Protection

Protection refers to controlling the access of programs, processes or users to the resources defined by a computer system.

Principle of least privilege: dictates that programs, users, and even systems be given just enough privileges to perform their tasks.

Need to know principle: a process should be able to access only those resources that it currently requires to complete its task.

A process operates within a protection domain, which specifies which resoures the process may access. The ability to execute an operation on an object is an access right.

In UNIX a domain is associated with the user. An owner identification and domain bit (setuid bit) are associated with each file. When the setuid bit is on and a user executes the file the user id is set to that of the owner of the file. When the bit is off the user id does not change.

Summary

Computer contain many objects (memory, CPU, I/O devices, files, programs, semaphores) and they need to be protected from abuse. An access right is permission to perform an operation on an object. A domain is a set of access rights. Processes execute in domains and may use any of the access rights in the domain. A process may be bound to a specific domain or allowed to switch from one domain to another.