Patch Lion HomeDirMechanism Format Strings with Null Bytes and Purge Security Logs

patchhomedirmech.rb

#!/usr/bin/ruby
# This code comes with no guarantees and it is not a "fix", just a workaround.
# It would be trivial to replace the patched file and restore these debugging messages.
# Also, this script modifies a Mac OS X System file, so...

require 'etc'
require 'fileutils'
require 'syslog'

@log          = Syslog.open('patchhomedirmech')
@target       = '/System/Library/CoreServices/SecurityAgentPlugins/HomeDirMechanism.bundle/Contents/MacOS/HomeDirMechanism'
@backup_file  = '/private/var/root/HomeDirMechanism.backup'
@newfile_path = '/private/var/root/HomeDirMechanism.new'

def our_rescue(msg)
  @log.notice(msg)
  @log.close
  exit 1
end

#####################################################################
# => MAIN
#####################################################################

# Check UID (must be root)
unless Process.euid == 0
  raise "You must be root to execute this script."
end

begin
  @log.notice("Backing up file: #{@target}")
  FileUtils.cp(@target, @backup_file)
rescue => e
  our_rescue("Error backing up file: #{e.message}")
end
 
@debug_strings = `/usr/bin/strings #{@target} | /usr/bin/grep "password.* = %s" 2> /dev/null`

if @debug_strings
  @debug_strings = @debug_strings.split("\n")
else
  our_rescue("Nothing to patch: target does not contain any relevant debugging strings")
end

begin
  @file    = File.read(@target)
  @newfile = File.new(@newfile_path, 'w')
rescue => e
  our_rescue("Error loading file: #{e.message}")
end  
  
begin
  @log.notice("Patching file: #{@newfile_path}")
  @debug_strings.each do |string|
    len = string.length
    replacement = ''
    len.times { replacement << "\000" }
    @file.gsub!(string, replacement)
  end
  @newfile << @file
  @newfile.flush
  @newfile.close
rescue => e
  our_rescue("Error patching file: #{e.message}")
end

begin
  @log.notice("Replacing file: #{@target}")
  FileUtils.rm_rf(@target)
  FileUtils.move(@newfile_path, @target)
rescue => e
  our_rescue("Error replacing file: #{e.message}")
end

begin
  @log.notice("Nullfying security logs...")
  raise unless system("cat /dev/null > /var/log/secure.log")
  @log.notice("Removing archived security logs...")
  logs = Dir.glob("/private/var/log/secure*.bz2")
  logs.each { |log| FileUtils.rm(log) }
rescue => e
  our_rescue("Error deleting log(s): #{e.message}")
end

@log.notice("Done.")

@log.close
exit 0