Protection
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This document discusses various concepts related to protection in operating systems. It covers the goals of protection which include preventing unauthorized access and enforcing access policies. The principle of least privilege is introduced which dictates that users and programs be given only necessary privileges. Access control and its basic terminology like objects, access rights and access control policies are defined. Implementation techniques for access control like access matrix, access control lists, capability lists and language-based approaches are described at a high level. The document provides an overview of key protection concepts in operating systems.
Protection
- 1. PROTECTION Submitted to: Submitted by: Miss. Namita Jain Krati Katyal MCA 3rd Sem
- 2. Topic Covered • INTRODUCTION • GOALS OF PROTECTION • PRINCIPLE OF PROTECTION • ACCESS CONTROL • DOMAIN • ACCESS MATRIX • IMPLEMENTATION OF ACCESS MATRIX • CAPABILITY BASED SYSTEM • LANGUAGED BASED SYSTEM
- 3. Introduction • Protection refers to a mechanism for controlling the access of programs, processes, or users to the resources defined by a computer system. • Protection ensures that the resources of the computer are used in a proper way. • It ensure that each object accessed correctly and only by those processes that are allowed to do so. • OS designer faces challenge of creating a protection scheme that cannot be by passed by any software that may be created in the future
- 4. Goals of Protection • We need to provide protection for several reasons. The most obvious is the need to prevent the bad, intentional violation of an access restriction by user. • An unprotected resource cannot defend against misuse by an unauthorized user. A protection-oriented system provides means to distinguish between authorized and unauthorized usage.
- 5. • The role of protection in a computer system is to provide a mechanism for the implementation of the policies governing resource use. • These policies can be established in a variety of ways. Some are fixed in the design of the system, while others are formulated by the management of a system. Still others are defined by the individual users to protect their own files and programs. • A protection system must have the flexibility to enforce a variety of policies.
- 6. Principle of Protection • The time-tested guiding principle for protection is the Principle of least privilege. It dictates that programs, users, and even systems be given just enough privileges to perform their tasks. • The principle of least privilege can help produce a more secure computing environment.
- 7. • Access control is concerned with determining the allowed activities of valid users, mediating every attempt by a user to access a resource in the system. • Basic Terminology are : Access Control Object: An entity that contains or receives information. - Access to an object potentially implies access to the information it contains. example. File, programs, printer, disk, etc. Access rights: The permisiion granted to a user to perform an operation example. read, write, execute etc
- 8. Access Conrol policy object source (e.g. users, processes) request guard resource (e.g. files, printers) Access request subject
- 9. • Domain = collection of objects and a set of access rights for each of the objects • A process operates within a Protection Domain that specifies the resources that the process may access. • Each domain defines a set of objects and the types of operations that may be invoked on each object. • The ability to execute an operation on an object is an access right • System will consists of such multiple domains each having certain predefined access right on different object Domain
- 10. • During execution of the process it can change the domain this is called domain switching • A domain can be realized in a variety of ways: • Each user may be a domain. In this case, the set of objects that can be accessed depends on the identity of the user. • Each process may be a domain. In this case, the set of objects that can be accessed depends on the identity of the process.
- 11. Example of Unix: In the UNIX operating system, a domain is associated with the user In Unix operating system user ID’s use for identify the domain.
- 12. • View protection as a matrix (access matrix) • Rows represent domains • Columns represent objects • Each entry in the matrix consists of a set of access rights. • The entry access(i,j) defines the set of operations that a process executing in Domaini can invoke on Objectj Access Control Matrix
- 13. • If a process in Domain Di tries to do “operation” on object Oj, then “operation” must be in the access matrix. Fig : Access contol matrix object domain F1 F2 F3 PRINTE R D1 read execut e D2 read write read D3 execute read D4 read read write
- 14. Access matrix design separates mechanism from policy Mechanism Operating system provides access-matrix + rules It ensures that the matrix is only manipulated by authorized agents and that rules are strictly enforced Policy User dictates policy Who can access what object and in what mode Use of Access Matrix
- 15. Access Matrix of Figure A With Domains as Objects Figure B
- 16. Access Matrix with Copy Rights
- 17. Access Matrix With Owner Rights
- 18. Implementation of Access Control Matrix Each column = Access-control list for one object Defines who can perform what operation. Domain 1 = Read, Write Domain 2 = Read Domain 3 = Read Each Row = Capability List (like a key) Fore each domain, what operations allowed on what objects. Object 1 – Read Object 4 – Read, Write, Execute Object 5 – Read, Write, Delete, Copy
- 19. Global Table The simplest implementation of the access matrix Table consists of set of ordered triples<Domain, object, right set> Whenever an operation M is executed on object(Oj) with domain(Di) then a global table is searched for triple<Di, Oj, Rk> If found, operation is allowed to continue otherwise it deny access It has several disadvantage Usually large thus cannot be kept in main memory. Additional I/O is needed It must have separate entry in domain
- 20. Access Control Lists (ACLs) • Focus on the object – ACLs ≡ columns of the access control matrix Oj <Di , Rk> • ACL define all domain with non empty set of access rights for that object • Access rights are often defined for groups of users – because individual subjects may create a huge list • ACL is stored in the directory entry of the file − BFD(Basic file directory) is the right place to maintain the ACL
- 21. Capability List • Focus on the subject Capabilities list ≡ rows of the access control matrix • Capability is pointer to the object, contain address of the object • Each domain has its capability list which contain list of capability together with operation allowed • Capability list is itself a protected object Maintained by operating system Accessed by user only indirectly
- 22. Address space split into two parts - One parts is accessible to the program and other part contains capabilities which is accessible only by OS Contd…..
- 23. Locks and Keys • The lock key scheme is a compromise between access list and capability list. • Each object has a list of unique bit patterns called Locks • Each domain has a list of unique bit pattern called Keys • A process executing in a domain can access an object only if that domain has a key that match one of the locks of the object -
- 24. Capability Based System Hydra Fixed set of access rights known to and interpreted by the system Analysis of user-defined rights performed only by user's program; system provides access protection for use of these rights Cambridge CAP System Data capability - provides standard read, write, execute of individual storage segments associated with object Software capability -interpretation left to the subsystem, through its protected procedures
- 25. Language Based Protection Specification of protection in a programming language allows the high-level description of policies for the allocation and use of resources Language implementation can provide software for protection enforcement when automatic hardware-supported checking is unavailable
- 26. Reference • www.google.com • www.wikipidea.com • Silberschatz, A and Galvin, P.B., Operating System Concepts, Addison Wesely, 2004
- 27. MLSU UNIVERSITY