Linux File System Architecture

Linux File System Architecture from a cybersecurity perspective. Understand how hackers exploit file systems, key attack vectors like privilege escalation & rootkits, and best practices to secure Linux systems.

Linux File System Architecture Introduction

Linux file system is a critical component of the operating system that defines how data is stored, accessed, and managed. It follows a hierarchical directory structure and supports various file systems, each optimized for specific use cases. Understanding the Linux file system is essential for system administrators, cybersecurity experts, and developers.

The architecture is divided into two main sections:

1. User Space
2. Kernel Space

User Space

This is where applications and programs interact with the file system using system calls.

User Applications

• Applications such as text editors, browsers, and security tools (e.g., Nmap, Metasploit) interact with files stored in the Linux file system.
• Malware or exploits can manipulate file access through vulnerabilities in user applications.

GNU C Library (glibc)

• Acts as an intermediary between user applications and the system call interface.
• Provides standard APIs for system calls (e.g., open(), read(), write(), close()).
• Attackers often exploit vulnerabilities in glibc (e.g., buffer overflows) to execute arbitrary code.

Kernel Space

This is the core of the Linux file system, handling storage, access, and security.

System Call Interface

• Converts user-space requests into kernel-level operations.
• System calls like execve() are commonly targeted in privilege escalation attacks.

Virtual File System (VFS)

• Acts as an abstraction layer for different file systems (ext4, NTFS, FAT32).
• Ensures uniform access regardless of the underlying storage format.
• Attackers often target VFS to manipulate file system permissions.

Inode Cache & Directory Cache

• Inode Cache: Stores metadata (e.g., file size, owner, permissions).
  • Attackers might modify inodes to change file ownership (chown) or permissions (chmod).
• Directory Cache: Speeds up directory lookups.
  • Malware may manipulate directory caches to hide files (rootkits).

Individual File Systems

• Handles specific file system operations (e.g., journaling in ext4).
• Exploits like “dirty COW” (CVE-2016-5195) target file system vulnerabilities.

Buffer Cache

• Temporarily stores frequently accessed data to improve performance.
• Attackers can manipulate buffer caches to persist malicious data.

Device Drivers

• Interfaces between hardware storage (HDDs, SSDs, USBs) and the file system.
• USB-based attacks (e.g., BadUSB) exploit vulnerabilities in device drivers.

Cybersecurity Implications & Attack Vectors

1. Privilege Escalation – Exploiting system calls to gain root access.
2. Rootkits & Hidden Files – Manipulating inode cache and directory cache.
3. Ransomware Attacks – Encrypting files and manipulating the file system.
4. Forensic Investigations – Analyzing file system changes to detect cyber threats.
5. File Integrity Monitoring (FIM) – Tools like Tripwire detect unauthorized file modifications.

Conclution

Understanding Linux File System Architecture helps ethical hackers and cybersecurity experts:

• Secure file access and prevent unauthorized modifications.
• Detect malware that exploits file system vulnerabilities.
• Implement robust forensic techniques to investigate cyber incidents.

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