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Console Debugging

Warning:  Failure to follow this advice can unintentionally expose security-critical information.

In traditional UNIX and UNIX-like systems, the console is owned by root. Only root sees console messages. For this reason, print statements in the kernel are relatively secure.

In Mac OS X, any user can run the Console application. This represents a major departure from other UNIX-like systems. While it is never a good idea to include sensitive information in kernel debugging statements, it is particularly important not to do so in Mac OS X. You must assume that any information displayed to the console could potentially be read by any user on the system (since the console is virtualized in the form of a user-viewable window).

Printing any information involving sensitive data, including its location on disk or in memory, represents a security hole, however slight, and you should write your code accordingly. Obviously this is of less concern if that information is only printed when the user sets a debugging flag somewhere, but for normal use, printing potentially private information to the console is strongly discouraged.

You must also be careful not to inadvertently print information that you use for generating password hashes or encryption keys, such as seed values passed to a random number generator.

This is, by necessity, not a complete list of information to avoid printing to the console. You must use your own judgement when deciding whether a piece of information could be valuable if seen by a third party, and then decide if it is appropriate to print it to the console.

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