A small Linux patch collection called Grsecurity (for Greater Security) [1] transforms the Linux kernel into an extremely untrusting fellow. Grsecurity unleashes a whole package of actions that preemptively block out attackers. Each user is initially treated as a principal source of danger. For example, Grsecurity only allows certain users to call dmesg; it locks the /proc directory, and it prevents access to /dev/kmem, /dev/mem, and /dev/port. Grsecurity also moves applications to a random location in memory (address space layout randomization), and it hides all the kernel threads.

Role-Play

The core of Grsecurity is Role-Based Access Control (RBAC for short), which sits on top of existing rights management. Grsecurity initially deprives all users of their access rights, even hiding parts of the filesystem from them, and thus allows only the bare necessities. The administrator can then allow specific actions for individual users. Users with similar tasks can be grouped as "roles," and the admin can then grant additional rights to these roles. For example, the webmaster group needs to start the SSH daemon, but the database administrator group does not.

The configuration is very easy: Just let Grsecurity watch the webmaster work for a while and then allow the actions the webmaster performed. All other actions remain forbidden. Of course, you can still manually refine or adapt this automatically determined configuration.

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