Detecting corrupted pages in M replicated large files

A file in a distributed database system is replicated on M sites and may contain corrupted pages. Abdel-Ghaffar and El Abbadi gave a detection scheme assuming that the number of corrupted pages f < M l 2. We replace this assumption by a much weaker one, that, for each page, the majority of copies are correct. Our schemes are based on the structure of the Reed-Solomon code, as proposed by Abdel-Ghaffar and El Abbadi for M= 2. © 1997 IEEE.published_or_final_versio

Exterminator: Automatically Correcting Memory Errors with High Probability

Programs written in C and C++ are susceptible to memory errors, including buffer overflows and dangling pointers. These errors, which can lead to crashes, erroneous execution, and security vulnerabilities, are notoriously costly to repair. Tracking down their location in the source code is difficult, even when the full memory state of the program is available. Once the errors are finally found, fixing them remains challenging: even for critical security-sensitive bugs, the average time between initial reports and the issuance of a patch is nearly one month. We present Exterminator, a system that automatically corrects heap-based memory errors without programmer intervention. Exterminator exploits randomization to pinpoint errors with high precision. From this information, Exterminator derives runtime patches that fix these errors both in current and subsequent executions. In addition, Exterminator enables collaborative bug correction by merging patches generated by multiple users. We present analytical and empirical results that demonstrate Exterminator’s effectiveness at detecting and correcting both injected and real faults

Building Reliable Software for Persistent Memory

Persistent memory (PMEM) technologies preserve data across power cycles and provide performance comparable to DRAM. In emerging computer systems, PMEM will operate on the main memory bus, becoming byte-addressable and cache-coherent. One key feature enabled by persistent memory is to allow software directly accessing durable data using the CPU’s load/store instructions, even from the user-space.However, building reliable software for persistent memory faces new challenges from two aspects: crash consistency and fault tolerance. Maintaining crash consistency requires the ability to recover data integrity in the event of system crashes. Using load/store instructions to access durable data introduces a new programming paradigm, that is prone to new types of programming errors. Fault tolerance involves detecting and recovering from persistent memory errors, including memory media errors and scribbles from software bugs. With direct access, file systems and user-space applications have to explicitly manage these errors, instead of relying on convenient functions from lower I/O stacks.We identify unique challenges in improving reliability for PMEM-based software and propose solutions. The thesis first introduces NOVA-Fortis, a fault-tolerant PMEM file system incorporating replication, checksums, and parity for protecting the file system’s metadata and the user’s file data. NOVA-Fortis is both fast and resilient in the face of corruption due to media errors and software bugs.NOVA-Fortis only protects file data via the read() and write() system calls. When an application memory-maps a PMEM file, NOVA-Fortis has to disable file data protection because mmap() leaves the file system unaware of updates made to the file. For protecting memory-mapped PMEM data, we present Pangolin, a fault-tolerant persistent object library to protect an application’s objects from persistent memory errors.Writing programs to ensure crash consistency in PMEM remains challenging. Recovery bugs arise as a new type of programming error, preventing a post-crash PMEM file from recovering to a consistent state. Thus, we design two debugging tools for persistent memory programming: PmemConjurer and PmemSanitizer. PmemConjurer is a static analyzer using symbolic execution to find recovery bugs without running a compiled program. PmemSanitizer contains compiler instrumentation and run-time recovery bug analysis, compensating PmemConjurer with multi-threading support and store reordering tests

A Framework for Analyzing Advanced Malware and Software

Vulnerabilities in software, whether they be malicious or benign are a major concern in every sector. My research broadly focused on security testing of software, including malware. For the last few years, ransomware attacks have become increasingly prevalent with the growth of cryptocurrencies.The first part of my research presents a strategy to recover from ransomware attacks by backing up critical information in slack space. In this work, I designed RDS3, a novel ransomware defense strategy, in which we stealthily back up data in the spare space of a computing device, such that the data encrypted by ransomware can be restored. The key concept is that unused space can backup critical data, which is fully isolated from the system. In this way, no ransomware will be able to \u27\u27touch\u27\u27 the backup data regardless of what privilege it is able to obtain.Next, my research focused on understanding ransomware from both structural and behavioral perspectives to design CRDETECTOR, crypto-ransomware detector. Reverse engineering is performed on executables at different levels such as raw binaries, assembly codes, libraries, and function calls to better analysis and interpret the purpose of code segments. In this work, I applied data-mining techniques to correlate multi-level code components (derived from reverse engineering process) to find unique signatures to identify ransomware families.As part of security testing of software, I conducted research on InfiniBand (IB) which supports remote direct memory access without making two copies of data (one in user space and the other in kernel space) and thus provides very low latency and very high throughput. To this end, for many industries, IB has become a promising new inter-connect protocol over Ethernet technologies and ensuring the security of is critical. To do this, the first step is to have a thorough understanding of the vulnerabilities of its current implementations, which is unfortunately still missing in the literature. While my extensive penetration testing could not find any significant security loopholes, there are certain aspects in both the design and the implementations that need to be addressed

Techniques for building highly available distributed file systems

This paper analyzes recent research in the field of distributed file systems, with a particular emphasis on the problem of high availability. Several of the techniques involved in building such a system are discussed individually: naming, replication, multiple versions, caching, stashing, and logging. These techniques range from extensions of ideas used in centralized file systems, through new notions already in use, to radical ideas that have not yet been implemented. A number of working and proposed systems are described in conjunction with the analysis of each technique. The paper concludes that a low degree of replication, a liberal use of client and server caching, and optimistic behavior in the face of network partition are all necessary to ensure high availability