Network Security Tools

Chapter 7. Fun with Linux Kernel Modules

The kernel is the heart of an operating system. It is responsible for such core functionality as memory management, process scheduling, TCP/IP networking, and so on. Linux Kernel Modules (LKMs) allow you to extend Linux kernel functionality on-the-fly. Because it is easy to insert and remove LKMs using command-line tools, malicious users prefer to install LKM-based rootkits and backdoors on a compromised system to maintain access to the host. This chapter will show you how to write your own LKMs and teach you how authors of malicious rootkits and backdoors leverage the power of LKMs to perform various types of tricks, such as process and file hiding as well as system call interception. This chapter assumes you are familiar with the C programming language.

Warning

Do not run the examples presented in this chapter on mission-critical or production hosts. A simple error in an LKM can cause a kernel to panic, which will crash the running kernel. If possible, use virtual machine software such as VMware (http://www.vmware.com/) to run the source code presented in this chapter.