Introducing Linux Security

              In this chapter, I explain why you need to worry about security and give you a high-level view of how to get a handle on security. I explain the idea of an overall security framework and explain the two key aspects of security — host security and network security. I end this chapter by introducing you to the terminology used in discussing computer security.

 

Why Worry about Security?

     In today’s networked world, you have to worry about your Linux system’s
     security. For a standalone system, or a system used in an isolated local area
     network (LAN), you have to focus on protecting the system from the users
     and the users from one another. In other words, you don’t want a user to
     modify or delete system files, whether intentionally or unintentionally. Also,
     you don’t want a user destroying another user’s files.
     If your Linux system is connected to the Internet, you have to secure the
     system from unwanted accesses over the Internet. These intruders — or
     crackers, as they are commonly known — typically impersonate a user, steal
     or destroy information, and even deny you access to your own system
     (known as a Denial of Service or DoS attack).
     By its very nature, an Internet connection makes your system accessible to
     any other system on the Internet. After all, the Internet connects a huge
     number of networks across the globe. In fact, the client/server architecture
     of Internet services, such as HTTP (Web) and FTP, rely on the wide-open
        network access the Internet provides. Unfortunately, the easy accessibility
        to Internet services running on your system also means that anyone on the
        Net can easily access your system.
        If you operate an Internet host that provides information to others, you cer-
        tainly want everyone to access your system’s Internet services, such as FTP
        and Web servers. However, these servers often have vulnerabilities that
        crackers may exploit in order to cause harm to your system. You need to
        know about the potential security risks of Internet services — and the pre-
        cautions you can take to minimize the risk of someone exploiting the weak-
        nesses of your FTP or Web server.
        You also want to protect your company’s internal network from outsiders,
        even though your goal is to provide information to the outside world through
        a Web or FTP server. You can protect your internal network by setting up an
        Internet firewall — a controlled access point to the internal network — and
        placing the Web and FTP servers on a host outside the firewall.