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


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

       #!/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 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

2.99 18 April 2004Wed, 3 Mar 2004 09:18:54 +0100

Javier Fernández-Sanguino Peña jfs@computer.org