#!/bin/sh -e

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

. /usr/share/debconf/confmodule
db_version 2.0

umask 022

if [ "$action" != configure ]
  then
  exit 0
fi


fix_doc_symlink() {
	if [ ! -L /usr/share/doc/openssh-server ] && \
	   dpkg --compare-versions "$oldversion" lt-nl 1:4.1p1-5; then
		rm -rf /usr/share/doc/openssh-server
		ln -s openssh-client /usr/share/doc/openssh-server
	fi
}

check_idea_key() {
	# check for old host_key files using IDEA, which openssh does not
	# support
	if [ -f /etc/ssh/ssh_host_key ] ; then
		cp -a /etc/ssh/ssh_host_key /etc/ssh/ssh_host_key.check_idea
		if ssh-keygen -p -N '' -f /etc/ssh/ssh_host_key.check_idea 2>&1 | \
				grep -q 'unknown cipher' 2>/dev/null; then
			mv /etc/ssh/ssh_host_key /etc/ssh/ssh_host_key.old
			mv /etc/ssh/ssh_host_key.pub /etc/ssh/ssh_host_key.pub.old
		fi
		rm -f /etc/ssh/ssh_host_key.check_idea
	fi
}


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
}


disable_config_option() {
	option="$1"

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

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


remove_obsolete_gssapi() {
	disable_config_option GSSAPINoMICAuthentication
	disable_config_option GSSUseSessionCCache
	disable_config_option GSSAPIUseSessionCredCache
}


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
		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.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
}


vulnerable_host_keys() {
	# If the admin has explicitly put the vulnerable keys back, we
	# assume they can look after themselves.
	db_fget ssh/vulnerable_host_keys seen
	if [ "$RET" = true ]; then
		return 0
	fi

	hostkeys="$(host_keys_required)"
	vulnerable=
	for hostkey in $hostkeys; do
		[ -f "$hostkey" ] || continue
		if ssh-vulnkey -q "$hostkey"; then
			vulnerable="${vulnerable:+$vulnerable }$hostkey"
		fi
	done
	if [ "$vulnerable" ]; then
		db_subst ssh/vulnerable_host_keys HOST_KEYS "$vulnerable"
		db_input critical ssh/vulnerable_host_keys || true
		db_go
		for hostkey in $vulnerable; do
			mv "$hostkey" "$hostkey.broken" || true
			mv "$hostkey.pub" "$hostkey.pub.broken" || true
		done
		create_keys
	fi
}


check_password_auth() {
	passwordauth="$(get_config_option PasswordAuthentication)"
	crauth="$(get_config_option ChallengeResponseAuthentication)"
	if [ "$passwordauth" = no ] && \
	   ([ -z "$crauth" ] || [ "$crauth" = yes ]); then
		db_get ssh/disable_cr_auth
		if [ "$RET" = true ]; then
			set_config_option ChallengeResponseAuthentication no
		fi
	fi
}


move_subsystem_sftp() {
	subsystem_sftp="$(get_config_option 'Subsystem sftp')"
	if [ "$subsystem_sftp" = /usr/lib/sftp-server ] || \
	   [ "$subsystem_sftp" = /usr/libexec/sftp-server ]; then
		set_config_option 'Subsystem sftp' /usr/lib/openssh/sftp-server
	fi
}


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

	    if (dpkg --compare-versions "$oldversion" lt-nl 1:3.8p1-1 && \
		! grep -iq ^UsePAM /etc/ssh/sshd_config) || \
	       grep -Eiq '^(PAMAuthenticationViaKbdInt|RhostsAuthentication)' \
		 /etc/ssh/sshd_config ; then
		# Upgrade from pre-3.7: UsePAM needed to maintain standard
		# Debian configuration.
		# Note that --compare-versions is sadly not reliable enough
		# here due to the package split of ssh into openssh-client
		# and openssh-server. The extra grep for some deprecated
		# options should with any luck be a good enough heuristic.
		echo -n 'Upgrading sshd_config (old version in .dpkg-old) ...'
		cp -a /etc/ssh/sshd_config /etc/ssh/sshd_config.dpkg-old
		perl -pe 's/^(PAMAuthenticationViaKbdInt|RhostsAuthentication)\b/#$1/i' \
		    /etc/ssh/sshd_config > /etc/ssh/sshd_config.dpkg-new
		echo >> /etc/ssh/sshd_config.dpkg-new
		echo 'UsePAM yes' >> /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
		echo
	    fi

	    # An empty version means we're upgrading from before the
	    # package split, so check.
	    if dpkg --compare-versions "$oldversion" lt 1:3.8.1p1-11; then
		check_password_auth
	    fi

	    # libexecdir changed, so fix up 'Subsystem sftp'.
	    if dpkg --compare-versions "$oldversion" lt 1:4.1p1-1; then
		move_subsystem_sftp
	    fi

	    # Remove obsolete GSSAPI options.
	    if dpkg --compare-versions "$oldversion" lt 1:4.3p2-8; then
		remove_obsolete_gssapi
	    fi

	    # 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

	    return 0
	fi

	#Preserve old sshd_config before generating a new one
	if [ -e /etc/ssh/sshd_config ] ; then 
	    mv /etc/ssh/sshd_config /etc/ssh/sshd_config.dpkg-old
	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
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes

# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 768

# 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
}

fix_sshd_shell() {
	if getent passwd sshd | grep -q ':/bin/false$'; then
		usermod -s /usr/sbin/nologin sshd || true
	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
}

fix_conffile_permissions() {
	# Clean up after executable /etc/default/ssh in 1:3.5p1-5. dpkg
	# doesn't do this for us; see bug #192981.
	chmod 644 /etc/default/ssh
}

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
}

setup_init() {
	if [ -x /etc/init.d/ssh ]; then
		update-rc.d ssh start 16 2 3 4 5 . >/dev/null
		if [ -x /usr/sbin/invoke-rc.d ]; then
			invoke-rc.d ssh restart
		else
			/etc/init.d/ssh restart
		fi
	fi
}

commit_transfer_conffile () {
	CONFFILE="$1"
	if [ -e "$CONFFILE.moved-by-preinst" ]; then
		rm -f "$CONFFILE.moved-by-preinst"
	fi
}

commit_mv_conffile () {
	OLDCONFFILE="$1"
	NEWCONFFILE="$2"

	if [ -e "$OLDCONFFILE.moving" ]; then
		echo "Preserving user changes to $NEWCONFFILE ..."
		mv -f "$NEWCONFFILE" "$NEWCONFFILE.dpkg-new"
		mv -f "$OLDCONFFILE.moving" "$NEWCONFFILE"
	elif [ -e "$OLDCONFFILE.dpkg-old" ]; then
		rm -f "$OLDCONFFILE.dpkg-old"
	fi
}


fix_doc_symlink
create_sshdconfig
check_idea_key
create_keys
vulnerable_host_keys
fix_statoverride
if dpkg --compare-versions "$2" lt 1:4.3p2-3; then
    fix_sshd_shell
fi
setup_sshd_user
if dpkg --compare-versions "$2" lt 1:3.6.1p2-2; then
    fix_conffile_permissions
fi
if dpkg --compare-versions "$2" lt 1:5.2p1-1; then
    remove_old_init_links
fi
setup_init
commit_transfer_conffile /etc/default/ssh
commit_transfer_conffile /etc/init.d/ssh
commit_transfer_conffile /etc/pam.d/ssh
commit_mv_conffile /etc/pam.d/ssh /etc/pam.d/sshd
# 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


db_stop

exit 0