mailinabox/setup/system.sh

source /etc/mailinabox.conf
source setup/functions.sh # load our functions

# Basic System Configuration
# -------------------------

# ### Disable password login via SSH

# We will disable password based login via ssh only if the user that logged in:
#
# - Is using an ssh connection
# - Used a public key to authenticate
# - The user still has that key in authorized_keys
#
# The /var/log/auth.log will contain entries for logins that used public
# key authentication. We will try to find an entry for the user. If we
# find a record matching the user and the current ip address we will lookup
# the key finger print in the authorized keys of the user
#
# Sudo makes the use of $SSH_CLIENT client impossible, so we have to use pinky
USERNAME_THAT_WAS_USED_TO_LOG_IN=$(logname)
IP_ADDRESS_OF_USER=$(pinky -w $USERNAME_THAT_WAS_USED_TO_LOG_IN | tail -n+2 | tail -n1 | awk '{print $(NF)}')
if [ ! -z "$IP_ADDRESS_OF_USER" ]; then
	HOMEDIRECTORY_OF_USER=$(grep "$USERNAME_THAT_WAS_USED_TO_LOG_IN" /etc/passwd | cut -d":" -f6)
	LOG_ENTRY_TO_SEARCH_FOR="ssh.* Accepted publickey for $USERNAME_THAT_WAS_USED_TO_LOG_IN from $IP_ADDRESS_OF_USER"
	SSH_PUB_KEY_USED_TO_LOG_IN=$(grep "$LOG_ENTRY_TO_SEARCH_FOR" /var/log/auth.log* | tail -n 1 | awk '{print $(NF)}')

	if [ ! -z "$SSH_PUB_KEY_USED_TO_LOG_IN" ]; then
	if [ -e "$HOMEDIRECTORY_OF_USER"/.ssh/authorized_keys ]; then
	if ssh-keygen -l -f "$HOMEDIRECTORY_OF_USER"/.ssh/authorized_keys | grep -q -i "$SSH_PUB_KEY_USED_TO_LOG_IN"; then
		# Public key used to log in is still in authorized_keys so we can safely disable
		# password based logins
		echo "Disabling password authentication for ssh"
		tools/editconf.py /etc/ssh/sshd_config -s \
			PasswordAuthentication=no

		restart_service ssh
	fi
	fi
	fi
fi

# ### Add swap space to the system

# If the physical memory of the system is below 2GB it is wise to create a
# swap file. This will make the system more resiliant to memory spikes and
# prevent for instance spam filtering from crashing

# We will create a 1G file, this should be a good balance between disk usage
# and buffers for the system. We will only allocate this file if there is more
# than 5GB of disk space available

# The following checks are performed:
# - Check if swap is currently mountend by looking at /proc/swaps
# - Check if the user intents to activate swap on next boot by checking fstab entries.
# - Check if a swapfile already exists
# - Check if the root file system is not btrfs, might be an incompatible version with
#   swapfiles. User should hanle it them selves.
# - Check the memory requirements
# - Check available diskspace

# See https://www.digitalocean.com/community/tutorials/how-to-add-swap-on-ubuntu-14-04
# for reference

SWAP_MOUNTED=$(cat /proc/swaps | tail -n+2)
SWAP_IN_FSTAB=$(grep "swap" /etc/fstab)
ROOT_IS_BTRFS=$(grep "\/ .*btrfs" /proc/mounts)
TOTAL_PHYSICAL_MEM=$(head -n 1 /proc/meminfo | awk '{print $2}')
AVAILABLE_DISK_SPACE=$(df / --output=avail | tail -n 1)
if
	[ -z "$SWAP_MOUNTED" ] &&
	[ -z "$SWAP_IN_FSTAB" ] &&
	[ ! -e /swapfile ] &&
	[ -z "$ROOT_IS_BTRFS" ] &&
	[ $TOTAL_PHYSICAL_MEM -lt 1900000 ] &&
	[ $AVAILABLE_DISK_SPACE -gt 5242880 ]
then
	echo "Adding a swap file to the system..."

	# Allocate and activate the swap file. Allocate in 1KB chuncks
	# doing it in one go, could fail on low memory systems
	dd if=/dev/zero of=/swapfile bs=1024 count=$[1024*1024] status=none
	if [ -e /swapfile ]; then
		chmod 600 /swapfile
		hide_output mkswap /swapfile
		swapon /swapfile
	fi

	# Check if swap is mounted then activate on boot
	if swapon -s | grep -q "\/swapfile"; then
		echo "/swapfile   none    swap    sw    0   0" >> /etc/fstab
	else
		echo "ERROR: Swap allocation failed"
	fi
fi

# ### Add Mail-in-a-Box's PPA.

# We've built several .deb packages on our own that we want to include.
# One is a replacement for Ubuntu's stock postgrey package that makes
# some enhancements. The other is dovecot-lucene, a Lucene-based full
# text search plugin for (and by) dovecot, which is not available in
# Ubuntu currently.
#
# So, first ensure add-apt-repository is installed, then use it to install
# the [mail-in-a-box ppa](https://launchpad.net/~mail-in-a-box/+archive/ubuntu/ppa).


if [ ! -f /usr/bin/add-apt-repository ]; then
	echo "Installing add-apt-repository..."
	hide_output apt-get update
	apt_install software-properties-common
fi

hide_output add-apt-repository -y ppa:mail-in-a-box/ppa

# ### Update Packages

# Update system packages to make sure we have the latest upstream versions of things from Ubuntu.

echo Updating system packages...
hide_output apt-get update
apt_get_quiet upgrade

# ### Install System Packages

# Install basic utilities.
#
# * haveged: Provides extra entropy to /dev/random so it doesn't stall
#	         when generating random numbers for private keys (e.g. during
#	         ldns-keygen).
# * unattended-upgrades: Apt tool to install security updates automatically.
# * cron: Runs background processes periodically.
# * ntp: keeps the system time correct
# * fail2ban: scans log files for repeated failed login attempts and blocks the remote IP at the firewall
# * netcat-openbsd: `nc` command line networking tool
# * git: we install some things directly from github
# * sudo: allows privileged users to execute commands as root without being root
# * coreutils: includes `nproc` tool to report number of processors, mktemp
# * bc: allows us to do math to compute sane defaults

echo Installing system packages...
apt_install python3 python3-dev python3-pip \
	netcat-openbsd wget curl git sudo coreutils bc \
	haveged pollinate \
	unattended-upgrades cron ntp fail2ban

# ### Set the system timezone
#
# Some systems are missing /etc/timezone, which we cat into the configs for
# Z-Push and ownCloud, so we need to set it to something. Daily cron tasks
# like the system backup are run at a time tied to the system timezone, so
# letting the user choose will help us identify the right time to do those
# things (i.e. late at night in whatever timezone the user actually lives
# in).
#
# However, changing the timezone once it is set seems to confuse fail2ban
# and requires restarting fail2ban (done below in the fail2ban
# section) and syslog (see #328). There might be other issues, and it's
# not likely the user will want to change this, so we only ask on first
# setup.
if [ -z "$NONINTERACTIVE" ]; then
	if [ ! -f /etc/timezone ] || [ ! -z $FIRST_TIME_SETUP ]; then
		# If the file is missing or this is the user's first time running
		# Mail-in-a-Box setup, run the interactive timezone configuration
		# tool.
		dpkg-reconfigure tzdata
		restart_service rsyslog
	fi
else
	# This is a non-interactive setup so we can't ask the user.
	# If /etc/timezone is missing, set it to UTC.
	if [ ! -f /etc/timezone ]; then
		echo "Setting timezone to UTC."
		echo "Etc/UTC" > /etc/timezone
		restart_service rsyslog
	fi
fi

# ### Seed /dev/urandom
#
# /dev/urandom is used by various components for generating random bytes for
# encryption keys and passwords:
#
# * TLS private key (see `ssl.sh`, which calls `openssl genrsa`)
# * DNSSEC signing keys (see `dns.sh`)
# * our management server's API key (via Python's os.urandom method)
# * Roundcube's SECRET_KEY (`webmail.sh`)
# * ownCloud's administrator account password (`owncloud.sh`)
#
# Why /dev/urandom? It's the same as /dev/random, except that it doesn't wait
# for a constant new stream of entropy. In practice, we only need a little
# entropy at the start to get going. After that, we can safely pull a random
# stream from /dev/urandom and not worry about how much entropy has been
# added to the stream. (http://www.2uo.de/myths-about-urandom/) So we need
# to worry about /dev/urandom being seeded properly (which is also an issue
# for /dev/random), but after that /dev/urandom is superior to /dev/random
# because it's faster and doesn't block indefinitely to wait for hardware
# entropy. Note that `openssl genrsa` even uses `/dev/urandom`, and if it's
# good enough for generating an RSA private key, it's good enough for anything
# else we may need.
#
# Now about that seeding issue....
#
# /dev/urandom is seeded from "the uninitialized contents of the pool buffers when
# the kernel starts, the startup clock time in nanosecond resolution,...and
# entropy saved across boots to a local file" as well as the order of
# execution of concurrent accesses to /dev/urandom. (Heninger et al 2012,
# https://factorable.net/weakkeys12.conference.pdf) But when memory is zeroed,
# the system clock is reset on boot, /etc/init.d/urandom has not yet run, or
# the machine is single CPU or has no concurrent accesses to /dev/urandom prior
# to this point, /dev/urandom may not be seeded well. After this, /dev/urandom
# draws from the same entropy sources as /dev/random, but it doesn't block or
# issue any warnings if no entropy is actually available. (http://www.2uo.de/myths-about-urandom/)
# Entropy might not be readily available because this machine has no user input
# devices (common on servers!) and either no hard disk or not enough IO has
# ocurred yet --- although haveged tries to mitigate this. So there's a good chance
# that accessing /dev/urandom will not be drawing from any hardware entropy and under
# a perfect-storm circumstance where the other seeds are meaningless, /dev/urandom
# may not be seeded at all.
#
# The first thing we'll do is block until we can seed /dev/urandom with enough
# hardware entropy to get going, by drawing from /dev/random. haveged makes this
# less likely to stall for very long.

echo Initializing system random number generator...
dd if=/dev/random of=/dev/urandom bs=1 count=32 2> /dev/null

# This is supposedly sufficient. But because we're not sure if hardware entropy
# is really any good on virtualized systems, we'll also seed from Ubuntu's
# pollinate servers:

pollinate  -q -r

# Between these two, we really ought to be all set.

# ### Package maintenance
#
# Allow apt to install system updates automatically every day.

cat > /etc/apt/apt.conf.d/02periodic <<EOF;
APT::Periodic::MaxAge "7";
APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Unattended-Upgrade "1";
APT::Periodic::Verbose "1";
EOF

# ### Firewall

# Various virtualized environments like Docker and some VPSs don't provide #NODOC
# a kernel that supports iptables. To avoid error-like output in these cases, #NODOC
# we skip this if the user sets DISABLE_FIREWALL=1. #NODOC
if [ -z "$DISABLE_FIREWALL" ]; then
	# Install `ufw` which provides a simple firewall configuration.
	apt_install ufw

	# Allow incoming connections to SSH.
	ufw_allow ssh;

	# ssh might be running on an alternate port. Use sshd -T to dump sshd's #NODOC
	# settings, find the port it is supposedly running on, and open that port #NODOC
	# too. #NODOC
	SSH_PORT=$(sshd -T 2>/dev/null | grep "^port " | sed "s/port //") #NODOC
	if [ ! -z "$SSH_PORT" ]; then
	if [ "$SSH_PORT" != "22" ]; then

	echo Opening alternate SSH port $SSH_PORT. #NODOC
	ufw_allow $SSH_PORT #NODOC

	fi
	fi

	ufw --force enable;
fi #NODOC

# ### Local DNS Service

# Install a local DNS server, rather than using the DNS server provided by the
# ISP's network configuration.
#
# We do this to ensure that DNS queries
# that *we* make (i.e. looking up other external domains) perform DNSSEC checks.
# We could use Google's Public DNS, but we don't want to create a dependency on
# Google per our goals of decentralization. `bind9`, as packaged for Ubuntu, has
# DNSSEC enabled by default via "dnssec-validation auto".
#
# So we'll be running `bind9` bound to 127.0.0.1 for locally-issued DNS queries
# and `nsd` bound to the public ethernet interface for remote DNS queries asking
# about our domain names. `nsd` is configured later.
#
# About the settings:
#
# * RESOLVCONF=yes will have `bind9` take over /etc/resolv.conf to tell
#   local services that DNS queries are handled on localhost.
# * Adding -4 to OPTIONS will have `bind9` not listen on IPv6 addresses
#   so that we're sure there's no conflict with nsd, our public domain
#   name server, on IPV6.
# * The listen-on directive in named.conf.options restricts `bind9` to
#   binding to the loopback interface instead of all interfaces.
apt_install bind9 resolvconf
tools/editconf.py /etc/default/bind9 \
	RESOLVCONF=yes \
	"OPTIONS=\"-u bind -4\""
if ! grep -q "listen-on " /etc/bind/named.conf.options; then
	# Add a listen-on directive if it doesn't exist inside the options block.
	sed -i "s/^}/\n\tlisten-on { 127.0.0.1; };\n}/" /etc/bind/named.conf.options
fi
if [ -f /etc/resolvconf/resolv.conf.d/original ]; then
	echo "Archiving old resolv.conf (was /etc/resolvconf/resolv.conf.d/original, now /etc/resolvconf/resolv.conf.original)." #NODOC
	mv /etc/resolvconf/resolv.conf.d/original /etc/resolvconf/resolv.conf.original #NODOC
fi

# Restart the DNS services.

restart_service bind9
restart_service resolvconf

# ### Fail2Ban Service

# Configure the Fail2Ban installation to prevent dumb bruce-force attacks against dovecot, postfix and ssh
cat conf/fail2ban/jail.local \
	| sed "s/PUBLIC_IP/$PUBLIC_IP/g" \
	> /etc/fail2ban/jail.local
cp conf/fail2ban/dovecotimap.conf /etc/fail2ban/filter.d/dovecotimap.conf

restart_service fail2ban