This post describes how to encrypt the home directory of your users on GNU Linux with the help of TrueCrypt and PAM using the login-password as encryption key. I wrote about Automatic encryption of home directories using TrueCrypt before. This time we'll use TrueCrypt 6.0a which is a bit different from 4.3a used last time. Futhermore we'll use Ubuntu 8.04 Hardy Heron instead of Debian Etch. For convenience this post will be selfcontained (ie. I copy redundant parts from the old one).
The String#constantize method is a feature that makes rails fun to code with. This method converts a string to the constant that the string contains (or throws a NameError if there is no such constant). It makes it easy to store class-types in databases as strings and to code controllers that work with classes of the same duck type. Most people know that eval on user data is dangerous, but noboddy seems to care about constantize. Beware, it is also dangerous and you should constantize with care!
I recently found a shell injection bug in some Ruby-gem I use. Shell injections have scared me for a long time and I usually prefer to whitelist certain characters/patterns rather than to blacklist. This means that the system fails to the save side. Unfortunally it usually does fail – my whitelisting is to rigorous and data that would not cause any problems gets rejected. So I decided to take the opportunity to investigate how to prevent shell injection in my favorite scripting language (Python), the language I found the problem in and finally the language that I can not avoid (PHP).