookies=1/g" /etc/sysctl.conf
    sed -i "s/# net.ipv4.conf.all.accept_redirects.*/net.ipv4.conf.all.accept_redirects = 0/g" /etc/sysctl.conf
    sed -i "s/# net.ipv6.conf.all.accept_redirects.*/net.ipv6.conf.all.accept_redirects = 0/g" /etc/sysctl.conf
    sed -i "s/# net.ipv4.conf.all.send_redirects.*/net.ipv4.conf.all.send_redirects = 0/g" /etc/sysctl.conf
    sed -i "s/# net.ipv4.conf.all.accept_source_route.*/net.ipv4.conf.all.accept_source_route = 0/g" /etc/sysctl.conf
    sed -i "s/# net.ipv6.conf.all.accept_source_route.*/net.ipv6.conf.all.accept_source_route = 0/g" /etc/sysctl.conf
    sed -i "s/# net.ipv4.conf.default.rp_filter.*/net.ipv4.conf.default.rp_filter=1/g" /etc/sysctl.conf
    sed -i "s/# net.ipv4.conf.all.rp_filter.*/net.ipv4.conf.all.rp_filter=1/g" /etc/sysctl.conf
    sed -i "s/# net.ipv4.ip_forward.*/net.ipv4.ip_forward=0/g" /etc/sysctl.conf
    sed -i "s/# net.ipv6.conf.all.forwarding.*/net.ipv6.conf.all.forwarding=0/g" /etc/sysctl.conf


    if ! grep -q "ignore pings" /etc/sysctl.conf; then
        echo '# ignore pings' >> /etc/sysctl.conf
        echo 'net.ipv4.icmp_echo_ignore_all = 1' >> /etc/sysctl.conf
        echo 'net.ipv6.icmp_echo_ignore_all = 1' >> /etc/sysctl.conf
    fi
    if ! grep -q "disable ipv6" /etc/sysctl.conf; then
        echo '# disable ipv6' >> /etc/sysctl.conf
        echo 'net.ipv6.conf.all.disable_ipv6 = 1' >> /etc/sysctl.conf
    fi
    if ! grep -q "net.ipv4.tcp_synack_retries" /etc/sysctl.conf; then
        echo 'net.ipv4.tcp_synack_retries = 2' >> /etc/sysctl.conf
        echo 'net.ipv4.tcp_syn_retries = 1' >> /etc/sysctl.conf
    fi
    if ! grep -q "keepalive" /etc/sysctl.conf; then
        echo '# keepalive' >> /etc/sysctl.conf
        echo 'net.ipv4.tcp_keepalive_probes = 9' >> /etc/sysctl.conf
        echo 'net.ipv4.tcp_keepalive_intvl = 75' >> /etc/sysctl.conf
        echo 'net.ipv4.tcp_keepalive_time = 7200' >> /etc/sysctl.conf
    fi
    if ! grep -q "net.ipv4.conf.default.send_redirects" /etc/sysctl.conf; then
        echo "net.ipv4.conf.default.send_redirects = 0" >> /etc/sysctl.conf
    else
        sed -i "s|# net.ipv4.conf.default.send_redirects.*|net.ipv4.conf.default.send_redirects = 0|g" /etc/sysctl.conf
        sed -i "s|#net.ipv4.conf.default.send_redirects.*|net.ipv4.conf.default.send_redirects = 0|g" /etc/sysctl.conf
        sed -i "s|net.ipv4.conf.default.send_redirects.*|net.ipv4.conf.default.send_redirects = 0|g" /etc/sysctl.conf
    fi
    if ! grep -q "net.ipv4.conf.all.secure_redirects" /etc/sysctl.conf; then
        echo "net.ipv4.conf.all.secure_redirects = 0" >> /etc/sysctl.conf
    else
        sed -i "s|# net.ipv4.conf.all.secure_redirects.*|net.ipv4.conf.all.secure_redirects = 0|g" /etc/sysctl.conf
        sed -i "s|#net.ipv4.conf.all.secure_redirects.*|net.ipv4.conf.all.secure_redirects = 0|g" /etc/sysctl.conf
        sed -i "s|net.ipv4.conf.all.secure_redirects.*|net.ipv4.conf.all.secure_redirects = 0|g" /etc/sysctl.conf
    fi
    if ! grep -q "net.ipv4.conf.default.accept_source_route" /etc/sysctl.conf; then
        echo "net.ipv4.conf.default.accept_source_route = 0" >> /etc/sysctl.conf
    else
        sed -i "s|# net.ipv4.conf.default.accept_source_route.*|net.ipv4.conf.default.accept_source_route = 0|g" /etc/sysctl.conf
        sed -i "s|#net.ipv4.conf.default.accept_source_route.*|net.ipv4.conf.default.accept_source_route = 0|g" /etc/sysctl.conf
        sed -i "s|net.ipv4.conf.default.accept_source_route.*|net.ipv4.conf.default.accept_source_route = 0|g" /etc/sysctl.conf
    fi
    if ! grep -q "net.ipv4.conf.default.secure_redirects" /etc/sysctl.conf; then
        echo "net.ipv4.conf.default.secure_redirects = 0" >> /etc/sysctl.conf
    else
        sed -i "s|# net.ipv4.conf.default.secure_redirects.*|net.ipv4.conf.default.secure_redirects = 0|g" /etc/sysctl.conf
        sed -i "s|#net.ipv4.conf.default.secure_redirects.*|net.ipv4.conf.default.secure_redirects = 0|g" /etc/sysctl.conf
        sed -i "s|net.ipv4.conf.default.secure_redirects.*|net.ipv4.conf.default.secure_redirects = 0|g" /etc/sysctl.conf
    fi
    if ! grep -q "net.ipv4.conf.default.accept_redirects" /etc/sysctl.conf; then
        echo "net.ipv4.conf.default.accept_redirects = 0" >> /etc/sysctl.conf
    else
        sed -i "s|# net.ipv4.conf.default.accept_redirects.*|net.ipv4.conf.default.accept_redirects = 0|g" /etc/sysctl.conf
        sed -i "s|#net.ipv4.conf.default.accept_redirects.*|net.ipv4.conf.default.accept_redirects = 0|g" /etc/sysctl.conf
        sed -i "s|net.ipv4.conf.default.accept_redirects.*|net.ipv4.conf.default.accept_redirects = 0|g" /etc/sysctl.conf
    fi
    mark_completed $FUNCNAME
}

function mesh_firewall {
    FIREWALL_FILENAME=${rootdir}/etc/systemd/system/meshfirewall.service
    MESH_FIREWALL_SCRIPT=${rootdir}/usr/bin/mesh-firewall

    echo '#!/bin/bash' > $MESH_FIREWALL_SCRIPT
    echo 'iptables -P INPUT ACCEPT' >> $MESH_FIREWALL_SCRIPT
    echo 'ip6tables -P INPUT ACCEPT' >> $MESH_FIREWALL_SCRIPT
    echo 'iptables -F' >> $MESH_FIREWALL_SCRIPT
    echo 'ip6tables -F' >> $MESH_FIREWALL_SCRIPT
    echo 'iptables -t nat -F' >> $MESH_FIREWALL_SCRIPT
    echo 'ip6tables -t nat -F' >> $MESH_FIREWALL_SCRIPT
    echo 'iptables -X' >> $MESH_FIREWALL_SCRIPT
    echo 'ip6tables -X' >> $MESH_FIREWALL_SCRIPT
    echo 'iptables -P INPUT DROP' >> $MESH_FIREWALL_SCRIPT
    echo 'ip6tables -P INPUT DROP' >> $MESH_FIREWALL_SCRIPT
    echo 'iptables -A INPUT -i lo -j ACCEPT' >> $MESH_FIREWALL_SCRIPT
    echo 'iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT' >> $MESH_FIREWALL_SCRIPT
    echo '' >> $MESH_FIREWALL_SCRIPT
    echo '# Make sure incoming tcp connections are SYN packets' >> $MESH_FIREWALL_SCRIPT
    echo 'iptables -A INPUT -p tcp ! --syn -m state --state NEW -j DROP' >> $MESH_FIREWALL_SCRIPT
    echo '' >> $MESH_FIREWALL_SCRIPT
    echo '# Drop packets with incoming fragments' >> $MESH_FIREWALL_SCRIPT
    echo 'iptables -A INPUT -f -j DROP' >> $MESH_FIREWALL_SCRIPT
    echo '' >> $MESH_FIREWALL_SCRIPT
    echo '# Drop bogons' >> $MESH_FIREWALL_SCRIPT
    echo 'iptables -A INPUT -p tcp --tcp-flags ALL ALL -j DROP' >> $MESH_FIREWALL_SCRIPT
    echo 'iptables -A INPUT -p tcp --tcp-flags ALL FIN,PSH,URG -j DROP' >> $MESH_FIREWALL_SCRIPT
    echo 'iptables -A INPUT -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j DROP' >> $MESH_FIREWALL_SCRIPT
    echo '' >> $MESH_FIREWALL_SCRIPT
    echo '# Incoming malformed NULL packets:' >> $MESH_FIREWALL_SCRIPT
    echo 'iptables -A INPUT -p tcp --tcp-flags ALL NONE -j DROP' >> $MESH_FIREWALL_SCRIPT
    echo '' >> $MESH_FIREWALL_SCRIPT
    echo "iptables -A INPUT -p tcp --dport $TOX_PORT -j ACCEPT" >> $MESH_FIREWALL_SCRIPT
    echo "iptables -A INPUT -i $WIFI_INTERFACE -p udp --dport $ZERONET_PORT -j ACCEPT" >> $MESH_FIREWALL_SCRIPT
    echo "iptables -A INPUT -i $WIFI_INTERFACE -p tcp --dport $ZERONET_PORT -j ACCEPT" >> $MESH_FIREWALL_SCRIPT
    echo "iptables -A INPUT -i $WIFI_INTERFACE -p udp --dport $TRACKER_PORT -j ACCEPT" >> $MESH_FIREWALL_SCRIPT
    echo "iptables -A INPUT -i $WIFI_INTERFACE -p tcp --dport $TRACKER_PORT -j ACCEPT" >> $MESH_FIREWALL_SCRIPT
    echo "iptables -A INPUT -i $WIFI_INTERFACE -p udp --dport 1900 -j ACCEPT" >> $MESH_FIREWALL_SCRIPT
    chmod +x $MESH_FIREWALL_SCRIPT

    echo '[Unit]' > $FIREWALL_FILENAME
    echo 'Description=Mesh Firewall' >> $FIREWALL_FILENAME
    echo '' >> $FIREWALL_FILENAME
    echo '[Service]' >> $FIREWALL_FILENAME
    echo 'Type=oneshot' >> $FIREWALL_FILENAME
    echo 'ExecStart=/usr/bin/mesh-firewall' >> $FIREWALL_FILENAME
    echo 'RemainAfterExit=no' >> $FIREWALL_FILENAME
    echo '' >> $FIREWALL_FILENAME
    echo 'TimeoutSec=30' >> $FIREWALL_FILENAME
    echo '' >> $FIREWALL_FILENAME
    echo '[Install]' >> $FIREWALL_FILENAME
    echo 'WantedBy=multi-user.target' >> $FIREWALL_FILENAME
    chmod +x $FIREWALL_FILENAME
    chroot "$rootdir" systemctl enable meshfirewall
}

function firewall_add {
    firewall_name=$(echo "$1" | sed "s| |-|g")
    firewall_port=$2
    firewall_protocol="$3"

    if ! grep -q "${firewall_name}=${firewall_port}" $FIREWALL_CONFIG; then
        echo "${firewall_name}=${firewall_port}" >> $FIREWALL_CONFIG
        if [ ! ${firewall_protocol} ]; then
            iptables -A INPUT -p udp --dport ${firewall_port} -j ACCEPT
            iptables -A INPUT -p tcp --dport ${firewall_port} -j ACCEPT
        else
            if [[ "${firewall_protocol}" == *"udp"* ]]; then
                iptables -A INPUT -p udp --dport ${firewall_port} -j ACCEPT
            fi
            if [[ "${firewall_protocol}" == *"tcp"* ]]; then
                iptables -A INPUT -p tcp --dport ${firewall_port} -j ACCEPT
            fi
        fi
        save_firewall_settings
    fi
}

function firewall_add_range {
    firewall_name=$(echo "$1" | sed "s| |-|g")
    firewall_port_start=$2
    firewall_port_end=$3
    firewall_protocol="$4"

    if ! grep -q "${firewall_name}=${firewall_port_start}:${firewall_port_end}" $FIREWALL_CONFIG; then
        echo "${firewall_name}=${firewall_port_start}:${firewall_port_end}" >> $FIREWALL_CONFIG
        if [ ! ${firewall_protocol} ]; then
            iptables -A INPUT -p udp --dport ${firewall_port_start}:${firewall_port_end} -j ACCEPT
            iptables -A INPUT -p tcp --dport ${firewall_port_start}:${firewall_port_end} -j ACCEPT
        else
            if [[ "${firewall_protocol}" == *"udp"* ]]; then
                iptables -A INPUT -p udp --dport ${firewall_port_start}:${firewall_port_end} -j ACCEPT
            fi
            if [[ "${firewall_protocol}" == *"tcp"* ]]; then
                iptables -A INPUT -p tcp --dport ${firewall_port_start}:${firewall_port_end} -j ACCEPT
            fi
        fi
        save_firewall_settings
    fi
}


function firewall_remove {
    firewall_port=$1
    firewall_protocol="$2"

    if [ ! -f $FIREWALL_CONFIG ]; then
        return
    fi

    if grep -q "=${firewall_port}" $FIREWALL_CONFIG; then
        if [ ! ${firewall_protocol} ]; then
            iptables -D INPUT -p udp --dport ${firewall_port} -j ACCEPT
            iptables -D INPUT -p tcp --dport ${firewall_port} -j ACCEPT
        else
            if [[ "${firewall_protocol}" == *"udp"* ]]; then
                iptables -D INPUT -p udp --dport ${firewall_port} -j ACCEPT
            fi
            if [[ "${firewall_protocol}" == *"tcp"* ]]; then
                iptables -D INPUT -p tcp --dport ${firewall_port} -j ACCEPT
            fi
        fi
        sed -i "/=${firewall_port}/d" $FIREWALL_CONFIG
        save_firewall_settings
    fi
}

function domain_to_hex_string {
    domain="$1"
    ctr=1
    segment=$(echo "$domain" | awk -F '.' -v value="$ctr" '{print $value}')
    while [ ${#segment} -gt 0 ]
    do
        characters=$(echo -n "$segment" | wc -c)
        hexnum=$(echo "obase=16; $characters" | bc)
        echo -n "|"
        if [ $(echo -n "$hexnum" | wc -c) -lt 2 ]; then
            echo -n "0"
        fi
        echo -n "$hexnum|$segment"
        ctr=$((ctr + 1))
        segment=$(echo "$domain" | awk -F '.' -v value="$ctr" '{print $value}')
    done
    echo ""
}

function firewall_block_domain {
    blocked_domain="$1"
    if ! grep "$blocked_domain" $FIREWALL_DOMAINS; then
        hexstr=$(domain_to_hex_string $blocked_domain)
        iptables -A INPUT -p udp --dport 53 -m string --hex-string "$hexstr" --algo bm -j DROP
        iptables -A INPUT -p tcp --dport 53 -m string --hex-string "$hexstr" --algo bm -j DROP
        iptables -A OUTPUT -p udp --dport 53 -m string --hex-string "$hexstr" --algo bm -j DROP
        iptables -A OUTPUT -p tcp --dport 53 -m string --hex-string "$hexstr" --algo bm -j DROP
        iptables -I FORWARD -p udp --dport 53 -m string --hex-string "$hexstr" --algo bm -j DROP
        iptables -I FORWARD -p tcp --dport 53 -m string --hex-string "$hexstr" --algo bm -j DROP
        echo "${blocked_domain}" >> $FIREWALL_DOMAINS
        save_firewall_settings
    fi
}

function firewall_unblock_domain {
    unblocked_domain="$1"
    if grep "${unblocked_domain}" $FIREWALL_DOMAINS; then
        hexstr=$(domain_to_hex_string $unblocked_domain)
        iptables -D INPUT -p udp --dport 53 -m string --hex-string "$hexstr" --algo bm -j DROP
        iptables -D INPUT -p tcp --dport 53 -m string --hex-string "$hexstr" --algo bm -j DROP
        iptables -D OUTPUT -p udp --dport 53 -m string --hex-string "$hexstr" --algo bm -j DROP
        iptables -D OUTPUT -p tcp --dport 53 -m string --hex-string "$hexstr" --algo bm -j DROP
        iptables -D FORWARD -p udp --dport 53 -m string --hex-string "$hexstr" --algo bm -j DROP
        iptables -D FORWARD -p tcp --dport 53 -m string --hex-string "$hexstr" --algo bm -j DROP
        sed -i "/${unblocked_domain}/d" $FIREWALL_DOMAINS
        save_firewall_settings
    fi
}

# NOTE: deliberately no exit 0