Transcript Chapter 9, Security Modern Operating Systems by

Chapters 9 & 10,
Modern Operating Systems
by A. S. Tanenbaum
IA 705, Prof. Brown, Spring 2003
Group E
IA705, Spring 2003
J. Paloschavez, M. Troxler, J. Boggs,
J. Lagas Chapters 9 & 10 IA705
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Chapter 9, UNIX & Linux
Modern Operating Systems
by A. S. Tanenbaum
Group E
IA705, Spring 2003
J. Paloschavez, M. Troxler, J. Boggs,
J. Lagas Chapters 9 & 10 IA705
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Jose Paloschavez
J. Paloschavez, M. Troxler, J. Boggs,
J. Lagas Chapters 9 & 10 IA705
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The Security Environment
• Threats
• Intruders
• Accidental Data Loss
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Basics of Cryptography
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Secret-Key Cryptography
Public-Key Cryptography
One-Way Functions
Digital Signatures
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Authentication Using Passwords
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Authentication Using Passwords
Authentication Using a Physical Object
Authentication Using Biometrics
Countermeasures
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Matt Troxler
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Attacks from the Inside
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Trojan Horses
Login Spoofing
Logic Bombs
Trap Doors
Buffer Overflow
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Design Principles for Security
• Public Design - easier to service.
• Default = Deny Access - easier to trace
errors.
• Check access occasionally, not just a login
or file open procedure
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Design Principles Cont’d
• Minimal permissions for all users/processes.
• Ease of use - difficult interfaces usually
result in wide-open environments.
• Keep it simple - Tight and efficient code is
easy to review and lock down.
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External Attacks (Viruses)
How they function
• “Dropper” tool is used to deploy a virus
• Infected file is distributed (preferably
publicly)
• Users go get (or receive unknowingly) and
install the infected file
• Payload of the file runs, does whatever the
virus does
J. Paloschavez, M. Troxler, J. Boggs,
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Classifications of Viruses
• Companion virus - runs
in place of a legitimate
file
• Executables - virus code
imbeds itself in another
.exe (overwriting)
• Parasitic viruses overwriting, but the
original files still work
after infection.
• Cavity virus - virus
embeds itself in unused
portions of legit. files
• Memory Resident - Lives
in memory, little disk
activity
• Boot Sector - lives at the
first sector of the HDD
• Device Driver - gets
loaded as a legit. file in
kernel mode
• Macro - attached to a file
that appears innocent
• Source Code - requires
some knowledge of
programming
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How Viruses Spread
• Downloads
• Email
• Storage Space (fixed or removable disks,
memory, etc.)
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Antivirus and Anti-Antivirus…
and so on…
• Date hiding – Date
disguising – Parent
folder…
• Size hiding –
Compression
• Bitwise hiding –
Look for decryption
routine/key
Polymorphic
– Look for
morphing
routine code
Checksums
– Delete or
overwrite –
Encrypt
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Securing Mobile Code
• Sandboxing
• Interpretation
• Code
• Java Security
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Protection Mechanisms
• Protection Domains
• Access Control Lists
• Capabilities
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Trusted Systems and Multilevel
Security
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Trusted Computing Base
Formal Models
Bell-La Padula Model
Biba Model
Orange Book
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Covert Channels
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Chapter 10, UNIX & Linux
Modern Operating Systems
by A. S. Tanenbaum
Group E
IA705, Spring 2003
J. Paloschavez, M. Troxler, J. Boggs,
J. Lagas Chapters 9 & 10 IA705
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Jim Boggs
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History
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UNICS
PDP-11 UNIX & Portable UNIX
Berkeley UNIX
Standard UNIX & POSIX
MINIX
Linux
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Overview of UNIX
UNIX Goals & Interfaces
• Goals
– Handle Multiple Processes & Users
– Design Principles
• Interfaces
User Interface
Library Interface
System Call Interface
Users
Utility Programs
Standard Library
UNIX OS
Hardware
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User Mode
Kernel Mode
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Overview of UNIX
UNIX Shell & Utility Programs
• Shell
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Ordinary program providing command line interface
Standard input/output
Flexibility (wild cards, standard I/O,flags, pipes)
Shell Scripts
• Utility Programs
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File & Directory Commands
Filters
Development Tools & Text Processing
System Administration
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Overview of UNIX
Kernel Structure
• Simplified Kernel Drawing Here
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Processes in UNIX
Concepts and Process Management
• Active Entities are Processes
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Foreground & Background
Parent & Child
ID for Each
Single & Multiple Threads
• Process Management System Calls
– Means for Processes to Communicate
– Based on POSIX
– Examples
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Processes in UNIX
Implementation
• Process Table
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Scheduling Parameters
Memory Image
Signals
Miscellaneous
• Use Structure
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Machine Registers
System Call State
File Descriptor
Accounting
Kernel Stack
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Processes in UNIX
Threads
• UNIX
– Supported in Kernel, but Process-oriented
– Difficult Thought Process in Using Multiple Threads
• Fork & other Examples
• Linux
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Kernel-oriented
Clone
Detailed Sharing
Non-portability
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Processes in UNIX
Scheduling
• UNIX
– Designed for Response to Interactive Processes
– Process-oriented Queue Management
– Get Processes Rapidly out of the Kernel
• Linux
– Thread-oriented
– Classes of Linux Threads
• Real-time FIFO
• Real-time Round Robin
• Timesharing
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Processes in UNIX
Booting UNIX
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Get Kernel Running
Set Message Buffer
Allocate Kernel Data Structure
System Configuration (drivers)
– Static Links
– Dynamic Loads
• Begin Process 0
• Init
• Login
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Memory Management in UNIX
Concepts
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Text Segment
Data Segment
Stack Segment
Space Saving Techniques
– Shared Text Segments
– Memory-mapped Files
• No POSIX System Calls
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Memory Management in UNIX
Implementation in UNIX
• Swapping
– Early Concept
– Moving Process from Memory to Disk
– Moving Process from Disk to Memory
• Paging
– Entire Process Need Not be in Memory
– Kernel and Paging Daemon
– Replacement Algorithm
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Memory Management in UNIX
Implementation in Linux
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Default Allocation to each Process
Copy-on-Write
Three-level Paging
Kernel is Never Paged Out
Buddy Algorithm
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John Lagas
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I/O in UNIX
Concepts
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UNIX File System
Concepts
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Security in UNIX
Concepts
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