Transcript Poornakumar Rasiraju`s presentation on Usable Mandatory Integrity

Usable Mandatory Integrity
Protection for Operating Systems
Authors: Ninghui Li, Ziqing Mao and Hong Chen
“IEEE Symposium on Security and Privacy(SP’07)”
By:Poornakumar Rasiraju
Introduction
• Host compromise is one of the most serious security
problems today.
• What is the problem with the compromised hosts?
Form Botnets which can be used to carry out the attacks
such as phishing, Spamming and Distributed denial of
service.
• Can we deal with these threats at the network level?
Partially, by using technologies such as Firewall and
Network Intrusion Detection System.
Introduction..
• Two reasons why hosts can be easily compromised?
Software is buggy.
Discretionary access control mechanisms are insufficient to
defend against network-based attacks.
• Are there any efforts to make computer systems secure?
Adding MAC to Operating Systems such as SELinux,
AppArmor, Systrace and LOMAC.
Introduction….
• Then what is the problem?
They are complex and difficult to configure.
For example, SELinux.
--29 different classes of objects
--hundreds of operations
--Thousands of policy rules
SELinux policy interface is daunting even for security experts.
Outline
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Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model
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Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Outline
•
•
•
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Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model
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•
•
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Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Six Design Principles for Usable Access
Control Systems
• Principle 1: Provide “good enough” security with a high level
of usability, rather than “better” security with a low level of
usability.
Aim at providing a system that is easy to configure which can greatly
increase the level of security by reducing the attack surfaces.
• Principle 2: Provide policy, not just mechanism.
The mechanism-not-policy approach is problematic for security.
• Principle 3: Have a well-defined security objective.
In order to make a meaningful tradeoff between security and usability, we
must identify the security objective and it is the first step in designing a
policy.
Six Design Principles for Usable Access
Control Systems ..
• Principle 4: Carefully design ways to support exceptions in the
policy model.
One must carefully design the policy model and the exception mechanisms
so that the number of exceptions are small.
• Principle 5: Rather than trying to achieve “Strict least
privilege”, aim for “good –enough least privilege”.
Trying to achieve Strict least privilege results in large number of policy
rules.
Minimize the policy rules.
• Principle 6: Use familiar abstractions in the policy
specification interface.
The policy specification interface should use concepts and abstractions that
administrators are familiar with.
Outline
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Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model
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•
•
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•
Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Security Goal of the UMIP Model
• Aim: To protect the system integrity against network
based attacks.
• Assumptions:
 Network server and client programs contain bugs
 Users may make careless mistakes
Example: Downloading and running of malicious programs from the
internet.
 Attacker doesn’t have physical access to the host to be protected.
• What does the proposed Model achieve?
Attacker can only get limited privileges and cannot
compromise system integrity.
Outline
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•
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Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model
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•
•
•
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Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Usability Goals of the UMIP Model
• Usability Goals for UMIP are twofold:
 Configuring a UMIP system should not be difficult.
 Existing applications can still be used under UMIP.
• Administrator can configure the system in an easier
manner depending upon needs.
• UMIP can be implemented by using the Linux security
Module Framework.
Outline
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Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model
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Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Overview
• uid, gid is too coarse-granulated, a natural extension is to
treat a triple of uid, gid and the current program that is
running in the process as a principal.
• In order to determine what the current process should be
allowed to do, one has to consider the parent process and
so on… We call this the request channel.
• How to capture the information in a request channel is a
key challenge.
• UMIP Model:Each process has one bit that denotes its integrity level.
When a process is created, it inherits the integrity level of
the parent process.
 If the request channel is likely to be exploited by an attacker,
then the process has low integrity.
 If the request channel is legitimately used for system
administration, then the process has high integrity.
The UMIP Model is extended with exceptions to support
existing software.
Fig: The Summary of the UMIP Model
Outline
•
•
•
•
Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model






•
•
•
•
Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Dealing with communications
• The process integrity level drops, when it receives remote
network traffic.
• In the UMIP Model, the process running the program
(RAP), maintains its integrity level when receiving
network traffic.
• RAP is introduced to trade off security in favor of
usability.
• The UMIP Model leaves the decision of whether to allow
remote administration or not to the system administrators.
Outline
•
•
•
•
Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model






•
•
•
•
Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Restricting Low integrity process
• Security critical operations are classified into two
categories:- File operations and non-file administrative
operations.
• In modern Linux, the operations are controlled by
capabilities.
• The default UMIP rule grants only two capabilities
CAP_SETGID and CAP_SETUID to low-integrity
process.
Restricting Low integrity process..
• Low integrity process running as root cannot set its uid to
a new normal user.
• To identify which files should be considered sensitive is a
challenging task.
 Utilizes the valuable information in existing Discretionary
Access Control (DAC) mechanisms for MAC.
 A low integrity process is forbidden from changing the DAC permission
of any (read- or write-) protected file.
• Exception policies
 The binary “/usr/sbin/vsftpd” is allowed to use the capabilities
CAP_NET_BIND_SERVICE, CAP_SYS_SETUID, CAP_SYS_SETGID
and CAP_SYS_CHROOT, to read the file /etc/shadow, to read all files
under the directory /etc/vsftpd, and to read or write the file
/var/log/xferlog.
Outline
•
•
•
•
Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model






•
•
•
•
Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Contamination through files
• Process integrity level drops after reading and executing
files that are not write-protected.
 Even if a file is write-protected, it may still be written by lowintegrity process, due to the exception policies.
• Sticky bit is used to track contamination for files.
• A low-integrity process is forbidden from changing the
sticky bit of a file.
• The sticky bit can be reset by a special utility program
provided by the protection system.
Outline
•
•
•
•
Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model






•
•
•
•
Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Files owned by Non-System Accounts
• UMIP allows exceptions to be specified for specific users.
• Global exceptions can be applied to all processes with
that users user id as specified in the account’s exception
policy.
• A low-integrity process is disallowed from using setuid
to change its user id to another user account.
Outline
•
•
•
•
Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model






•
•
•
•
Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Design principles in UMIP
• Principle 1:Aimed at providing good enough security
with high level of usability.
• Principle 2&3:Used an existing mechanism and focused
on designing a policy to achieve the security objective.
• Principle 4:Designed Exception Mechanisms.
• Principle 5:Two design choices were made to increase the
simplicity of the model.
 No limitation is placed on high-integrity process.
 Non-sensitive files are not protected.
• Principle 6:Uses files and capabilities
specifications.
in policy
Outline
•
•
•
•
Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model






•
•
•
•
Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Novel features of UMIP
• UMIP has the following novel features:
 Supports a number of ways to specify some programs as
partially trusted.
 A file has two integrity level values.
 Integrity protection is compartmentalized by users.
 Allows low-integrity files to be upgraded to high-integrity.
 In addition to integrity protection, it offers some confidentiality
protection.
 Uses DAC information to determine integrity and confidentiality
labels for objects.
Outline
•
•
•
•
Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model






•
•
•
•
Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Implementation
• When a process issues a request, it should be authorized
by both Linux DAC system and UMIP .
• Exceptions must be specified in a policy file.
• The policy file includes a list of entries. Each entry
contains four fields:
1)
2)
3)
4)
A path that points to the program
The type of a program
A list of exceptions
A list of executing relationships
Implementation..
Syntax
Meaning
(f, read)
f is a regular file or a directory
Allowed to read f
(f, full)
f is a regular file or a directory
Allowed to do anything to f
(f, read, R)
d is a directory
Allowed to read any file in d
recursively
(f, full, R)
d is a directory
Allowed to do anything to any
file in d recursively
Figure: The four forms of file exceptions in UMIP.
Fig: Sample Policy
Outline
•
•
•
•
Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model






•
•
•
•
Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Evaluation
• Evaluation of the UMIP Model:
 Usability
 Transparency
 Flexibility
 Ease of configuration
 Security
 Installing a rootkit
 Kernel-mode rootkit
 User-mode rootkit
 Stealing the shadow file
 Altering web files.
 Performance
Benchmark
Base
Enforcing
Overhead(%)
SELinux(%)
Dhrystone
335.8
334.2
0.5
Double-precision
211.9
211.6
0.1
Execl Throughput
616.6
608.3
1
5
File Copy 1K
474.0
454.2
4
5
File Copy 256B
364.0
344.1
5
10
File Copy 4K
507.5
490.4
3
2
Pipe Throughput
272.6
269.6
1
16
Process Creation
816.9
801.2
2
2
Shell Scripts
648.3
631.2
0.7
4
System Call
217.9
217.4
0.2
Overall
446.6
435.0
3
Fig: The performance results of Unixbench 4.1 measurements
Outline
•
•
•
•
Six design principles for Usable Access Control Systems.
Security Goal of the UMIP Model
Usability goals of the UMIP Model
UMIP Model






•
•
•
•
Overview
Dealing with Communications
Restricting Low integrity process
Contamination through files
Files owned by Non-System Accounts
Design principles in UMIP
Novel features of UMIP
Implementation
Evaluation
Conclusion
Conclusion
• The UMIP Model defends against network-based attacks
and preserves the system integrity. It supports existing
applications and system administration practices, and has
a simple policy configuration interface.
References
• K.J.Biba . Integrity considerations for secure computer systems. Technical
Report MTR-3153, MITRE.
• U. Shankar, T. Jaeger, and R. Sailer. Toward automated information-flow
integrity verification for security-critical applications. In Proceedings of
the2006 ISOC Networked and Distributed Systems Security Symposium,
February 2006.
• T. Fraser. LOMAC: Low water-mark integrity protection for COTS
environments. In 2000 IEEE Symposium on Security and Privacy, May
2000.
• P. Loscocco and S. Smalley. Integrating flexible support for security
policies into the Linux operating system. In Proceedings of the FREENIX
track: USENIX Annual Technical Conference.