#!/bin/bash -x
# Copyright (C) 2016 Ian Kelling

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


set -eE -o pipefail
trap 'echo "$0:$LINENO:error: \"$BASH_COMMAND\" returned $?" >&2' ERR

[[ $EUID == 0 ]] || exec sudo -E "$BASH_SOURCE" "$@"

usage() {
  cat <<'EOF'
usage: ${0##*/} [-d|-h|--help] [IPV6_ADDR/BITS IPV6_DEFAULT_ROUTE]

-r  Do not push default route
-d  Do not push dns
-s  Do not start openvpn
-h --help print help

Sets up a vpn server which pushes gateway route and dns server so all
traffic goes through the vpn. requires systemd, and might have some
debian specific paths.

For ipv6, we assume ipv6_addr routes to the server.

You can save all the keys by storing /etc/openvpn/easy-rsa/keys, and
the script will not generate them if it sees they exist already.

Note: Uses GNU getopt options parsing style
EOF
  exit $1
}

dns=true
route=true
start=true
temp=$(getopt -l help drsh "$@") || usage 1
eval set -- "$temp"
while true; do
  case $1 in
    -d) dns=false; shift ;;
    -r) route=false; shift ;;
    -s) start=false; shift ;;
    -h|--help) usage ;;
    --) shift; break ;;
    *) echo "$0: Internal error! unexpected args: $*" ; exit 1 ;;
  esac
done

read -r ip6 ip6route <<<"$@"


apt-get update
# suggests get's us openssl. policy-rc.d is to prevent install from starting services
f=/usr/sbin/policy-rc.d;
dd of=$f <<EOF
#!/bin/sh
exit 101
EOF
chmod +x $f;
apt-get install --install-suggests -y openvpn
rm $f

if [[ -e /lib/systemd/system/openvpn-server@.service ]]; then
  vpn_service=openvpn-server@server
else
  vpn_service=openvpn@server
fi
apt-get install -y uuid-runtime easy-rsa
mkdir -p /etc/openvpn/easy-rsa
cd /etc/openvpn/easy-rsa
cp -r /usr/share/easy-rsa/* .
if [[ -e openssl-1.0.0.cnf && ! -e openssl.cnf ]]; then
  # there's a debian bug about this.
  ln -s openssl-1.0.0.cnf openssl.cnf
fi

server_dir=/etc/openvpn/server
mkdir -p $server_dir
chmod 700 $server_dir


new=true
keyfiles=(/etc/openvpn/easy-rsa/pki/{ca.crt,private/server.key,issued/server.crt})
if [[ -e /etc/openvpn/easy-rsa/build-ca ]]; then
  new=false
  keyfiles=(/etc/openvpn/easy-rsa/keys/{ca.crt,server.{crt,key}})
fi

keys_exist=true
for f in ${keyfiles[@]}; do
  if [[ ! -e $f ]]; then
    keys_exist=false
    break
  fi
done

if ! $keys_exist; then
  # newer sample configs (post stretch) use ta.key. no harm making it for earlier oses
  openvpn --genkey --secret $server_dir/ta.key
  if $new; then
    ./easyrsa init-pki
    ./easyrsa --batch build-ca nopass
    ./easyrsa build-server-full server nopass
    openssl dhparam -out $server_dir/dh2048.pem 2048
  else
    # dun care about settning cert cn etc from the non-example values
    source vars
    # doesnt exist in buster
    ./clean-all # note: removes and creates /etc/openvpn/easy-rsa/keys
    # accept default prompts
    echo -e '\n\n\n\n\n\n\n\n' | ./build-ca

    # This builds the server's key/cert. argument is the name of the file,
    # but it also is the default common name of the cert.
    # 'server' is the default name in our conf file for the name of the file
    # and I've seen no reason to change it.
    # Note, this is not idempotent.
    { echo -e '\n\n\n\n\n\n\n\n\n\n'; sleep 1; echo -e 'y\ny\n'; } | ./build-key-server server
    ./build-dh
  fi
fi


cp /usr/share/doc/openvpn/examples/sample-config-files/server.conf.gz $server_dir
gzip -df $server_dir/server.conf.gz


cp ${keyfiles[@]} $server_dir
# for legacy systems
for f in ${keyfiles[@]}; do
  ln -sf server/${f##*/} /etc/openvpn
done

cat >>$server_dir/server.conf <<'EOF'

# I cat an extra blank line to start because the example config does
# not have a final newline. ....

# not in example config, but openvpn outputs a warning about insecure
# cipher without a setting like this (the default i can understand due
# to compatibility issues, but not changing the example config... not
# cool).
# requires the same setting on the client side.
cipher AES-256-CBC
# just sets up the ability to have client specific configs
client-config-dir /etc/openvpn/client-config

# duplicate in newer sample configs
tls-auth ta.key 0 # This file is secret

# depending on sample config, this may not be there, which means i can't
# talk to 10.8.0.1, there might be some other way, but stretch's
# sample config says:
# Should be subnet (addressing via IP)
# unless Windows clients v2.0.9 and lower have to
# be supported (then net30, i.e. a /30 per client)
# Defaults to net30 (not recommended)
topology subnet
EOF


# dh improve security,
# remove comp-lzo to increase perf
sed -i --follow-symlinks -f - $server_dir/server.conf <<'EOF'
s/^dh dh1024.pem/dh dh2048.pem/
/^comp-lzo.*/d
EOF


mkdir -p /etc/openvpn/client-config


if $dns; then
  # Be the dns server for clients
  cat >>$server_dir/server.conf <<'EOF'
push "dhcp-option DNS 10.8.0.1"
EOF
fi

if $ip6; then
  cat >>$server_dir/server.conf <<EOF
push tun-ipv6 # legacy option that flidas needs, has no harm.
ifconfig-ipv6 $ip6 $ip6_route
EOF
fi


if $route; then
  cat >>$server_dir/server.conf <<'EOF'
# Be the default gateway for clients.
push "redirect-gateway def1"
EOF
  if $ip6; then
    cat >>$server_dir/server.conf <<'EOF'
push "route-ipv6 2000::/3"
EOF
  fi
fi

sed -i --follow-symlinks '/^ *net\.ipv4\.ip_forward=.*/d' /etc/sysctl.conf
sed -i --follow-symlinks '/^ *net.ipv6.conf.all.forwarding=.*/d' /etc/sysctl.conf
cat >>/etc/sysctl.conf <<'EOF'
net.ipv4.ip_forward=1
net.ipv6.conf.all.forwarding=1
EOF
sysctl -p /etc/sysctl.conf

gw=$(ip route | sed -rn 's/^default via .* dev (\S+).*/\1/p')

cat >/etc/systemd/system/vpnnat.service <<EOF
[Unit]
Description=Turns on nat iptables setting

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/sbin/iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o $gw -j MASQUERADE
ExecStop=/sbin/iptables -t nat -D POSTROUTING -s 10.8.0.0/24 -o $gw -j MASQUERADE

[Install]
WantedBy=$vpn_service.service
EOF
systemctl daemon-reload # needed if the file was already there
# note, no need to start it, the vpn_service does that.
systemctl enable vpnnat

if $start; then
  systemctl enable $vpn_service
  systemctl restart $vpn_service
fi