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Linux Security Technologies

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There are different types of Linux Security Technologies. Discretionary Access Control, SELinux (Security Enhanced Linux), chroot jail, and iptables are just a few. This paper is only going to discuss the latter three. Discretionary Access Control is the more traditional, however; DAC is not as secure and will not be discussed here.1 The U.S National Security Agency (NSA) is the organization behind the creation of SELinux. The reason the NSA is involved in this project is because this organization is responsible for carrying out the research and advanced development of technologies needed to enable NSA to provide the solutions, products, and services to achieve Information Assurance for information infrastructures critical to U.S. National Security interests. The NSA implemented a Mandatory Access control within the Linux Kernel. This MAC is named Flask.2 There are three main policies that SELinux uses to apply MAC. There is the Targeted, where the MAC controls will only be used for a specific process or processes, there is the Multilevel Security protection, and the Strict. The strict puts MAC controls to all processes. The targeted is not as secure as the strict, however; the targeted is easier to maintain. If one uses the strict, the administrator will have to customize the policy. Failure to do so could cause other users a significant problem in performing his or her assigned duties. 3 The main reason the MAC has been created is to help prevent security threats to a system. Threats from user errors, software flaws, and malicious users can be reduced by implementing MAC. MAC will only allow the user to do the processes permitted by the policies applied. 4

The next Linux Security Technology to be discussed in this paper is chroot. There was not a particular organization behind this security technology. This utility was introduced in Version 7 of UNIX in 1979. 5 The chroot utility was designed to allow a user to run a particular process with a root directory that is not /. The root directory is always at the top of the hierarchy of paths and does not have a parent. Creating a root directory called chroot jail, may help in preventing a program from outside of the path from gaining access and causing harm to the system. 6 The biggest threat of this technology would be from a privileged user. Therefore, if an employee is leaving an organization the users rights should be stripped prior to this in order to prevent a malicious attack from an unhappy individual.7 Last of the three security technologies that will be discussed in this paper is iptables. This function actually uses two components, net filter and iptables. Netfilter contains the rules that the Linux kernel uses to control network packet filtering.8 The origin of Netfilter is Paul Russell. He was later joined by other individuals and they formed the organization, Netfilter.org, that maintains net filter/iptables.9 Iptables was designed to replace the earlier ipchains. Iptables provides a more flexible filter for networking. The chains are put into three different tables. There is the Filter table, NAT table, and the Mangle table. Nat (Network Address Translation Table is used to translate the destination source of the receiver of the packet. There are three different targets within the NAT tables. There is DNAT (destination NAT), which will change the destination of the in bound packet. Then there is the SNAT (source NAT), which will change the IP address of the outbound packet so the it will appear to be static

and not dynamic. The last of the three is the MASQUERADE. This will make sure the outbound IP address is compatible with a dynamic server. Filter tables are designed to either drop or accept packets based on their content and if there is a match or not to the established filter. Mangle alters the type of service. 10 This paper has provided information on three main Linux Security Technologies. First was the SELinux, which is used to design policies and controls on what a user is or not allowed to do. Second was the chroot, which helps prevent programs from causing harm by altering the root directory. And last technology discussed was the Netfilter/iptables, which is a way to control network packet sending and receiving. There is probably no one way to completely secure a system, but combing technologies as those discussed here can help improve the security of the system.

Notes

1. Mark G. Sobell, A Practical Guide to Fedora and Red Hat Enterprise Linux Ann Arbor, Michigan: Edward Brothers, 2010, 414-415.
2. National Security Agency, Security - Enhanced Linux, 15 January 2009. (9 April 12).
3. Sobell, A Practical Guide to Fedora and Red Hat Enterprise Linux, 414.
4. Sobell, A Practical Guide to Fedora and Red Hat Enterprise Linux, 414.
5. Wikipedia, chroot, June 2011 9 April 2012.
6. Sobell, A Practical Guide to Fedora and Red Hat Enterprise Linux, 448-449.
7. Wikipedia, chroot, June 2011
8. Sobell, A Practical Guide to Fedora and Red Hat Enterprise Linux, 820.
9. Netfilter.org, The Netfilter.org Project 1999-2010. 9 April 2012
10. Sobell, A Practical Guide to Fedora and Red Hat Enterprise Linux, 820.

Bibliography

Mark G. Sobell, A Practical Guide to Fedora and Red Hat Enterprise Linux Ann Arbor, Michigan: Edward Brothers, 2010.
National Security Agency, Security - Enhanced Linux, 15 January 2009. 9 April 2012.
Wikipedia, chroot, June 2011 9 April 2012.
Netfilter.org, The Netfilter.org Project 1999-2010. 9 April 2012

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