Design And Implement A Stackable File System Running On Linu ✓ Solved

Design and implement a stackable file system running on Linu

Design and implement a stackable file system running on Linux, which uses Amazon S3 as backend storage. The file system must meet the following requirements: once mounted, a bucket in S3 appears as a local directory; any updates (creation, deletion or modification of files and subdirectories) in the local directory are reflected in the corresponding S3 bucket and vice versa; and all files are encrypted transparently using RC4 so applications operate without explicit decryption. You may use and modify FUSE, s3fs, and OpenSSL. The report should describe project goals, system information and tools used, design diagrams, integration and results, implementation details highlighting source-code modifications, future improvements, and a summary of lessons learned.

Paper For Above Instructions

Introduction

This project implements a stackable Linux file system that mounts an Amazon S3 bucket as a local directory and synchronizes changes bidirectionally while applying transparent RC4 encryption for file contents. The goal is to enable standard POSIX applications to read and write files without managing encryption explicitly, while using S3 as persistent backend storage.

Project Goals

  • Expose an S3 bucket as a POSIX-like mount point on a Linux host (mount semantics and directory structure).
  • Ensure bidirectional synchronization: local filesystem operations reflect in S3 and S3 changes are visible locally.
  • Provide transparent RC4 encryption/decryption for all file contents so applications operate without explicit cryptographic calls.
  • Use and, where necessary, modify existing tools: FUSE for user-space file system framework, s3fs for S3 integration, and OpenSSL for cryptographic primitives.

System Information (Example)

Reference development environment used for design and testing:

  • CPU: Intel Core i7-6700K
  • Memory: 16 GB DDR4
  • OS: Ubuntu 20.04 LTS, Linux kernel 5.4
  • FUSE: libfuse 3.x [2]
  • s3fs: s3fs-fuse (latest stable release) [3]
  • OpenSSL: 1.1.1 or later for cipher primitives [4]

Tools and Packages

Primary components:

  • FUSE (Filesystem in Userspace) to implement a stackable user-space filesystem layer [2].
  • s3fs-fuse to manage S3 object mapping, metadata caching, and S3 API calls [3].
  • OpenSSL to provide RC4 stream cipher implementation and key management support [4].
  • AWS SDK/CLI for administrative tasks and verifying S3-side object state [1].
  • Auxiliary utilities: build tools (gcc/make), git, and testing frameworks (bash/python scripts).

Design

The design follows a layered (stackable) approach: a thin encryption layer sits above the s3fs-backed filesystem. FUSE provides the user-space entry points (lookup, read, write, create, unlink, readdir, getattr, etc.). s3fs maps filenames to S3 object keys and handles object upload/download. The encryption layer intercepts file data paths and applies RC4 transformation on the fly.

Key design elements:

  1. Mount point exposes standard POSIX interfaces; directory metadata is cached locally with TTL to reduce S3 calls (consistent with s3fs practices) [3].
  2. Read path: on file open/read, fetch object (or range) from S3 via s3fs; pass ciphertext through RC4 decryption stream before returning to the application.
  3. Write path: buffer writes locally; on file close or sync, apply RC4 encryption and upload the ciphertext as an S3 object. For partial writes, use ranged GET/PUT or multipart uploads as supported by s3fs.
  4. Change detection: use S3 object versioning or polling of bucket listings and ETags to discover remote changes and update local cache (push/poll hybrid) [1][3].
  5. Key management: a single symmetric key (derived from user-supplied passphrase or a local key file) is used for RC4; the key is not stored in S3. Recommend integrating KMS in production (see Future Improvements).

Integration and Results

Integration combined modified s3fs code with a wrapper encryption module implemented as a FUSE layer. The encryption layer hooks into read/write/flush operations. Basic functionality achieved:

  • Mounting an S3 bucket as a local directory and traversing files (POSIX semantics preserved) [3].
  • Local writes reflected in S3 as encrypted objects after flush/close operations.
  • Files uploaded via AWS console or other clients appear in the mountpoint after a short polling interval and are decrypted transparently when the mount obtains the object key.

Some limitations encountered:

  • Performance overhead due to encryption and S3 round-trips; metadata-heavy workloads suffer higher latency.
  • Conflict resolution for concurrent edits requires stronger locking or version-aware merge; current prototype uses last-writer-wins semantics.
  • RC4 is deprecated and insecure against modern attacks; used here only to meet the assignment constraint, with mitigation recommendations provided later [5][9].

Implementation Details

Two code locations were modified/added:

  1. s3fs modifications: added hooks to expose ETag/version metadata and to support ranged multipart uploads compatible with encrypted partial writes. Also exported a configuration option to disable internal s3fs client-side encryption to allow our RC4 layer to handle content transformation [3].
  2. Encryption layer: implemented as a FUSE passthrough module written in C, linking against OpenSSL RC4 APIs. The module implements interceptors for open/read/write/flush/release. On writes, data buffers are passed to RC4_encrypt() before invoking s3fs write routines; on reads, RC4_decrypt() converts ciphertext back to plaintext before returning data to applications. The key is derived using PBKDF2 from a passphrase to avoid raw-key exposure [4].

Concurrency: file-locking semantics are supported via POSIX locks at the FUSE layer and coordinated via S3 object metadata to minimize overwrite races. Metadata and caching parameters were tuned to balance consistency and performance.

Security and RC4 Considerations

RC4 is included per the assignment, but it is vulnerable to multiple attacks and discouraged in real deployments; RFC 7465 prohibits RC4 for TLS for good reasons [5]. For production, replace RC4 with AES-GCM or use client-side envelope encryption with AWS KMS for stronger confidentiality and integrity guarantees [1][4][8].

Future Improvements

  • Migrate from RC4 to AES-GCM or ChaCha20-Poly1305 for authenticated encryption and integrity protection [4].
  • Integrate AWS KMS for key management and rotate keys safely; support per-file encryption keys (envelope encryption) [1][8].
  • Implement real-time change notification using S3 Event Notifications and an SQS/SNS listener to reduce polling latency [1].
  • Enhance conflict resolution with optimistic locking and merge strategies or leverage S3 object versioning to detect and resolve concurrent writes.
  • Performance tuning: client-side write coalescing, adaptive caching, and multipart upload heuristics to improve throughput on large files [3].

Summary and Lessons Learned

The project demonstrates a working prototype for an S3-backed, mountable Linux file system with transparent encryption. Using existing components (FUSE, s3fs, OpenSSL) accelerated development; however, integration required careful handling of metadata, caching, and partial writes. The principal tradeoffs are performance vs. consistency and the need to use secure, modern encryption primitives rather than RC4. The stackable design proved effective for layering functionality: the encryption module cleanly separated concerns from S3 integration, enabling future cipher changes with minimal S3-specific code modifications.

References

  1. Amazon Web Services. Amazon Simple Storage Service (S3) Documentation. https://docs.aws.amazon.com/s3/ (accessed 2024).
  2. libfuse — Filesystem in Userspace. https://github.com/libfuse/libfuse (accessed 2024).
  3. s3fs-fuse project. s3fs on GitHub: https://github.com/s3fs-fuse/s3fs-fuse (accessed 2024).
  4. OpenSSL Project. OpenSSL Cryptography and SSL/TLS Toolkit. https://www.openssl.org/ (accessed 2024).
  5. IETF. RFC 7465: Prohibiting RC4 Cipher Suites. https://tools.ietf.org/html/rfc7465 (2015).
  6. S3QL project: A full-featured file system for online data storage. https://www.s3ql.org/ (accessed 2024).
  7. Zadok, E., & Nieh, J. FiST: A language for stackable file systems. (Paper and project overview). https://eazedok.github.io/ (accessed 2024).
  8. AWS Key Management Service (KMS) — Best practices and envelope encryption. https://docs.aws.amazon.com/kms/ (accessed 2024).
  9. B. Schneier, Applied Cryptography (for background on stream ciphers and modern alternates). Wiley, 1996.
  10. Amazon S3 Event Notifications and SQS/SNS integration (for change propagation). https://docs.aws.amazon.com/AmazonS3/latest/userguide/NotificationHowTo.html (accessed 2024).

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