Intro 1 - About

February 21, 2024

In the realm of Linux system administration, ensuring the security and integrity of your systems is paramount. One of the advanced toolsets at your disposal for achieving this is the fapolicy-analyzer tools, which are closely related to fapolicyd, the File Access Policy Daemon. This post is the first in a series that will be discussing the capabilities of the fapolicy-analyzer tools and how they can help achieve and maintain a secure file access policy.

The blog series starts here with a high level introduction and then proceeds into the essentials of the fapolicy-analyzer, discussing its purpose, how it complements fapolicyd, and along the way offering practical advice on how to effectively use it to bolster your system’s security.

The File Access Policy Analyzer #

The fapolicy-analyzer is a tool used within the fapolicyd ecosystem to enhance system security on Linux by controlling and analyzing file access based on predefined policies. It allows administrators and security professionals to examine existing file access policies to understand the rules in place and their impact on the system. Additionally, the fapolicy-analyzer can be used to test new policies in a non-intrusive manner, enabling fine-tuning before enforcement, ensuring that the policies are effective and do not disrupt legitimate system operations.

The capabilities of the fapolicy-analyzer include analyzing current file access policies, testing new policies before implementation, and providing insights into how policies affect system operations. By leveraging Rust’s modern tooling, cross-platform compatibility, and growing ecosystem, the development and maintenance of fapolicy-analyzer are streamlined, resulting in a robust and reliable tool that aligns well with the security and performance requirements of a file access policy analyzer.

The fapolicy-analyzer is a utility designed to work alongside fapolicyd, aimed at analyzing and managing file access policies within Linux environments. While fapolicyd enforces file access policies to prevent unauthorized file execution and access, fapolicy-analyzer serves as a powerful tool for auditing, testing, and refining these policies. It helps administrators understand the impact of their policies, identify potential security loopholes, and ensure compliance with organizational security standards.

Defining a File Access Policy #

A “file access policy” in the context of fapolicyd and fapolicy-analyzer revolves around the concept of trust and rules that govern file access and execution on a Linux system. These policies enhance system security by defining trusted sources and establishing rules that dictate how files from these sources can be accessed.

In fapolicyd, trust is a key concept, where files can be marked as trusted based on their origin, such as files from the system’s package manager or files with a valid digital signature. This trust designation helps in differentiating between files that are considered safe and those that might pose a risk. Individual trust entries are defined by the expected file size or sha256 hash of a file at a path, and a tuple of these values for each file is maintained in a database by fapolicyd.

The rules in the file access policy specify the conditions under which files can be accessed or executed. These rules can be based on various attributes, such as file paths, file types, and the trust level of the file. For example, a rule might allow the execution of all files in a specific directory if they are marked as trusted, while blocking the execution of untrusted files from the same directory. Rules are defined in a list that is evaulated sequentially, where the first matching rule wins and is executed. The resulting decision is passed on to fanotify which directs the kernel whether to allow or deny the file access request.

fapolicyd enforces these policies by monitoring file access requests and deciding whether to allow or deny them based on the rules and trust levels. fapolicy-analyzer is used to analyze these policies, helping administrators understand how the rules and trust designations affect file access on the system and enabling them to fine-tune the policies for optimal security and system functionality.

GTK3 Frontend, Rust Backend #

The fapolicy-analyzer GUI frontend is implemented in GTK3 which offers several advantages, particularly in terms of user interface design and integration with the Linux desktop environment. GTK3, being a native toolkit for GNOME, ensures that the application will have a consistent look and feel with other applications in the desktop environment, providing a seamless user experience. The rich set of widgets and tools available in GTK3 allows for the creation of intuitive and user-friendly interfaces, making it easier for administrators and security professionals to interact with the application, visualize policies, and analyze results. Additionally, GTK3 supports theming, which enables customization of the application’s appearance to match the user’s preferences or the system’s theme.

Implementing the fapolicy-analyzer in Rust offers several advantages, including memory safety, concurrency safety, and performance. Rust’s ownership model ensures memory safety without a garbage collector, reducing the risk of memory-related security vulnerabilities. Its type system and ownership model also prevent data races, making it easier to write safe concurrent code. Furthermore, Rust’s performance is comparable to C and C++, which is crucial for efficiently processing large sets of file access policies and logs.

A Summary of fapolicy-analyzer Tools #

The fapolicy-analyzer design is centered around configuration and analysis of the runtime behavior of fapolicyd.

The capabilities to do this are provided by a number of different tools arranged into views of the GUI application.

1. Rule editor with syntax highlighting, syntax validation, and policy linting
2. Trust database manager to synchronize what fapolicyd believes and what exists on disk
3. Log analyzer provides insight to help understand and tune fapolicyd runtime behavior
4. Disk access profiler to capture file access requests for an executing application
5. Configuration file editor for fapolicyd, with syntax validation and linting
6. DBUS based control of the fapolicyd daemon which is immune to bad policy lockout

Here is a screenshot of the GTK3 GUI displaying the rule editor.

We will discuss the rule editor in detail in a follow-up post.

Please watch for the next post in the series where we walk through the installation and configuration of the fapolicy-analyzer.

Additional information can be found in the fapolicy-analyzer user guide which is available on the GitHub Wiki and is also packaged in the RPM packages.