#!/bin/bash
# https://github.com/birkhoffcheng/openvpn-install

# Detect Debian users running the script with "sh" instead of bash
if readlink /proc/$$/exe | grep -q "dash"; then
	echo "This script needs to be run with bash, not sh"
	exit
fi

if [[ "$EUID" -ne 0 ]]; then
	echo "Sorry, you need to run this as root"
	exit
fi

if [[ ! -e /dev/net/tun ]]; then
	echo "The TUN device is not available
You need to enable TUN before running this script"
	exit
fi

if [[ -e /etc/debian_version ]]; then
	OS=debian
	GROUPNAME=nogroup
	RCLOCAL='/etc/rc.local'
elif [[ -e /etc/centos-release || -e /etc/redhat-release ]]; then
	OS=centos
	GROUPNAME=nobody
	RCLOCAL='/etc/rc.d/rc.local'
else
	echo "Looks like you aren't running this installer on Debian, Ubuntu or CentOS"
	exit
fi

newclient () {
	# Generates the custom client.ovpn
	cp /etc/openvpn/client-common.txt ~/$1.ovpn
	echo "<ca>" >> ~/$1.ovpn
	cat /etc/openvpn/easy-rsa/pki/ca.crt >> ~/$1.ovpn
	echo "</ca>" >> ~/$1.ovpn
	echo "<cert>" >> ~/$1.ovpn
	cat /etc/openvpn/easy-rsa/pki/issued/$1.crt >> ~/$1.ovpn
	echo "</cert>" >> ~/$1.ovpn
	echo "<key>" >> ~/$1.ovpn
	cat /etc/openvpn/easy-rsa/pki/private/$1.key >> ~/$1.ovpn
	echo "</key>" >> ~/$1.ovpn
	echo "<tls-auth>" >> ~/$1.ovpn
	cat /etc/openvpn/ta.key >> ~/$1.ovpn
	echo "</tls-auth>" >> ~/$1.ovpn
}

if [[ -e /etc/openvpn/server.conf ]]; then
	while :
	do
	clear
		echo "Looks like OpenVPN is already installed."
		echo
		echo "What do you want to do?"
		echo "   1) Add a new user"
		echo "   2) Revoke an existing user"
		echo "   3) Remove OpenVPN"
		echo "   4) Exit"
		read -p "Select an option [1-4]: " option
		case $option in
			1)
			echo
			echo "Tell me a name for the client certificate."
			echo "Please, use one word only, no special characters."
			read -p "Client name: " -e CLIENT
			cd /etc/openvpn/easy-rsa/
			easyrsa build-client-full $CLIENT nopass
			newclient "$CLIENT"
			echo
			echo "Client $CLIENT added, configuration is available at:" ~/"$CLIENT.ovpn"
			if [ -f /etc/stunnel/stunnel-client.conf ]; then
				cp /etc/stunnel/stunnel-client.conf $HOME/stunnel.conf
				cp /etc/openvpn/server.crt $HOME/stunnel.crt
				echo "~/stunnel.crt and ~/stunnel.conf."
			fi
			exit
			;;
			2)
			# This option could be documented a bit better and maybe even be simplified
			# ...but what can I say, I want some sleep too
			NUMBEROFCLIENTS=$(tail -n +2 /etc/openvpn/easy-rsa/pki/index.txt | grep -c "^V")
			if [[ "$NUMBEROFCLIENTS" = '0' ]]; then
				echo
				echo "You have no existing clients!"
				exit
			fi
			echo
			echo "Select the existing client certificate you want to revoke:"
			tail -n +2 /etc/openvpn/easy-rsa/pki/index.txt | grep "^V" | cut -d '=' -f 2 | nl -s ') '
			if [[ "$NUMBEROFCLIENTS" = '1' ]]; then
				read -p "Select one client [1]: " CLIENTNUMBER
			else
				read -p "Select one client [1-$NUMBEROFCLIENTS]: " CLIENTNUMBER
			fi
			CLIENT=$(tail -n +2 /etc/openvpn/easy-rsa/pki/index.txt | grep "^V" | cut -d '=' -f 2 | sed -n "$CLIENTNUMBER"p)
			echo
			read -p "Do you really want to revoke access for client $CLIENT? [y/N]: " -e REVOKE
			if [[ "$REVOKE" = 'y' || "$REVOKE" = 'Y' ]]; then
				cd /etc/openvpn/easy-rsa/
				easyrsa --batch revoke $CLIENT
				EASYRSA_CRL_DAYS=3650 easyrsa gen-crl
				rm -f pki/reqs/$CLIENT.req
				rm -f pki/private/$CLIENT.key
				rm -f pki/issued/$CLIENT.crt
				rm -f /etc/openvpn/crl.pem
				cp /etc/openvpn/easy-rsa/pki/crl.pem /etc/openvpn/crl.pem
				# CRL is read with each client connection, when OpenVPN is dropped to nobody
				chown nobody:$GROUPNAME /etc/openvpn/crl.pem
				echo
				echo "Certificate for client $CLIENT revoked!"
			else
				echo
				echo "Certificate revocation for client $CLIENT aborted!"
			fi
			exit
			;;
			3)
			echo
			read -p "Do you really want to remove OpenVPN? [y/N]: " -e REMOVE
			if [[ "$REMOVE" = 'y' || "$REMOVE" = 'Y' ]]; then
				PORT=$(grep '^port ' /etc/openvpn/server.conf | cut -d " " -f 2)
				PROTOCOL=$(grep '^proto ' /etc/openvpn/server.conf | cut -d " " -f 2)
				if pgrep firewalld; then
					IP=$(firewall-cmd --direct --get-rules ipv4 nat POSTROUTING | grep '\-s 10.8.0.0/24 '"'"'!'"'"' -d 10.8.0.0/24 -j SNAT --to ' | cut -d " " -f 10)
					# Using both permanent and not permanent rules to avoid a firewalld reload.
					firewall-cmd --zone=public --remove-port=$PORT/$PROTOCOL
					firewall-cmd --zone=trusted --remove-source=10.8.0.0/24
					firewall-cmd --permanent --zone=public --remove-port=$PORT/$PROTOCOL
					firewall-cmd --permanent --zone=trusted --remove-source=10.8.0.0/24
					firewall-cmd --direct --remove-rule ipv4 nat POSTROUTING 0 -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to $IP
					firewall-cmd --permanent --direct --remove-rule ipv4 nat POSTROUTING 0 -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to $IP
				else
					IP=$(grep 'iptables -t nat -A POSTROUTING -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to ' $RCLOCAL | cut -d " " -f 14)
					iptables -t nat -D POSTROUTING -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to $IP
					sed -i '/iptables -t nat -A POSTROUTING -s 10.8.0.0\/24 ! -d 10.8.0.0\/24 -j SNAT --to /d' $RCLOCAL
					if iptables -L -n | grep -qE '^ACCEPT'; then
						iptables -D INPUT -p $PROTOCOL --dport $PORT -j ACCEPT
						iptables -D FORWARD -s 10.8.0.0/24 -j ACCEPT
						iptables -D FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
						sed -i "/iptables -I INPUT -p $PROTOCOL --dport $PORT -j ACCEPT/d" $RCLOCAL
						sed -i "/iptables -I FORWARD -s 10.8.0.0\/24 -j ACCEPT/d" $RCLOCAL
						sed -i "/iptables -I FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT/d" $RCLOCAL
					fi
				fi
				if sestatus 2>/dev/null | grep "Current mode" | grep -q "enforcing" && [[ "$PORT" != '1194' ]]; then
					semanage port -d -t openvpn_port_t -p $PROTOCOL $PORT
				fi
				if [[ "$OS" = 'debian' ]]; then
					apt remove --purge openvpn stunnel4 easy-rsa -y
				else
					yum remove openvpn stunnel4 easy-rsa -y
				fi
				rm -rf /etc/openvpn /etc/stunnel
				rm -f /etc/sysctl.d/30-openvpn-forward.conf
				echo
				echo "OpenVPN removed!"
			else
				echo
				echo "Removal aborted!"
			fi
			exit
			;;
			4) exit;;
		esac
	done
else
	clear
	echo 'Welcome to OpenVPN installer!'
	echo
	# OpenVPN setup and first user creation
	echo "I need to ask you a few questions before starting the setup."
	echo "You can leave the default options and just press enter if you are ok with them."
	echo
	echo "First, provide the IPv4 address of the network interface you want OpenVPN"
	echo "listening to."
	# Autodetect IP address and pre-fill for the user
	IP=$(ip addr | grep 'inet' | grep -v inet6 | grep -vE '127\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' | grep -oE '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' | head -1)
	read -p "IP address: " -e -i $IP IP
	# If $IP is a private IP address, the server must be behind NAT
	if echo "$IP" | grep -qE '^(10\.|172\.1[6789]\.|172\.2[0-9]\.|172\.3[01]\.|192\.168)'; then
		echo
		echo "This server is behind NAT. What is the public IPv4 address or hostname?"
		read -p "Public IP address / hostname: " -e PUBLICIP
	fi
	echo
	echo "Which protocol do you want for OpenVPN connections?"
	echo "   1) UDP (recommended)"
	echo "   2) TCP"
	echo "   3) OpenVPN over SSL"
	read -p "Protocol [1-3]: " -e -i 1 PROTOCOLCHOICE
	case $PROTOCOLCHOICE in
		1)
		PROTOCOL=udp
		SSL=0
		;;
		2)
		PROTOCOL=tcp
		SSL=0
		;;
		3)
		PROTOCOL=tcp
		SSL=1
		;;
	esac
	echo
	echo "What port do you want OpenVPN listening to?"
	read -p "Port: " -e -i 443 PORT
	echo
	echo "Which cipher mode do you want to use?"
	echo "   1) AES-256-GCM (provides authenticated encryption)"
	echo "   2) AES-256-CBC (compatible with versions of OpenVPN older than 2.4)"
	read -p "Cipher Mode [1-2]: " -e -i 1 CIPHERCHOICE
	case $CIPHERCHOICE in
		1)
		CIPHER=AES-256-GCM
		;;
		2)
		CIPHER=AES-256-CBC
		;;
	esac
	echo
	echo "Which DNS do you want to use with the VPN?"
	echo "   1) Current system resolvers"
	echo "   2) 1.1.1.1"
	echo "   3) Google"
	echo "   4) OpenDNS"
	echo "   5) Verisign"
	read -p "DNS [1-5]: " -e -i 1 DNS
	echo
	echo "Finally, tell me your name for the client certificate."
	echo "Please, use one word only, no special characters."
	read -p "Client name: " -e -i client CLIENT
	read -p "For how long should each session key be used? (seconds) " -e -i 3600 RENEGKEY
	echo
	echo "Okay, that was all I needed. We are ready to set up your OpenVPN server now."
	read -n1 -r -p "Press any key to continue..."
	if [[ "$OS" = 'debian' ]]; then
		apt update
		apt dist-upgrade -y
		apt install openvpn iptables openssl ca-certificates stunnel4 easy-rsa -y
	else
		# Else, the distro is CentOS
		yum install epel-release -y
		yum install openvpn iptables openssl ca-certificates stunnel4 easy-rsa -y
	fi
	mkdir /etc/openvpn/easy-rsa/
	cd /etc/openvpn/easy-rsa/
	# Create the PKI, set up the CA, the DH params and the server + client certificates
	easyrsa init-pki
	easyrsa --batch build-ca nopass
	easyrsa gen-dh
	easyrsa build-server-full server nopass
	easyrsa build-client-full $CLIENT nopass
	EASYRSA_CRL_DAYS=3650 easyrsa gen-crl
	# Move the stuff we need
	csplit -f /etc/openvpn/easy-rsa/pki/issued/cert. /etc/openvpn/easy-rsa/pki/issued/server.crt '/-----BEGIN CERTIFICATE-----/' '{*}'
	rm /etc/openvpn/easy-rsa/pki/issued/cert.00 /etc/openvpn/easy-rsa/pki/issued/server.crt
	mv /etc/openvpn/easy-rsa/pki/issued/cert.01 /etc/openvpn/easy-rsa/pki/issued/server.crt
	cp pki/ca.crt pki/private/ca.key pki/dh.pem pki/issued/server.crt pki/private/server.key pki/crl.pem /etc/openvpn
	# CRL is read with each client connection, when OpenVPN is dropped to nobody
	chown nobody:$GROUPNAME /etc/openvpn/crl.pem
	# Generate key for tls-auth
	openvpn --genkey --secret /etc/openvpn/ta.key
	# Generate server.conf
	if [[ $SSL==1 ]]; then
		echo "local 127.0.0.1" > /etc/openvpn/server.conf
		echo "port 1194" >> /etc/openvpn/server.conf
		echo "sslVersion = all
;chroot = /var/lib/stunnel4/
pid = /var/run/stunnel4.pid
debug = 7
output = /var/log/stunnel4/stunnel.log
socket = l:TCP_NODELAY=1
socket = r:TCP_NODELAY=1
[openvpn]
accept = 0.0.0.0:$PORT
connect = 127.0.0.1:1194
cert=/etc/openvpn/server.crt
key=/etc/openvpn/server.key" > /etc/stunnel/stunnel.conf
		echo 'ENABLED=1
FILES="/etc/stunnel/*.conf"
OPTIONS=""
PPP_RESTART=0
RLIMITS=""' > /etc/default/stunnel4
	else
		echo "port $PORT" > /etc/openvpn/server.conf
	fi
	echo "proto $PROTOCOL
dev tun
sndbuf 0
rcvbuf 0
ca ca.crt
cert server.crt
key server.key
dh dh.pem
auth SHA512
tls-auth ta.key 0
topology subnet
server 10.8.0.0 255.255.255.0
ifconfig-pool-persist ipp.txt" >> /etc/openvpn/server.conf
	echo 'push "redirect-gateway def1 bypass-dhcp"' >> /etc/openvpn/server.conf
	# DNS
	case $DNS in
		1)
		# Locate the proper resolv.conf
		# Needed for systems running systemd-resolved
		if grep -q "127.0.0.53" "/etc/resolv.conf"; then
			RESOLVCONF='/run/systemd/resolve/resolv.conf'
		else
			RESOLVCONF='/etc/resolv.conf'
		fi
		# Obtain the resolvers from resolv.conf and use them for OpenVPN
		grep -v '#' $RESOLVCONF | grep 'nameserver' | grep -E -o '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' | while read line; do
			echo "push \"dhcp-option DNS $line\"" >> /etc/openvpn/server.conf
		done
		;;
		2)
		echo 'push "dhcp-option DNS 1.1.1.1"' >> /etc/openvpn/server.conf
		echo 'push "dhcp-option DNS 1.0.0.1"' >> /etc/openvpn/server.conf
		;;
		3)
		echo 'push "dhcp-option DNS 8.8.8.8"' >> /etc/openvpn/server.conf
		echo 'push "dhcp-option DNS 8.8.4.4"' >> /etc/openvpn/server.conf
		;;
		4)
		echo 'push "dhcp-option DNS 208.67.222.222"' >> /etc/openvpn/server.conf
		echo 'push "dhcp-option DNS 208.67.220.220"' >> /etc/openvpn/server.conf
		;;
		5)
		echo 'push "dhcp-option DNS 64.6.64.6"' >> /etc/openvpn/server.conf
		echo 'push "dhcp-option DNS 64.6.65.6"' >> /etc/openvpn/server.conf
		;;
	esac
	echo "keepalive 10 120
cipher $CIPHER
comp-lzo
user nobody
group $GROUPNAME
persist-key
persist-tun
status openvpn-status.log
verb 3
crl-verify crl.pem" >> /etc/openvpn/server.conf
	# Enable net.ipv4.ip_forward for the system
	echo 'net.ipv4.ip_forward=1' > /etc/sysctl.d/30-openvpn-forward.conf
	# Enable without waiting for a reboot or service restart
	echo 1 > /proc/sys/net/ipv4/ip_forward
	if pgrep firewalld; then
		# Using both permanent and not permanent rules to avoid a firewalld
		# reload.
		# We don't use --add-service=openvpn because that would only work with
		# the default port and protocol.
		firewall-cmd --zone=public --add-port=$PORT/$PROTOCOL
		firewall-cmd --zone=trusted --add-source=10.8.0.0/24
		firewall-cmd --permanent --zone=public --add-port=$PORT/$PROTOCOL
		firewall-cmd --permanent --zone=trusted --add-source=10.8.0.0/24
		# Set NAT for the VPN subnet
		firewall-cmd --direct --add-rule ipv4 nat POSTROUTING 0 -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to $IP
		firewall-cmd --permanent --direct --add-rule ipv4 nat POSTROUTING 0 -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to $IP
	else
		# Needed to use rc.local with some systemd distros
		if [[ "$OS" = 'debian' && ! -e $RCLOCAL ]]; then
			echo '#!/bin/sh -e
exit 0' > $RCLOCAL
		fi
		chmod +x $RCLOCAL
		# Set NAT for the VPN subnet
		iptables -t nat -A POSTROUTING -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to $IP
		sed -i "1 a\iptables -t nat -A POSTROUTING -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to $IP" $RCLOCAL
		if iptables -L -n | grep -qE '^(REJECT|DROP)'; then
			# If iptables has at least one REJECT rule, we asume this is needed.
			# Not the best approach but I can't think of other and this shouldn't
			# cause problems.
			iptables -I INPUT -p $PROTOCOL --dport $PORT -j ACCEPT
			iptables -I FORWARD -s 10.8.0.0/24 -j ACCEPT
			iptables -I FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
			sed -i "1 a\iptables -I INPUT -p $PROTOCOL --dport $PORT -j ACCEPT" $RCLOCAL
			sed -i "1 a\iptables -I FORWARD -s 10.8.0.0/24 -j ACCEPT" $RCLOCAL
			sed -i "1 a\iptables -I FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT" $RCLOCAL
		fi
	fi
	# If SELinux is enabled and a custom port was selected, we need this
	if sestatus 2>/dev/null | grep "Current mode" | grep -q "enforcing" && [[ "$PORT" != '1194' ]]; then
		# Install semanage if not already present
		if ! hash semanage 2>/dev/null; then
			yum install policycoreutils-python -y
		fi
		semanage port -a -t openvpn_port_t -p $PROTOCOL $PORT
	fi
	# And finally, restart OpenVPN
	if [[ "$OS" = 'debian' ]]; then
		# Little hack to check for systemd
		if pgrep systemd-journal; then
			systemctl restart openvpn@server.service
		else
			/etc/init.d/openvpn restart
		fi
	else
		if pgrep systemd-journal; then
			systemctl restart openvpn@server.service
			systemctl enable openvpn@server.service
		else
			service openvpn restart
			chkconfig openvpn on
		fi
	fi
	# If the server is behind a NAT, use the correct IP address
	if [[ "$PUBLICIP" != "" ]]; then
		IP=$PUBLICIP
	fi
	# client-common.txt is created so we have a template to add further users later
	echo "client
dev tun
proto $PROTOCOL
sndbuf 0
rcvbuf 0" > /etc/openvpn/client-common.txt
	if [[ $SSL=1 ]]; then
		echo "remote 127.0.0.1 1194" >> /etc/openvpn/client-common.txt
	else
		echo "remote $IP $PORT" >> /etc/openvpn/client-common.txt
	fi
	echo "resolv-retry infinite
nobind
persist-key
persist-tun
remote-cert-tls server
auth SHA512
cipher $CIPHER
comp-lzo
setenv opt block-outside-dns
key-direction 1
reneg-sec $RENEGKEY
verb 3" >> /etc/openvpn/client-common.txt
	if [[ $SSL=1 ]]; then
		echo "client = yes
debug = 7
[openvpn]
accept = 127.0.0.1:1194
connect = $IP:$PORT
verify = 2
CAfile = stunnel.crt
TIMEOUTclose = 1000
session=300
stack=65536
sslVersion=TLSv1.2" > /etc/stunnel/stunnel-client.conf
	cp /etc/stunnel/stunnel-client.conf $HOME/stunnel.conf
	cp /etc/openvpn/server.crt $HOME/stunnel.crt
	fi
	# Generates the custom client.ovpn
	newclient "$CLIENT"
	echo
	echo "Finished!"
	echo
	echo "Your client configuration is available at: ~/$CLIENT.ovpn"
	if [[ $SSL=1 ]]; then
		echo "~/stunnel.crt and ~/stunnel.conf."
	fi
	echo "If you want to add more clients, you simply need to run this script again!"
fi