Host changeover.

[firewall] / prologue.m4

### -*-sh-*-
###
### Failsafe prologue for firewall scripts
###
### (c) 2008 Mark Wooding
###

###----- Licensing notice ---------------------------------------------------
###
### 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 2 of the License, 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.
###
### You should have received a copy of the GNU General Public License
### along with this program; if not, write to the Free Software Foundation,
### Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

m4_divert(10)m4_dnl
###--------------------------------------------------------------------------
### Failsafe prologue.

revert () {
  escape=$1 badness=$2
  ## Report a firewall script failure and retreat to a safe place.

  echo "$2!  Retreating to safe version..."
  if ! "$1" revert; then
    echo >&2 "Safe firewall failed.  You're screwed.  Good luck."
    exit 1
  fi
  echo >&2 "Phew!  Fallback to safe version successful."
  exit 1
}

finished () {
  echo "Done."
  exit 0
}

try () {
  old=$1 new=$2
  ## Install the NEW firewall rules.  If it fails, revert to the OLD ones.
  ## Updating firewall rules can fail spectacularly, so be careful.  Leave a
  ## timebomb in the form of NEW.errors: if this isn't removed in 10 seconds
  ## after the NEW rules complete successfully, then revert.  Write errors to
  ## NEW.errors.

  ## Make sure we have an escape route.
  if [ ! -x "$old" ]; then
    echo >&2 "$0: no escape plan: \`$old' is missing"
    exit 1
  fi

  ## Clear the air and make the errors file.
  rm -f "$new.errors" "$new.timebomb" "$new.grabbed"
  exec >"$new.errors" 2>&1

  ## Now try to install the new firewall.
  "$new" install || revert "$old" "Failed"

  ## Set up the time bomb.  Leave the errors file there if we failed.
  (sleep 10
   if [ -f "$new.errors" ]; then
     mv "$new.errors" "$new.timebomb"
     revert "$old" "Time bomb"
   fi)&
}

catch () {
  new=$1
  ## Report successful installation of the script.

  if mv "$new.errors" "$new.grabbed" 2>/dev/null; then
    rc=0
    echo "Installed OK."
  else
    mv "$new.timebomb" "$new.grabbed"
    echo "Timebomb went off."
    rc=1
  fi
  cat "$new.grabbed" >&2
  rm -f "$new.grabbed"
  return $rc
}

exit_after_clearing=:
export FWCOOKIE=magical
case "$#,${1-update}" in
  1,start | 1,restart | 1,reload | 1,force-reload)
    echo -n "Starting up firewall... "
    "$firewall_script" install || revert "$firewall_failsafe" "Failed"
    finished
    ;;
  1,stop)
    echo -n "Shutting down firewall... "
    exit_after_clearing=finished
    ;;
  1,replace | 1,test)
    echo -n "Running new firewall... "
    if ! (try "$firewall_script" "$0"); then
      echo "FAILED."
      cat "$0.errors" >&2
      exit
    fi
    echo "done."
    echo "Can you hear me?"
    (trap 'exit 127' TERM
     while :; do
       if [ -f "$0.timebomb" ]; then
	 kill $$
	 echo "Timebomb went off!"
	 cat "$0.timebomb"
	 exit 1
       fi
       sleep 1
     done)&
    read answer
    kill $!
    catch "$0"
    case "$1,$answer" in
      replace,y* | replace,Y*)
	install -m755 "$0" "$firewall_script"
	echo "Cool.  Firewall script replaced."
	exit 0
	;;
      test,y* | test,Y*)
	echo "Cool.  Everything seems good."
	exit 0
	;;
      *)
	revert "$firewall_script" "Bogus"
	;;
    esac
    ;;
  1,remote-prepare)
    try "$firewall_script" "$0"
    exit 0
    ;;
  1,remote-commit)
    catch "$0"
    install -m755 "$0" "$firewall_script"
    exit 0
    ;;
  1,install | 1,revert)
    ;;
  *)
    cat >&2 <<EOF
Usage:
	$0 start|stop|reload|restart|force-reload
	$0 replace|test|remote-prepare|remote-commit
EOF
    exit 1
    ;;
esac

m4_divert(-1)
###----- That's all, folks --------------------------------------------------