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Securing Debian Manual
Appendix E - Sample script to change the default Bind installation.


This script automates the procedure of changing the name server's default installation so that it does not run as the superuser. Use with extreme care since it has not been tested thoroughly. The script will create the user and groups to be used for the name server.

     #!/bin/sh
     # Change the default Debian bind configuration to have it run
     # with a non-root user and group.
     #
     # WARN: This script has not been tested throughly, please
     # verify the changes made to the INITD script
     
     # (c) 2002 Javier Fernandez-Sanguino Peña
     #
     #    This program is free software; you can redistribute it and/or modify
     #    it under the terms of the GNU General Public License as published by
     #    the Free Software Foundation; either version 1, or (at your option)
     #    any later version.
     #
     #    This program is distributed in the hope that it will be useful,
     #    but WITHOUT ANY WARRANTY; without even the implied warranty of
     #    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     #    GNU General Public License for more details.
     #
     #     Please see the file `COPYING' for the complete copyright notice.
     #
     
     restore() {
     # Just in case, restore the system if the changes fail
     	echo "WARN: Restoring to the previous setup since I'm unable to properly change it."
     	echo "WARN: Please check the $INITDERR script."
     	mv $INITD $INITDERR
     	cp $INITDBAK $INITD
     }
     
     
     USER=named
     GROUP=named
     INITD=/etc/init.d/bind
     INITDBAK=$INITD.preuserchange
     INITDERR=$INITD.changeerror
     START="start-stop-daemon --start --quiet --exec /usr/sbin/named -- -g $GROUP -u $USER"
     AWKS="awk ' /start-stop-daemon --start/ { print \"$START\"; noprint = 1; }; /\/usr\/sbin\/ndc reload/ { print \"stop; sleep 2; start;\"; noprint = 1; } /\\\\$/ { if ( noprint != 0 ) { noprint = noprint + 1;} } /^.*$/ { if ( noprint != 0 ) { noprint = noprint - 1; } else { print \$0; } } '"
     
     [ `id -u` -ne 0 ] && {
     	echo "This program must be run by the root user"
     	exit 1
     }
     
     RUNUSER=`ps -eo user,fname |grep named |cut -f 1 -d " "`
     
     if [ "$RUNUSER" = "$USER" ] 
     then
     	echo "WARN: The name server running daemon is already running as $USER"
     	echo "ERR:  This script will not many any changes to your setup."
     	exit 1
     fi
     if [ ! -f $INITD ]
     then
             echo "ERR:  This system does not have $INITD (which this script tries to change)"
             RUNNING=`ps -eo fname |grep named`
              [ -z "$RUNNING" ] && \
     	    echo "ERR:  In fact the name server daemon is not even running (is it installed?)"
              echo "ERR:  No changes will be made to your system"
     	exit 1
     fi
     
     # Check if named group exists
     if [ -z "`grep $GROUP /etc/group`" ] 
     then
     	echo "Creating group $GROUP:"
     	addgroup $GROUP
     else
     	echo "WARN: Group $GROUP already exists. Will not create it"
     fi
     # Same for the user
     if [ -z "`grep $USER /etc/passwd`" ] 
     then
     	echo "Creating user $USER:"
     	adduser --system --home /home/$USER \
     	--no-create-home --ingroup $GROUP \
     	--disabled-password --disabled-login $USER
     else
     	echo "WARN: The user $USER already exists. Will not create it"
     fi
     
     # Change the init.d script
     
     # First make a backup (check that there is not already
     # one there first)
     if [ ! -f $INITDBAK ] 
     then
     	cp $INITD $INITDBAK
     fi
     
     # Then use it to change it
     cat $INITDBAK |
     eval $AWKS > $INITD
     
     echo "WARN: The script $INITD has been changed, trying to test the changes."
     echo "Restarting the named daemon (check for errors here)."
     
     $INITD restart
     if [ $? -ne 0 ] 
     then
     	echo "ERR:  Failed to restart the daemon."
     	restore
     	exit 1
     fi
     
     RUNNING=`ps -eo fname |grep named`
     if [ -z "$RUNNING" ] 
     then
     	echo "ERR:  Named is not running, probably due to a problem with the changes."
     	restore
     	exit 1
     fi
     
     # Check if it's running as expected
     RUNUSER=`ps -eo user,fname |grep named |cut -f 1 -d " "`
     
     if [ "$RUNUSER" = "$USER" ] 
     then
     	echo "All has gone well, named seems to be running now as $USER."
     else
     	echo "ERR:  The script failed to automatically change the system."
     	echo "ERR:  Named is currently running as $RUNUSER."
     	restore
     	exit 1
     fi
     
     exit 0

The previous script, run on woody's (Debian 3.0) custom's bind will produce the following initd file after creating the 'named' user and group:

     #!/bin/sh
     
     PATH=/sbin:/bin:/usr/sbin:/usr/bin
     
     test -x /usr/sbin/named || exit 0
     
     start () {
     	echo -n "Starting domain name service: named"
     	start-stop-daemon --start --quiet \
     	    --pidfile /var/run/named.pid --exec /usr/sbin/named 
     	echo "."	
     }
     
     stop () {
     	echo -n "Stopping domain name service: named"
     	# --exec doesn't catch daemons running deleted instances of named,
     	# as in an upgrade.  Fortunately, --pidfile is only going to hit
     	# things from the pidfile.
     	start-stop-daemon --stop --quiet  \
     	    --pidfile /var/run/named.pid --name named
     	echo "."	
     }
     
     case "$1" in
         start)
     	start
         ;;
     
         stop)
     	stop
         ;;
     
         restart|force-reload)
     	stop
     	sleep 2
     	start
         ;;
         
         reload)
     	/usr/sbin/ndc reload
         ;;
     
         *)
     	echo "Usage: /etc/init.d/bind {start|stop|reload|restart|force-reload}" >&2
     	exit 1
         ;;
     esac
     
     exit 0

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Securing Debian Manual

2.5 (beta) 29 augusti 2002Sat, 17 Aug 2002 12:23:36 +0200
Javier Fernández-Sanguino Peña jfs@computer.org