Operating System Security - Operating System - Lecture Slides, Slides of Computer Science

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Operating System Security

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Loscocco & Smalley (2001):

SE Linux

• Example operating system operations
  • Modify a file, read from a video camera, wait for a connection on a socket, create a new process
• Question: When should a process be allowed to perform certain operations?
• Discretionary Access Control (DAC)
  • Decisions to allow/disallow operations based on user identity & ownership
• Claim: this is insufficient when providing operating system security - Traditionally, with DAC, “every program executed by [a] user inherits all of the privileges associated with that user” (p. 1, ms.) Docsity.com

Policies vs. Mechanisms

• Different types of organizations may have different types of security needs
• Goals
  • Flexible support for security policies
  • Separate enforcement mechanisms-- mechanisms that enforce policy-- from policy itself
  • Individual organizations can create their own policies

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SE Linux

• Security server & policy “programming” language - Security server: New kernel component
• Mandatory Access Control (MAC) integrated into operations on 28 object classes, including - Processes - Files (and raw disks) - Sockets
• Security ID’s (SID’s) are bound to every object
• Permission checks are made between a source SID and a target SID - E.g., SID’s associated with a calling process and a file Docsity.com

Example: sendmail

• Similarly, other system programs also run

with limited privileges allow sendmail_t etc_aliases_t:file { read write };

allow sendmail_t etc_mail_t:dir

{ read search add_name remove_name };

allow sendmail_t etc_mail_t:file

{ create read write unlink };

See also: http://world.std.com/~franl/worm.html Docsity.com

More sendmail privileges

allow sendmail_t smtp_port_t:tcp_socket name_bind;

allow sendmail_t mail_spool_t:dir

{ read search add_name remove_name };

allow sendmail_t mail_spool_t:file

{ create read write unlink };

allow sendmail_t mqueue_spool_t:dir

{ read search add_name remove_name };

allow sendmail_t mqueue_spool_t:file

{ create read write unlink }; Docsity.com