Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Linux kernel is the central component of Linux operating systems. It is responsible for managing the system's resources, the communication between hardware and software and security. Kernel play a critical role in supporting security at higher levels. Unfortunately, stock kernel is not secured out of box. There are some important Linux kernel patches to secure your box. They differ significantly in how they are administered and how they integrate into the system. They also allow for easy control of access between processes and objects, processes and other processes, and objects and other objects. The following pros and cons list is based upon my personal experience.
Security-Enhanced Linux (SELinux) is a Linux feature that provides a variety of security policies for Linux kernel. It is included with CentOS / RHEL / Fedora Linux, Debian / Ubuntu, Suse, Slackware and many other distributions.
AppArmor (Application Armor) is another security software for Linux which maintained and released by Novell under GPL. AppArmor was created as an alternative to SELinux. AppArmor works with file paths.
grsecurity is a set of patches for the Linux kernel with an emphasis on enhancing security. It utilizes a multi-layered detection, prevention, and containment model. It is licensed under the GPL.