CHAPTER        3


In this chapter, we look at access control mechanisms used to protect larger-scale resources like files and folders. The chapter focuses on these topics:

•  Overview of file system technology

•  Structure of executable files and viruses

•  Goals and basic policies for file protection and sharing

•  File security controls based on “permission flags”

3.1 The File System

Data sharing poses a problem: If people can look at some information on a computer, how do we prevent them from seeing all the information? This is the same problem as RAM protection in Chapter 2. If any user can modify any information inside the computer, we can’t prevent users from reaching any of its contents.

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