#!/bin/sh
set -e

action="$1"
oldversion="$2"

umask 022


get_config_option() {
	option="$1"

	[ -f /etc/ssh/sshd_config ] || return

	# TODO: actually only one '=' allowed after option
	perl -lne 's/\s+/ /g; print if s/^\s*'"$option"'[[:space:]=]+//i' \
	   /etc/ssh/sshd_config
}


set_config_option() {
	option="$1"
	value="$2"

	perl -le '
		$option = $ARGV[0]; $value = $ARGV[1]; $done = 0;
		while (<STDIN>) {
			chomp;
			(my $match = $_) =~ s/\s+/ /g;
			if ($match =~ s/^\s*\Q$option\E\s+.*/$option $value/) {
				$_ = $match;
				$done = 1;
			}
			print;
		}
		print "$option $value" unless $done;' \
		"$option" "$value" \
		< /etc/ssh/sshd_config > /etc/ssh/sshd_config.dpkg-new
	chown --reference /etc/ssh/sshd_config /etc/ssh/sshd_config.dpkg-new
	chmod --reference /etc/ssh/sshd_config /etc/ssh/sshd_config.dpkg-new
	mv /etc/ssh/sshd_config.dpkg-new /etc/ssh/sshd_config
}


rename_config_option() {
	oldoption="$1"
	newoption="$2"

	value="$(get_config_option "$oldoption")"
	[ "$value" ] || return 0

	perl -le '
		$oldoption = $ARGV[0]; $newoption = $ARGV[1];
		while (<STDIN>) {
			chomp;
			(my $match = $_) =~ s/\s+/ /g;
			# TODO: actually only one "=" allowed after option
			if ($match =~ s/^(\s*)\Q$oldoption\E([[:space:]=]+)/$1$newoption$2/i) {
				$_ = $match;
			}
			print;
		}' \
		"$oldoption" "$newoption" \
		< /etc/ssh/sshd_config > /etc/ssh/sshd_config.dpkg-new
	chown --reference /etc/ssh/sshd_config /etc/ssh/sshd_config.dpkg-new
	chmod --reference /etc/ssh/sshd_config /etc/ssh/sshd_config.dpkg-new
	mv /etc/ssh/sshd_config.dpkg-new /etc/ssh/sshd_config
}


host_keys_required() {
	hostkeys="$(get_config_option HostKey)"
	if [ "$hostkeys" ]; then
		echo "$hostkeys"
	else
		# No HostKey directives at all, so the server picks some
		# defaults depending on the setting of Protocol.
		protocol="$(get_config_option Protocol)"
		[ "$protocol" ] || protocol=1,2
		if echo "$protocol" | grep 1 >/dev/null; then
			echo /etc/ssh/ssh_host_key
		fi
		if echo "$protocol" | grep 2 >/dev/null; then
			echo /etc/ssh/ssh_host_rsa_key
			echo /etc/ssh/ssh_host_dsa_key
			echo /etc/ssh/ssh_host_ecdsa_key
			echo /etc/ssh/ssh_host_ed25519_key
		fi
	fi
}


create_key() {
	msg="$1"
	shift
	hostkeys="$1"
	shift
	file="$1"
	shift

	if echo "$hostkeys" | grep -x "$file" >/dev/null && \
	   [ ! -f "$file" ] ; then
		echo -n $msg
		ssh-keygen -q -f "$file" -N '' "$@"
		echo
		if which restorecon >/dev/null 2>&1; then
			restorecon "$file" "$file.pub"
		fi
	fi
}


create_keys() {
	hostkeys="$(host_keys_required)"

	create_key "Creating SSH1 key; this may take some time ..." \
		"$hostkeys" /etc/ssh/ssh_host_key -t rsa1

	create_key "Creating SSH2 RSA key; this may take some time ..." \
		"$hostkeys" /etc/ssh/ssh_host_rsa_key -t rsa
	create_key "Creating SSH2 DSA key; this may take some time ..." \
		"$hostkeys" /etc/ssh/ssh_host_dsa_key -t dsa
	create_key "Creating SSH2 ECDSA key; this may take some time ..." \
		"$hostkeys" /etc/ssh/ssh_host_ecdsa_key -t ecdsa
	create_key "Creating SSH2 ED25519 key; this may take some time ..." \
		"$hostkeys" /etc/ssh/ssh_host_ed25519_key -t ed25519
}


fix_loglevel_silent() {
	if [ "$(get_config_option LogLevel)" = SILENT ]; then
		set_config_option LogLevel QUIET
	fi
}


update_server_key_bits() {
	if [ "$(get_config_option ServerKeyBits)" = 768 ]; then
		set_config_option ServerKeyBits 1024
	fi
}


create_sshdconfig() {
	if [ -e /etc/ssh/sshd_config ] ; then
	    # Upgrade an existing sshd configuration.

	    # This option was renamed in 3.8p1, but we never took care
	    # of adjusting the configuration file until now.
	    if dpkg --compare-versions "$oldversion" lt 1:4.7p1-8; then
		rename_config_option KeepAlive TCPKeepAlive
	    fi

	    # 'LogLevel SILENT' is now equivalent to QUIET.
	    if dpkg --compare-versions "$oldversion" lt 1:5.4p1-1; then
		fix_loglevel_silent
	    fi

	    # Changed upstream in 5.1p1, but we forgot to update the
	    # package-generated configuration file until now.
	    if dpkg --compare-versions "$oldversion" lt 1:6.4p1-2; then
		update_server_key_bits
	    fi

	    return 0
	fi

	cat <<EOF > /etc/ssh/sshd_config
# Package generated configuration file
# See the sshd_config(5) manpage for details

# What ports, IPs and protocols we listen for
Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#ListenAddress ::
#ListenAddress 0.0.0.0
Protocol 2
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes

# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 1024

# Logging
SyslogFacility AUTH
LogLevel INFO

# Authentication:
LoginGraceTime 120
PermitRootLogin yes
StrictModes yes

RSAAuthentication yes
PubkeyAuthentication yes
#AuthorizedKeysFile	%h/.ssh/authorized_keys

# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes

# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no

# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no

# Change to no to disable tunnelled clear text passwords
#PasswordAuthentication yes

# Kerberos options
#KerberosAuthentication no
#KerberosGetAFSToken no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no

#MaxStartups 10:30:60
#Banner /etc/issue.net

# Allow client to pass locale environment variables
AcceptEnv LANG LC_*

Subsystem sftp /usr/lib/openssh/sftp-server

# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication.  Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
UsePAM yes
EOF
}

fix_statoverride() {
# Remove an erronous override for sshd (we should have overridden ssh)
	if [ -x /usr/sbin/dpkg-statoverride ]; then
		if dpkg-statoverride --list /usr/sbin/sshd >/dev/null ; then
			dpkg-statoverride --remove /usr/sbin/sshd
		fi
	fi
}

setup_sshd_user() {
	if ! getent passwd sshd >/dev/null; then
		adduser --quiet --system --no-create-home --home /var/run/sshd --shell /usr/sbin/nologin sshd
	fi
}

remove_old_init_links() {
	# Yes, this only works with the SysV init script layout. I know.
	# The important thing is that it doesn't actually *break* with
	# file-rc ...
	if [ -e /etc/rc2.d/S20ssh ]; then
		update-rc.d -f ssh remove >/dev/null 2>&1
	fi
	rm -f /etc/rc0.d/K??ssh /etc/rc1.d/K??ssh /etc/rc6.d/K??ssh
}

if [ "$action" = configure ]; then
	create_sshdconfig
	create_keys
	fix_statoverride
	setup_sshd_user
	if dpkg --compare-versions "$2" lt 1:5.2p1-1; then
	    remove_old_init_links
	fi
	# Renamed to /etc/ssh/moduli in 2.9.9 (!)
	if dpkg --compare-versions "$2" lt 1:4.7p1-1; then
	    rm -f /etc/ssh/primes
	fi
	if dpkg --compare-versions "$2" lt 1:5.5p1-6; then
	    rm -f /var/run/sshd/.placeholder
	fi
	if dpkg --compare-versions "$2" lt 1:6.2p2-3 && \
	   which initctl >/dev/null && initctl version | grep -q upstart && \
	   ! status ssh 2>/dev/null | grep -q ' start/'; then
	    # We must stop the sysvinit-controlled sshd before we can
	    # restart it under Upstart.
	    start-stop-daemon --stop --quiet --oknodo --pidfile /var/run/sshd.pid || true
	fi
	if dpkg --compare-versions "$2" lt 1:6.5p1-2 && \
	   deb-systemd-helper debian-installed ssh.socket && \
	   deb-systemd-helper --quiet was-enabled ssh.service && \
	   deb-systemd-helper --quiet was-enabled ssh.socket; then
	    # 1:6.5p1-1 mistakenly left both ssh.service and ssh.socket
	    # enabled.
	    deb-systemd-helper disable ssh.socket >/dev/null || true
	fi
	if dpkg --compare-versions "$2" lt 1:6.5p1-3 && \
	   [ -d /run/systemd/system ]; then
	    # We must stop the sysvinit-controlled sshd before we can
	    # restart it under systemd.
	    start-stop-daemon --stop --quiet --oknodo --pidfile /var/run/sshd.pid --exec /usr/sbin/sshd || true
	fi
fi

#DEBHELPER#

exit 0