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Preventing Theft of Quality of
Service on Open Platforms
Kwang-Hyun Baek and Sean W. Smith
Department of Computer Science
Dartmouth College
[email protected]
This Talk
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Goal: Prevent insider’s theft of QoS while still permitting
the user to be root
Motivation: Dartmouth’s plan for traffic convergence
Summary
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Overview of threat model and Diffserv
Our solution
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Make end nodes trustworthy
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Trusted hardware and high assurance OS
Network authentication
Distribute Diffserv classifier and marker to end nodes
Security and performance discussions
Future work
Threat Model
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End node user with root account and physical
access
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Authenticated and authorized
Can install/modify hardware
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Can modify network driver, firmware, ROM
Can install/modify software, including kernel
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Can modify outgoing packets
Can modify a program’s packet generation
Can use arbitrary port for applications
Can spoof MAC address and IP address
Background: Diffserv
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Differentiated Services
At the Ingress/Egress nodes
 Classify packets via packet inspection
 Meter the temporal state of the packet (i.e., rate)
 Mark the packets’ Diffserv Code Point (DSCP) according to its
class
 Shape the packets (drop or delay)
At other nodes, Per-Hop Behavior (PHB) is applied based on
DSCP
 Assured Forwarding
 Expedited Forwarding
Problem
 End nodes are not trusted
 Network can gain only limited knowledge
Misbehaving Application
Ingress Network Node
Class Platinum
(Video streaming)
layer-3: UDP
application: RTP
ip set DSCP 46
End Node
Hacked
File Sharing app
Video Streaming
Class Best Effort
ip set DSCP 0
Misbehaving End Node
Ingress Network Node
End Node
Class Platinum
(Priority Client)
source MAC
00:04:00:00:00:00
MAC: 00:00:00:00:00:00
Spoofed MAC:
00:04:00:00:00:00
ip set DSCP 46
File Sharing
Malware
Class Best Effort
ip set DSCP 0
Our Solution
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Apply trusted computing to QoS
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Move Diffserv classifier and marker to each end node
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Use high assurance OS to create a configuration that
classifies and marks the packets according to the network’s
rule
Use trusted hardware to bind the configuration to
authentication secret
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Network’s QoS rule: hash of program binary and DSCP
If classifying and marking is modified, access to the
authentication secret is denied
Accessing the network  classifying and marking
according to the network’s QoS rule
Building Block: Trusted Platform
Module (TPM)
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Designed by Trusted Computing Group (TCG)
Measures the hardware and software configuration of the host
 Platform Configuration Registers
Attests the host’s configuration to a remote party
Stores RSA keys
Binds the stored RSA keys to a configuration
Problem
 Root can spy on memory used by the TPM
 Bound keys need to be changed too often if the configuration
includes programs that need frequent updates
 Root can change code after the TPM has measured it
 Need for high assurance OS with restricted access control and
integrity protection
Building Block: High Assurance OS
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SELinux Linux Security Module (NSA)
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Role-based mandatory access control
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Compartmentalization blocks memory spying
Robust access control over devices, memories, files, socket
structures
Enforcer LSM (Marchesini, et al)
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Makes TPM-bound keys more usable
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Long term (hardware, OS, Admin’s public key, SELinux policy)
protected by TPM-bound key
Medium term (programs, kernel modules, libraries, linkers) protected
by the LSM and Security Admin—a third party who issues signed
database of trustworthy applications
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Integrity Protection (modification results in TPM lock or kernel panic)
Short term (data, configuration) protected by encrypted file system
Distributed Classifier and Marker
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QoS Admin
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Issues signed database of program binary’s hash
and the DSCP it should receive
Modified LSM
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The kernel keeps track of which opened socket
belongs to which program (Socket monitor)
The kernel marks each packet’s DSCP at the
kernel’s IP layer using Netfilter (standard Linux
firewall) hooks, according to the QoS Admin’s
signed database (DSCP marker)
Socket Monitor
App X calls
socket syscall
Is App X in Security
Admin's Policy?
YES
YES
Is App X found in
QoS Admin's Policy?
Record
socket, h(X), DSCP
NO
Log and return
(will be dropped)
NO
Record
socket, h(X), default DSCP
DSCP Marker
Outgoing packet enters
IP Layer
YES
Is the packet
coming from a recorded
socket?
Modify the packet's DSCP
to the recorded value
NO
Drop
Adding Client Authentication
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Uses TPM-bound key (EAP-TLS)
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EAP-TLS authentication requires the knowledge of the private
key
During certification, the CA checks the long term
configuration of the host
To access the TPM-bound private key to authenticate
itself to the network, an end node must do the following:
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Be in the long term configuration to which the key is bound to
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Run Enforcer LSM, SELinux, and our socket monitor and DSCP
marker
Run valid Security Admin and QoS Admin’s databases (their
signature is validated)
SELinux is using a known, trustworthy SELinux policy
Have not modified important medium term configuration
Stopping Misbehaving Application
End Node
Class Platinum
Linphone
Gnomemeeting
ip set DSCP 46
Class Best Effort
ip set DSCP 0
Class Blacklist
Drop
Hacked
File Sharing
Linphone (VoIP)
Stopping Misbehaving End Node
End Node
Class Platinum
Linphone
Gnomemeeting
ip set DSCP 46
Class Best Effort
ip set DSCP 0
Class Blacklist
Drop
Hacked Wireless Driver
and its firmware
to gain better QoS
Configuration mismatch
results in TPM lock or
kernel panic
Cannot access
the authentication
private key!
Performance evaluation
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IBM T40, Pentium M 1.3 GHz, 256 MB
Overhead caused by socket monitor
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Overhead caused by DSCP marking
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4.86 ms average delay for linphone
0.0087 ms average delay for linphone
ITU recommends maximum delay of 150 ms
for voice system
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The Overhead is easily absorbed
Security Considerations
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Forked children inherit sockets
 QoS Admin’s job to control the QoS level of the programs that
fork and exec other programs
 Another option: least privilege principle for shared socket
SELinux should prohibit low-privileged programs from piping
packets to high-privileged programs
Hardware spying on TPM
 No Plug-and-Play, USB/Firewire devices should be disabled at
the kernel level
EAP-TLS results in session keys for encryption and integrity
protection
 Compartmentalize to block spying on session keys
 No man-in-the-middle attack between ingress node and end node
Future Work
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Attestable, cleaner, easy-to-understand policies for
SELinux
Migratable QoS and Security Admin database
Database version check and automatic update
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Boot-time generation of attribute certificate containing the
policy version, signed by the TPM-bound key
Quarantined database updating using VLAN
Bigger scale testing
Performance evaluation depending on system loads
Code will be available at
http://enforcer.sourceforge.net
 Or email me until then for the kernel patch
Thanks
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We thank our sponsors—Mellon Foundation,
Cisco, Intel, and the Office for Domestic
Preparedness (U.S. Dept of Homeland
Security)
Questions?