Jonathan Walpole

Buffer overflows: attacks and defenses for the vulnerability of the decade

Buffer overflows have been the most common form of security vulnerability for the last ten years. More over, buffer overflow vulnerabilities dominate the area of remote network penetration vulnerabilities, where an anonymous Internet user seeks to gain partial or total control of a host. If buffer overflow vulnerabilities could be effectively eliminated, a very large portion of the most serious security threats would also be eliminated. In this paper, we survey the various types of buffer overflow vulnerabilities and attacks, and survey the various defensive measures that mitigate buffer overflow vulnerabilities, including our own StackGuard method. We then consider which combinations of techniques can eliminate the problem of buffer overflow vulnerabilities, while preserving the functionality and performance of existing systems.

Optimistic incremental specialization: streamlining a commercial operating system

Conventional operating system code is written to deal with all possible system states, and performs considerable interpretati on to determine the current system state before taking action. A consequence of this approach is that kernel calls which perform little ac tual work take a long time to execute. To address this problem, we use specialized operating system code that reduces interpretation for common cases, but still behaves correctly in the fully general c ase. We describe how specialized operating system code can be generated and bound incrementallyas the information on which it depends becomes available. We extend our specialization techniques to include the notion of optimistic incremental specialization : a technique for generating specialized kernel code optimistically for sys tem states that are likely to occur, but not certain. The ideas outlined in this paper allow the conventional kernel design tenet of “optimi zing for the common case” to be extended to the domain of adaptive operating systems. We also show that aggressive use of specialization can produce in-kernel implementations of operating system functionality with performance comparable to user-level implementations. We demonstrate that these ideas are applicable in real-world operating systems by describing a re-implementation of the HP-UX file system. Our specializedread system call reduces the cost of a single byte read by a factor of 3, and an 8 KB read by 26%, while preserving the semantics of the HP-UXread call. By relaxing the semantics of HP-UXread we were able to cut the cost of a single byte read system call by more than an order of magnitude.

Research challenges in environmental observation and forecasting systems

We describe Environmental Observation and Forecasting Systems (EOFS), a new class of large-scale distributed system designed to monitor, model, and forecast wide-area physical processes such as river systems. EOFS have strong social relevance in areas such as education, transportation, agriculture, natural resource planning and disaster response. In addition, they represent an opportunity for scientists to study large physical systems to an extent that was not previously possible. Building the next generation of EOFS pose a number of difficult challenges in all aspects of wireless networking, including media protocols for long distance vertical communication through water, flooding algorithms in ad-hoc network topologies, support for rate- and time-sensitive applications, and location-dependent mobile computing.

A Distributed Real-Time MPEG Video Audio Player

This paper presents the design, implementation and experimental analysis of a distributed, real-time MPEG video and audio player. The player is designed for use across the Internet, a shared environment with variable traffic and with great diversity in network bandwidth and host processing speed. We use a novel toolkit approach to build software feedback mechanisms for client/server synchronization, dynamic Quality-of-Service control, and system adaptiveness. Our experimental results show that the feedback mechanisms are effective, and that the player performs very well in the Internet environment.

Analysis of a reservation-based feedback scheduler

When executing soft real-time tasks in a shared processor, it is important to properly allocate the computational resources such that the quality of service requirements of each task are satisfied. In this paper we propose Adaptive Reservations, based on applying a feedback scheme to a reservation based scheduler After providing a precise mathematical model of the scheduler, we describe how this model can be used for synthesising the controller by applying results from control theory. Finally, we show the effectiveness of our method by simulation and by experiments with an MPEG player running on a modified Linux kernel.

Provisioning on-line games: a traffic analysis of a busy counter-strike server

This poster describes the results of a 500 million packet trace of a popular on-line, multiplayer, game server. The results show that the traffic behavior of this heavily loaded game server is highly predictable and can be attributed to the fact that current game designs target the saturation of the narrowest, last-mile link (i.e. 56k modems). Specifically, in order to maximize the interactivity of the game itself and to provide relatively uniform experiences between players playing over different network speeds, on-line games typically fix their usage requirements in such a way as to saturate the network link of their lowest speed players. While the traffic observed is highly predictable, the trace also indicates that these on-line games provide significant challenges to current network infrastructure. As a result of synchronous game logic requiring an extreme amount of interactivity, a close look at the trace reveals the presence of large, highly periodic, bursts of small packets. With such stringent demands on interactivity, routers must be designed with enough capacity to quickly route such bursts without delay. As current routers are designed for bulk data transfers with larger packets, a significant, concentrated deployment of on-line game servers will have the potential for overwhelming current networking equipment.

Player for adaptive MPEG video streaming over the Internet

This paper describes the design and implementation of a real-time, streaming, Internet video and audio player. The player has a number of advanced features including dynamic adaptation to changes in available bandwidth, latency and latency variation; a multi-dimensional media scaling capability driven by user-specified quality of service (QoS) requirements; and support for complex content comprising multiple synchronized video and audio streams. The player was developed as part of the QUASAR project at Oregon Graduate Institute, is freely available, and serves as a testbed for research in adaptive resource management and QoS control.

Flow and Congestion Control for Internet Media Streaming Applications

The emergence of streaming multimedia players provides users with low latency audio and video content over the Internet. Providing high-quality, best-effort, real-time multimedia content requires adaptive delivery schemes that fairly share the available network bandwidth with reliable data protocols such as TCP. This paper proposes a new flow and congestion control scheme, SCP (streaming control protocol), for real- time streaming of continuous multimedia data across the Internet. The design of SCP arose from several years of experience in building and using adaptive real-time streaming video players. SCP addresses two issues associated with real- time streaming. First, it uses a congestion control policy that allows it to share network bandwidth fairly with both TCP and other SCP streams. Second, it improves smoothness in streaming and ensures low, predictable latency. This distinguishes it from TCPs jittery congestion avoidance policy that is based on linear growth and one-half reduction of its congestion window. In this paper, we present a description of SCP, and an evaluation of it using Internet- based experiments.

Quality-adaptive media streaming by priority drop

This paper presents a general design strategy for streaming media applications in best effort computing and networking environments. Our target application is video on demand using personal computers and the Internet. In this scenario, where resource reservations and admission control mechanisms are not generally available, effective streaming must be able to adapt in a responsive and graceful manner. The design strategy we propose is based on a single simple idea, priority data dropping, or priority drop for short. We evaluate the efficacy of priority drop as an adaptation tool in the video and networking domains. Our technical contribution with respect to video is to show how to express adaptation policies and how to do priority-mapping, an automatic translation from adaptation policies to priority assignments on the basic units of video. For the networking domain, we present priority-progress streaming, a real-time best-effort streaming protocol. We have implemented and released a prototype video streaming system that incorporates priority-drop video, priority mapping, and priority-progress streaming. Our system demonstrates a simple encode once, stream anywhere model where a single video source can be streamed across a wide range of network bandwidths, on networks saturated with competing traffic, all the while maintaining real-time performance and gracefully adapting quality.

User-Level Implementations of Read-Copy Update

Read-copy update (RCU) is a synchronization technique that often replaces reader-writer locking because RCUs read-side primitives are both wait-free and an order of magnitude faster than uncontended locking. Although RCU updates are relatively heavy weight, the importance of read-side performance is increasing as computing systems become more responsive to changes in their environments. RCU is heavily used in several kernel-level environments. Unfortunately, kernel-level implementations use facilities that are often unavailable to user applications. The few prior user-level RCU implementations either provided inefficient read-side primitives or restricted the application architecture. This paper fills this gap by describing efficient and flexible RCU implementations based on primitives commonly available to user-level applications. Finally, this paper compares these RCU implementations with each other and with standard locking, which enables choosing the best mechanism for a given workload. This work opens the door to widespread user-application use of RCU.