#!/bin/sh
#
# Script for automatic setup of an IPsec VPN server on Amazon Linux 2
# Works on any dedicated server or virtual private server (VPS)
#
# DO NOT RUN THIS SCRIPT ON YOUR PC OR MAC!
#
# The latest version of this script is available at:
# https://github.com/hwdsl2/setup-ipsec-vpn
#
# Copyright (C) 2020-2021 Lin Song <linsongui@gmail.com>
#
# This work is licensed under the Creative Commons Attribution-ShareAlike 3.0
# Unported License: http://creativecommons.org/licenses/by-sa/3.0/
#
# Attribution required: please include my name in any derivative and let me
# know how you have improved it!

# =====================================================

# Define your own values for these variables
# - IPsec pre-shared key, VPN username and password
# - All values MUST be placed inside 'single quotes'
# - DO NOT use these special characters within values: \ " '

YOUR_IPSEC_PSK=''
YOUR_USERNAME=''
YOUR_PASSWORD=''

# Important notes:   https://git.io/vpnnotes
# Setup VPN clients: https://git.io/vpnclients
# IKEv2 guide:       https://git.io/ikev2

# =====================================================

export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
SYS_DT=$(date +%F-%T | tr ':' '_')

exiterr()  { echo "Error: $1" >&2; exit 1; }
exiterr2() { exiterr "'yum install' failed."; }
conf_bk() { /bin/cp -f "$1" "$1.old-$SYS_DT" 2>/dev/null; }
bigecho() { echo "## $1"; }

check_ip() {
  IP_REGEX='^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$'
  printf '%s' "$1" | tr -d '\n' | grep -Eq "$IP_REGEX"
}

vpnsetup() {

os_arch=$(uname -m | tr -dc 'A-Za-z0-9_-')
if ! grep -qs "Amazon Linux release 2" /etc/system-release; then
  echo "Error: This script only supports Amazon Linux 2." >&2
  echo "For Ubuntu/Debian, use https://git.io/vpnsetup" >&2
  echo "For CentOS/RHEL, use https://git.io/vpnsetup-centos" >&2
  exit 1
fi

if [ "$(id -u)" != 0 ]; then
  exiterr "Script must be run as root. Try 'sudo sh $0'"
fi

def_iface=$(route 2>/dev/null | grep -m 1 '^default' | grep -o '[^ ]*$')
[ -z "$def_iface" ] && def_iface=$(ip -4 route list 0/0 2>/dev/null | grep -m 1 -Po '(?<=dev )(\S+)')
def_state=$(cat "/sys/class/net/$def_iface/operstate" 2>/dev/null)
if [ -n "$def_state" ] && [ "$def_state" != "down" ]; then
  case $def_iface in
    wl*)
      exiterr "Wireless interface '$def_iface' detected. DO NOT run this script on your PC or Mac!"
      ;;
  esac
  NET_IFACE="$def_iface"
else
  eth0_state=$(cat "/sys/class/net/eth0/operstate" 2>/dev/null)
  if [ -z "$eth0_state" ] || [ "$eth0_state" = "down" ]; then
    exiterr "Could not detect the default network interface."
  fi
  NET_IFACE=eth0
fi

[ -n "$YOUR_IPSEC_PSK" ] && VPN_IPSEC_PSK="$YOUR_IPSEC_PSK"
[ -n "$YOUR_USERNAME" ] && VPN_USER="$YOUR_USERNAME"
[ -n "$YOUR_PASSWORD" ] && VPN_PASSWORD="$YOUR_PASSWORD"

if [ -z "$VPN_IPSEC_PSK" ] && [ -z "$VPN_USER" ] && [ -z "$VPN_PASSWORD" ]; then
  bigecho "VPN credentials not set by user. Generating random PSK and password..."
  VPN_IPSEC_PSK=$(LC_CTYPE=C tr -dc 'A-HJ-NPR-Za-km-z2-9' < /dev/urandom | head -c 20)
  VPN_USER=vpnuser
  VPN_PASSWORD=$(LC_CTYPE=C tr -dc 'A-HJ-NPR-Za-km-z2-9' < /dev/urandom | head -c 16)
fi

if [ -z "$VPN_IPSEC_PSK" ] || [ -z "$VPN_USER" ] || [ -z "$VPN_PASSWORD" ]; then
  exiterr "All VPN credentials must be specified. Edit the script and re-enter them."
fi

if printf '%s' "$VPN_IPSEC_PSK $VPN_USER $VPN_PASSWORD" | LC_ALL=C grep -q '[^ -~]\+'; then
  exiterr "VPN credentials must not contain non-ASCII characters."
fi

case "$VPN_IPSEC_PSK $VPN_USER $VPN_PASSWORD" in
  *[\\\"\']*)
    exiterr "VPN credentials must not contain these special characters: \\ \" '"
    ;;
esac

if { [ -n "$VPN_DNS_SRV1" ] && ! check_ip "$VPN_DNS_SRV1"; } \
  || { [ -n "$VPN_DNS_SRV2" ] && ! check_ip "$VPN_DNS_SRV2"; } then
  exiterr "The DNS server specified is invalid."
fi

bigecho "VPN setup in progress... Please be patient."

mkdir -p /opt/src
cd /opt/src || exit 1

bigecho "Installing packages required for setup..."

(
  set -x
  yum -y -q install wget bind-utils openssl tar \
    iptables iproute gawk grep sed net-tools >/dev/null
) || exiterr2

bigecho "Trying to auto discover IP of this server..."

# In case auto IP discovery fails, enter server's public IP here.
PUBLIC_IP=${VPN_PUBLIC_IP:-''}
[ -z "$PUBLIC_IP" ] && PUBLIC_IP=$(dig @resolver1.opendns.com -t A -4 myip.opendns.com +short)
check_ip "$PUBLIC_IP" || PUBLIC_IP=$(wget -t 3 -T 15 -qO- http://ipv4.icanhazip.com)
check_ip "$PUBLIC_IP" || exiterr "Cannot detect this server's public IP. Edit the script and manually enter it."

bigecho "Adding the EPEL repository..."

(
  set -x
  amazon-linux-extras install epel -y >/dev/null
) || exiterr2

bigecho "Installing packages required for the VPN..."

(
  set -x
  yum -y -q install nss-devel nspr-devel pkgconfig pam-devel \
    libcap-ng-devel libselinux-devel curl-devel nss-tools \
    flex bison gcc make util-linux ppp \
    systemd-devel iptables-services \
    libevent-devel fipscheck-devel >/dev/null
) || exiterr2
(
  set -x
  yum --enablerepo=epel -y -q install xl2tpd >/dev/null 2>&1
) || exiterr2

bigecho "Installing Fail2Ban to protect SSH..."

(
  set -x
  yum --enablerepo=epel -y -q install fail2ban >/dev/null
) || exiterr2

bigecho "Downloading IKEv2 script..."

ikev2_url="https://github.com/hwdsl2/setup-ipsec-vpn/raw/master/extras/ikev2setup.sh"
(
  set -x
  wget -t 3 -T 30 -q -O ikev2.sh "$ikev2_url"
) || /bin/rm -f ikev2.sh

bigecho "Downloading Libreswan..."

SWAN_VER=4.3
swan_file="libreswan-$SWAN_VER.tar.gz"
swan_url1="https://github.com/libreswan/libreswan/archive/v$SWAN_VER.tar.gz"
swan_url2="https://download.libreswan.org/$swan_file"
(
  set -x
  wget -t 3 -T 30 -q -O "$swan_file" "$swan_url1" || wget -t 3 -T 30 -q -O "$swan_file" "$swan_url2"
) || exit 1
/bin/rm -rf "/opt/src/libreswan-$SWAN_VER"
tar xzf "$swan_file" && /bin/rm -f "$swan_file"

bigecho "Compiling and installing Libreswan, please wait..."

cd "libreswan-$SWAN_VER" || exit 1
cat > Makefile.inc.local <<'EOF'
WERROR_CFLAGS=-w
USE_DNSSEC=false
USE_DH2=true
USE_NSS_KDF=false
FINALNSSDIR=/etc/ipsec.d
EOF
if ! grep -qs IFLA_XFRM_LINK /usr/include/linux/if_link.h; then
  echo "USE_XFRM_INTERFACE_IFLA_HEADER=true" >> Makefile.inc.local
fi
NPROCS=$(grep -c ^processor /proc/cpuinfo)
[ -z "$NPROCS" ] && NPROCS=1
(
  set -x
  make "-j$((NPROCS+1))" -s base >/dev/null && make -s install-base >/dev/null
)

cd /opt/src || exit 1
/bin/rm -rf "/opt/src/libreswan-$SWAN_VER"
if ! /usr/local/sbin/ipsec --version 2>/dev/null | grep -qF "$SWAN_VER"; then
  exiterr "Libreswan $SWAN_VER failed to build."
fi

bigecho "Creating VPN configuration..."

L2TP_NET=${VPN_L2TP_NET:-'192.168.42.0/24'}
L2TP_LOCAL=${VPN_L2TP_LOCAL:-'192.168.42.1'}
L2TP_POOL=${VPN_L2TP_POOL:-'192.168.42.10-192.168.42.250'}
XAUTH_NET=${VPN_XAUTH_NET:-'192.168.43.0/24'}
XAUTH_POOL=${VPN_XAUTH_POOL:-'192.168.43.10-192.168.43.250'}
DNS_SRV1=${VPN_DNS_SRV1:-'8.8.8.8'}
DNS_SRV2=${VPN_DNS_SRV2:-'8.8.4.4'}
DNS_SRVS="\"$DNS_SRV1 $DNS_SRV2\""
[ -n "$VPN_DNS_SRV1" ] && [ -z "$VPN_DNS_SRV2" ] && DNS_SRVS="$DNS_SRV1"

# Create IPsec config
conf_bk "/etc/ipsec.conf"
cat > /etc/ipsec.conf <<EOF
version 2.0

config setup
  virtual-private=%v4:10.0.0.0/8,%v4:192.168.0.0/16,%v4:172.16.0.0/12,%v4:!$L2TP_NET,%v4:!$XAUTH_NET
  interfaces=%defaultroute
  uniqueids=no

conn shared
  left=%defaultroute
  leftid=$PUBLIC_IP
  right=%any
  encapsulation=yes
  authby=secret
  pfs=no
  rekey=no
  keyingtries=5
  dpddelay=30
  dpdtimeout=120
  dpdaction=clear
  ikev2=never
  ike=aes256-sha2,aes128-sha2,aes256-sha1,aes128-sha1,aes256-sha2;modp1024,aes128-sha1;modp1024
  phase2alg=aes_gcm-null,aes128-sha1,aes256-sha1,aes256-sha2_512,aes128-sha2,aes256-sha2
  ikelifetime=24h
  salifetime=24h
  sha2-truncbug=no

conn l2tp-psk
  auto=add
  leftprotoport=17/1701
  rightprotoport=17/%any
  type=transport
  phase2=esp
  also=shared

conn xauth-psk
  auto=add
  leftsubnet=0.0.0.0/0
  rightaddresspool=$XAUTH_POOL
  modecfgdns=$DNS_SRVS
  leftxauthserver=yes
  rightxauthclient=yes
  leftmodecfgserver=yes
  rightmodecfgclient=yes
  modecfgpull=yes
  xauthby=file
  fragmentation=yes
  cisco-unity=yes
  also=shared

include /etc/ipsec.d/*.conf
EOF

# Specify IPsec PSK
conf_bk "/etc/ipsec.secrets"
cat > /etc/ipsec.secrets <<EOF
%any  %any  : PSK "$VPN_IPSEC_PSK"
EOF

# Create xl2tpd config
conf_bk "/etc/xl2tpd/xl2tpd.conf"
cat > /etc/xl2tpd/xl2tpd.conf <<EOF
[global]
port = 1701

[lns default]
ip range = $L2TP_POOL
local ip = $L2TP_LOCAL
require chap = yes
refuse pap = yes
require authentication = yes
name = l2tpd
pppoptfile = /etc/ppp/options.xl2tpd
length bit = yes
EOF

# Set xl2tpd options
conf_bk "/etc/ppp/options.xl2tpd"
cat > /etc/ppp/options.xl2tpd <<EOF
+mschap-v2
ipcp-accept-local
ipcp-accept-remote
noccp
auth
mtu 1280
mru 1280
proxyarp
lcp-echo-failure 4
lcp-echo-interval 30
connect-delay 5000
ms-dns $DNS_SRV1
EOF

if [ -z "$VPN_DNS_SRV1" ] || [ -n "$VPN_DNS_SRV2" ]; then
cat >> /etc/ppp/options.xl2tpd <<EOF
ms-dns $DNS_SRV2
EOF
fi

# Create VPN credentials
conf_bk "/etc/ppp/chap-secrets"
cat > /etc/ppp/chap-secrets <<EOF
"$VPN_USER" l2tpd "$VPN_PASSWORD" *
EOF

conf_bk "/etc/ipsec.d/passwd"
VPN_PASSWORD_ENC=$(openssl passwd -1 "$VPN_PASSWORD")
cat > /etc/ipsec.d/passwd <<EOF
$VPN_USER:$VPN_PASSWORD_ENC:xauth-psk
EOF

bigecho "Updating sysctl settings..."

if ! grep -qs "hwdsl2 VPN script" /etc/sysctl.conf; then
  conf_bk "/etc/sysctl.conf"
cat >> /etc/sysctl.conf <<EOF

# Added by hwdsl2 VPN script
kernel.msgmnb = 65536
kernel.msgmax = 65536

net.ipv4.ip_forward = 1
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.all.rp_filter = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.default.send_redirects = 0
net.ipv4.conf.default.rp_filter = 0
net.ipv4.conf.$NET_IFACE.send_redirects = 0
net.ipv4.conf.$NET_IFACE.rp_filter = 0

net.core.wmem_max = 12582912
net.core.rmem_max = 12582912
net.ipv4.tcp_rmem = 10240 87380 12582912
net.ipv4.tcp_wmem = 10240 87380 12582912
EOF
fi

F2B_FILE=/etc/fail2ban/jail.local
if [ ! -f "$F2B_FILE" ]; then
  bigecho "Creating basic Fail2Ban rules..."
cat > "$F2B_FILE" <<'EOF'
[ssh-iptables]
enabled = true
filter = sshd
logpath = /var/log/secure
action = iptables[name=SSH, port=ssh, protocol=tcp]
EOF
fi

bigecho "Updating IPTables rules..."

IPT_FILE=/etc/sysconfig/iptables
ipt_flag=0
if ! grep -qs "hwdsl2 VPN script" "$IPT_FILE"; then
  ipt_flag=1
fi

if [ "$ipt_flag" = "1" ]; then
  service fail2ban stop >/dev/null 2>&1
  iptables-save > "$IPT_FILE.old-$SYS_DT"
  iptables -I INPUT 1 -p udp --dport 1701 -m policy --dir in --pol none -j DROP
  iptables -I INPUT 2 -m conntrack --ctstate INVALID -j DROP
  iptables -I INPUT 3 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
  iptables -I INPUT 4 -p udp -m multiport --dports 500,4500 -j ACCEPT
  iptables -I INPUT 5 -p udp --dport 1701 -m policy --dir in --pol ipsec -j ACCEPT
  iptables -I INPUT 6 -p udp --dport 1701 -j DROP
  iptables -I FORWARD 1 -m conntrack --ctstate INVALID -j DROP
  iptables -I FORWARD 2 -i "$NET_IFACE" -o ppp+ -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
  iptables -I FORWARD 3 -i ppp+ -o "$NET_IFACE" -j ACCEPT
  iptables -I FORWARD 4 -i ppp+ -o ppp+ -s "$L2TP_NET" -d "$L2TP_NET" -j ACCEPT
  iptables -I FORWARD 5 -i "$NET_IFACE" -d "$XAUTH_NET" -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
  iptables -I FORWARD 6 -s "$XAUTH_NET" -o "$NET_IFACE" -j ACCEPT
  iptables -A FORWARD -j DROP
  iptables -t nat -I POSTROUTING -s "$XAUTH_NET" -o "$NET_IFACE" -m policy --dir out --pol none -j MASQUERADE
  iptables -t nat -I POSTROUTING -s "$L2TP_NET" -o "$NET_IFACE" -j MASQUERADE
  echo "# Modified by hwdsl2 VPN script" > "$IPT_FILE"
  iptables-save >> "$IPT_FILE"
fi

bigecho "Enabling services on boot..."

systemctl --now mask firewalld 2>/dev/null
systemctl enable iptables fail2ban 2>/dev/null

if ! grep -qs "hwdsl2 VPN script" /etc/rc.local; then
  if [ -f /etc/rc.local ]; then
    conf_bk "/etc/rc.local"
  else
    echo '#!/bin/sh' > /etc/rc.local
  fi
cat >> /etc/rc.local <<'EOF'

# Added by hwdsl2 VPN script
(sleep 15
service ipsec restart
service xl2tpd restart
echo 1 > /proc/sys/net/ipv4/ip_forward)&
EOF
fi

bigecho "Starting services..."

restorecon /etc/ipsec.d/*db 2>/dev/null
restorecon /usr/local/sbin -Rv 2>/dev/null
restorecon /usr/local/libexec/ipsec -Rv 2>/dev/null

sysctl -e -q -p

chmod +x /etc/rc.local
chmod 600 /etc/ipsec.secrets* /etc/ppp/chap-secrets* /etc/ipsec.d/passwd*

iptables-restore < "$IPT_FILE"

# Fix xl2tpd if l2tp_ppp is unavailable
if ! modprobe -q l2tp_ppp; then
  sed -i '/^ExecStartPre=\//s/=/=-/' /usr/lib/systemd/system/xl2tpd.service
  systemctl daemon-reload
fi

mkdir -p /run/pluto
service fail2ban restart 2>/dev/null
service ipsec restart 2>/dev/null
service xl2tpd restart 2>/dev/null

swan_ver_url="https://dl.ls20.com/v1/amzn/2/swanver?arch=$os_arch&ver=$SWAN_VER"
swan_ver_latest=$(wget -t 3 -T 15 -qO- "$swan_ver_url")
if printf '%s' "$swan_ver_latest" | grep -Eq '^([3-9]|[1-9][0-9])\.([0-9]|[1-9][0-9])$' \
  && [ -n "$SWAN_VER" ] && [ "$SWAN_VER" != "$swan_ver_latest" ] \
  && printf '%s\n%s' "$SWAN_VER" "$swan_ver_latest" | sort -C -V; then
cat <<EOF

Note: A newer version of Libreswan ($swan_ver_latest) is available.
      To update, run:
      wget https://git.io/vpnupgrade-amzn -O vpnupgrade.sh
      sudo sh vpnupgrade.sh
EOF
fi

cat <<EOF

================================================

IPsec VPN server is now ready for use!

Connect to your new VPN with these details:

Server IP: $PUBLIC_IP
IPsec PSK: $VPN_IPSEC_PSK
Username: $VPN_USER
Password: $VPN_PASSWORD

Write these down. You'll need them to connect!

Important notes:   https://git.io/vpnnotes
Setup VPN clients: https://git.io/vpnclients
IKEv2 guide:       https://git.io/ikev2

================================================

EOF

}

## Defer setup until we have the complete script
vpnsetup "$@"

exit 0