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sec-design.md

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Okay, let's create a design document for the libcsptr project.

BUSINESS POSTURE

Business Priorities and Goals:

  • Provide a simple, header-only C library for counted string pointers.
  • Enhance code safety and readability by managing string lifetimes.
  • Offer a lightweight alternative to more complex string management solutions.
  • Minimize external dependencies to ensure easy integration into various projects.
  • Reduce memory leaks.

Most Important Business Risks:

  • Adoption Risk: The library may not gain traction if it's perceived as too niche, overly complex, or if superior alternatives exist.
  • Maintenance Risk: As a single-developer, header-only library, long-term maintenance and support could be a challenge. Lack of updates could lead to incompatibility with newer C standards or compiler versions.
  • Security Risk: While aiming for safety, undiscovered bugs or misuse of the library could introduce vulnerabilities, especially related to string manipulation and memory management.
  • Integration Risk: Compatibility issues with existing codebases or specific compiler configurations could hinder adoption.

SECURITY POSTURE

Existing Security Controls:

  • security control: The library's core design, using counted string pointers, inherently mitigates some common string handling errors like buffer overflows (when used correctly). Described in library header file.
  • security control: The library is self-contained (header-only) reducing external dependencies and thus the attack surface. Described in README.md.
  • security control: Code is publicly available on GitHub, allowing for community review and potential identification of vulnerabilities. Described in README.md.

Accepted Risks:

  • accepted risk: The library is provided "as is," with no warranty. Users assume responsibility for its proper use and integration.
  • accepted risk: The library does not encrypt or protect the content of the strings. It only manages their memory.
  • accepted risk: The library relies on the user to correctly use the provided functions. Incorrect usage can still lead to memory errors.
  • accepted risk: There is no formal security audit process in place.

Recommended Security Controls:

  • security control: Integrate static analysis tools (e.g., clang-tidy, Coverity) into the development workflow to catch potential bugs early.
  • security control: Add comprehensive unit tests, including edge cases and potential misuse scenarios, to ensure robustness.
  • security control: Consider using fuzzing techniques to test the library's resilience against unexpected inputs.
  • security control: Provide clear and detailed documentation on secure usage patterns, including examples of both correct and incorrect usage.
  • security control: Establish a security reporting process (e.g., a SECURITY.md file in the repository) to allow users to responsibly disclose vulnerabilities.

Security Requirements:

  • Authentication: Not applicable, as the library doesn't handle authentication.
  • Authorization: Not applicable, as the library doesn't handle authorization.
  • Input Validation: The library should internally validate its inputs (e.g., checking for NULL pointers, valid lengths) to prevent crashes or undefined behavior. It should not, however, attempt to validate the content of the strings, as that is application-specific.
  • Cryptography: Not applicable, as the library is not intended for cryptographic operations. If string content needs encryption, that should be handled by a separate, dedicated library.

DESIGN

C4 CONTEXT

graph LR
    User["User/Application"] -- "Uses" --> Libcsptr["libcsptr\n(Counted String Pointer Library)"]
    Libcsptr -- "Relies on" --> StandardCLibrary["Standard C Library\n(libc)"]
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Context Diagram Element Descriptions:

  • Element:

    • Name: User/Application
    • Type: External Entity (Software System)
    • Description: Any C application or library that utilizes libcsptr for string management.
    • Responsibilities: Calls libcsptr functions to create, manipulate, and release counted string pointers.
    • Security controls: Relies on libcsptr for safe string handling; implements its own security measures for other aspects of the application.

  • Element:

    • Name: libcsptr
    • Type: Software System (Library)
    • Description: The libcsptr library itself, providing counted string pointer functionality.
    • Responsibilities: Manages the allocation, deallocation, and reference counting of string data. Provides functions for string manipulation.
    • Security controls: Implements internal checks to prevent common string handling errors. Relies on the standard C library for underlying memory management.

  • Element:

    • Name: Standard C Library (libc)
    • Type: External Entity (Software System)
    • Description: The standard C library, providing fundamental functions like malloc, free, strlen, etc.
    • Responsibilities: Provides basic system-level functionality, including memory management.
    • Security controls: Assumed to be a well-tested and secure component of the operating system. libcsptr relies on its correct behavior.

C4 CONTAINER

Since libcsptr is a header-only library, the container diagram is essentially the same as the context diagram. There are no separate deployable units.

graph LR
    User["User/Application"] -- "Uses" --> Libcsptr["libcsptr\n(Counted String Pointer Library)"]
    Libcsptr -- "Relies on" --> StandardCLibrary["Standard C Library\n(libc)"]
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Container Diagram Element Descriptions:

  • Element:

    • Name: User/Application
    • Type: External Entity (Software System)
    • Description: Any C application or library that utilizes libcsptr for string management.
    • Responsibilities: Calls libcsptr functions to create, manipulate, and release counted string pointers.
    • Security controls: Relies on libcsptr for safe string handling; implements its own security measures for other aspects of the application.

  • Element:

    • Name: libcsptr
    • Type: Software System (Library)
    • Description: The libcsptr library itself, providing counted string pointer functionality.
    • Responsibilities: Manages the allocation, deallocation, and reference counting of string data. Provides functions for string manipulation.
    • Security controls: Implements internal checks to prevent common string handling errors. Relies on the standard C library for underlying memory management.

  • Element:

    • Name: Standard C Library (libc)
    • Type: External Entity (Software System)
    • Description: The standard C library, providing fundamental functions like malloc, free, strlen, etc.
    • Responsibilities: Provides basic system-level functionality, including memory management.
    • Security controls: Assumed to be a well-tested and secure component of the operating system. libcsptr relies on its correct behavior.

DEPLOYMENT

Deployment Solutions:

  1. Direct Inclusion: The user directly includes the csptr.h header file in their project's source code. This is the primary and recommended deployment method.
  2. System-Wide Installation: The user could copy csptr.h to a system-wide include directory (e.g., /usr/local/include). This is generally discouraged as it can lead to version conflicts and makes updates less manageable.
  3. Package Manager: While not currently supported, the library could be packaged for various C package managers (e.g., Conan, vcpkg). This would simplify integration into larger projects.

Chosen Deployment Solution (Detailed): Direct Inclusion

graph LR
    Developer["Developer"] -- "Copies csptr.h" --> ProjectSource["Project Source Code"]
    ProjectSource -- "Includes csptr.h" --> Compiler["C Compiler"]
    Compiler -- "Produces" --> Executable["Executable/Library"]
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Deployment Diagram Element Descriptions:

  • Element:

    • Name: Developer
    • Type: Person
    • Description: The developer integrating libcsptr into their project.
    • Responsibilities: Obtains the csptr.h file and places it in the appropriate location within their project.
    • Security controls: Ensures the integrity of the csptr.h file (e.g., by verifying its source or checksum).

  • Element:

    • Name: Project Source Code
    • Type: Code
    • Description: The source code of the project using libcsptr.
    • Responsibilities: Includes the csptr.h header file and uses its functions.
    • Security controls: Relies on the developer to correctly use libcsptr and to implement other necessary security measures.

  • Element:

    • Name: C Compiler
    • Type: Tool
    • Description: The C compiler used to build the project (e.g., GCC, Clang).
    • Responsibilities: Compiles the project source code, including libcsptr, into an executable or library.
    • Security controls: Relies on the compiler's own security features and configuration.

  • Element:

    • Name: Executable/Library
    • Type: Artifact
    • Description: The compiled output of the project, incorporating libcsptr.
    • Responsibilities: Executes the project's logic, including libcsptr's string management functions.
    • Security controls: Inherits the security characteristics of libcsptr and the project's code.

BUILD

Build Process:

Since libcsptr is a header-only library, there is no separate build process for the library itself. The "build" process is simply the compilation of the user's project that includes csptr.h. However, we can discuss the build process of a project using libcsptr, and how security can be integrated into that process.

graph LR
    Developer["Developer"] -- "Writes Code" --> SourceCode["Source Code\n(including csptr.h)"]
    SourceCode -- "Commits to" --> GitRepository["Git Repository"]
    GitRepository -- "Triggers" --> CI["CI System\n(e.g., GitHub Actions)"]
    CI -- "Runs Tests" --> TestResults["Test Results"]
    CI -- "Runs Static Analysis" --> StaticAnalysisResults["Static Analysis Results"]
    CI -- "Compiles" --> Executable["Executable/Library"]
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Build Process Description:

  1. Development: The developer writes code, including the csptr.h header file and using its functions.
  2. Commit: The code is committed to a Git repository (e.g., GitHub).
  3. Continuous Integration (CI): A CI system (e.g., GitHub Actions, Jenkins) is triggered by the commit.
  4. Testing: The CI system runs unit tests, including tests specifically designed for libcsptr usage.
  5. Static Analysis: The CI system runs static analysis tools (e.g., clang-tidy, Coverity) to identify potential bugs and security vulnerabilities.
  6. Compilation: If tests and static analysis pass, the CI system compiles the code into an executable or library.

Security Controls in Build Process:

  • security control: Version Control (Git): Tracks changes to the code, allowing for auditing and rollbacks.
  • security control: CI System: Automates the build, test, and analysis process, ensuring consistency and repeatability.
  • security control: Unit Tests: Verify the correct behavior of the code, including libcsptr usage.
  • security control: Static Analysis: Detects potential bugs and security vulnerabilities before runtime.
  • security control: Dependency Management: (Potentially, if a package manager is used) Ensures that dependencies are tracked and updated securely.

RISK ASSESSMENT

Critical Business Processes:

  • The primary business process is providing reliable and safe string management within C applications. The library's success depends on its ability to perform this function correctly and efficiently.

Data Protection:

  • Data: The library handles string data, which can range in sensitivity from non-sensitive (e.g., configuration settings) to highly sensitive (e.g., user input, passwords, API keys).
  • Sensitivity: The library itself does not classify or treat string data differently based on sensitivity. This is the responsibility of the application using the library. The library should aim to prevent vulnerabilities that could lead to any string data being exposed or corrupted (e.g., buffer overflows, use-after-free errors).

QUESTIONS & ASSUMPTIONS

Questions:

  • Are there any specific performance requirements or constraints for the library?
  • Are there any target platforms or compiler versions that need to be specifically supported or excluded?
  • Is there a plan for long-term maintenance and support of the library?
  • What level of code coverage is desired for unit tests?
  • Are there any existing coding style guidelines or conventions that should be followed?

Assumptions:

  • BUSINESS POSTURE: The primary goal is to create a useful and safe library, prioritizing correctness and simplicity over extensive features.
  • SECURITY POSTURE: The developer is aware of basic C security best practices and aims to avoid common vulnerabilities. However, no formal security expertise is assumed.
  • DESIGN: The library will remain header-only and will not introduce any external dependencies beyond the standard C library. The user is responsible for understanding and correctly using the library's functions. The user is responsible for handling any sensitive data appropriately.