#! /bin/sh
# rcontrol (Bourne shell script) -- execute one of a list of permitted actions on a remote host
# This script is designed to have other hard links like "rshutdown".
# Note: the list is enforced by the remote host, using a grep-based filter
# (in ~root/.authorized_keys) that only allows certain commands to be executed.
# Separate passphraseless SSH keys are used for each host.  The remote host's
# root account is used (therefore "PermitRootLogin without-password" is needed
# in sshd_config; it is strongly recommended that this not be set to "yes").
#
# Usage: {rshutdown|rreboot|rpoweroff} [ -i <keyfile> ] <hostname>
#     or rcontrol -g [ -i <keyfile> ] <hostname>
#     or rcontrol -e [ -i <keyfile> ] <hostname>
# Options
#   -e  output the line to be added to .authorized_keys on <hostname>
#   -g  generate a new key and save it, and also output a line like -e
#
# Limitations:
# Due to the security-related restriction that all permissible commands must be
# listed in .authorized_keys, a shutdown delay is not supported.
# TO-DO: overcome this limitation using a regular expression (grep is already being used!)
#
# Installation (Bourne shell):
# for cmd in rshutdown rreboot rpoweroff ; do ln rcontrol $cmd ; done
#
# Installation (C shell):
# foreach cmd (rshutdown rreboot rpoweroff)
#   ln rcontrol $cmd
# end
#
# See Also:
# http://www.voipphreak.ca/2007/10/22/shutdown-linux-from-windows-remotely-using-ssh-host-keys/
# is an independently-developed tool using a similar mechanism.
#
# Version: 1.0.2

self=`basename $0`
allowed_options=i:ge

# Handle link name
# (this sets the command to be run, and/or adds extra options applicable to the
# value of $self)
case $self in
  rshutdown) command='shutdown now';;    # to single-user mode
  rreboot) command='shutdown -r now';;
  rpoweroff) command='shutdown -h now';;
  rcontrol) allowed_options=ge$allowed_options;;
  *) echo 'rcontrol: invoked through unknown name' >&2; exit 6;;
esac

# process options
set -- `getopt +$allowed_options "$@"`
while [ x$1 != x-- ] ; do
  case $1 in
    -e) action=show_auth_entries ;;
    -g) action=generate ;;
    -i) keyfile=$2
        shift         # get rid of the option
        ;;
  esac
  shift       # get rid of the option (or its arg if the inner shift already got rid it)
done
shift       # get rid of the "--"

# process the remaining (non-option) arguments
if [ -z "$1" ] ; then
  echo "${self}: host name not provided" >&2
  exit 7
else
  host=$1
  shift

  if [ -z $keyfile ] ; then
    keyfile=$HOME/Hosts/$host/ssh_control_key
  fi

  # take one of the three main actions
  if [ -z "$action" ] ; then
    if [ -z "$command" ] ; then
      echo 'rcontrol: named actions not supported' >&2
      exit 5
    fi

    if [ -r "$keyfile" ] ; then
      # when no named action is specified, log into the remote host and perform the command
      # (the command given in the .authorized_keys file will be executed instead of 'fake_command')
      echo "$command" | ssh -i $keyfile root@$host fake_command
    else
      echo "$self: key file not found ($keyfile)" >&2
      exit 10
    fi
  else
    if [ $action = generate ] ; then
      # generate per-host passphraseless key
      ssh-keygen -t dsa -f $keyfile -N '' -C "control key for $host"
    fi

    # ASSERT: action is 'show_auth_entries' or something (e.g. 'generate')
    #         that does the same thing during operation
    ## if expr "$2" : ".*\.pub" ; then
    ##   ID_FILE="$2"
    ## else
    ##   ID_FILE="$2.pub"
    ## fi


    if [ -r "$keyfile.pub" ] ; then
      # (this happens for all actions)
      # Now output the necessary record to be placed into .authorized_keys,
      # containing a forced-command spec (see sshd(8)) and a public key.
      # The command in this spec is the grep-based filter mentioned above.
      #
      # The record consists of the following literal* text:
      #     command="grep -e '^<cmd_a>$' -e '^<cmd_b>$' | sh" <pubkey>
      # * text in angle-brackets represents data generated by this script
      echo -n command='"grep ' 
      for cmd in 'shutdown now' 'shutdown -r now' 'shutdown -h now'; do
        echo -n "-e '^$cmd$' "
      done
      echo -n ' | sh" '
      cat $keyfile.pub 
    else
      echo "$self: public key file not found ($keyfile.pub)" >&2
      exit 11
    fi
  fi
fi