Security is more than bug fixing. Security fixing/updating, the thing most people are exposed to, is “reactive security”. However, a large area of security work is “proactive” where defensive abilities are put in place to try and catch problems before they happen, or make classes of vulnerabilities unexploitable. This kind of security is what a lot of people don’t understand, and I think it’s important to point out so the distinction can be clearly seen.
In the Linux kernel, there’s yet another distinction: userspace proactive security and kernel proactive security. Most of the effort in kernel code has been protecting userspace from itself (things like Address Space Layout Randomization), but less attention has been given to protecting the kernel from userspace (currently if a serious enough flaw is found in the kernel, it is usually very easy to exploit it).
One project has taken great strides with proactive security for the Linux kernel: PaX and grsecurity. There hasn’t been a concerted effort to get its pieces upstream and it’s long overdue. People are starting to take proactive kernel security more seriously, though there is still plenty of debate.
© 2010, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.