Overview
ISO/IEC TR 24731-1:2007 is a technical report developed by ISO and IEC that specifies extensions to the C library, in support of safer and more secure programming. This standard offers a set of bounds-checking interfaces as alternatives to the traditional C library functions defined in ISO/IEC 9899:1999 (the C99 Standard). It mitigates common programming errors, such as buffer overflows, by requiring output buffers to be validated for size before operations are performed. Functions conforming to this standard indicate failures (such as when insufficient buffer is detected) and can optionally call a "runtime-constraint handler" to facilitate structured error reporting. A further benefit provided by these interfaces is improved re-entrancy: functions never return pointers to static, function-owned objects. These measures collectively strengthen software security and reliability when writing C code.
Key Topics
- Bounds-checking functions: Alternative functions in the C library that enforce strict validation of output buffer sizes, preventing data from being written beyond allocated memory.
- Runtime-constraint handling: Built-in mechanisms for reporting violations of runtime-constraints, such as invoking a user-defined handler if a function call fails its safety checks.
- Null termination: String results from these functions are always null-terminated, reducing typical errors seen in classic C string handling.
- Re-entrancy improvements: Functions do not return pointers to static, internal objects, supporting safer multi-threaded and nested operations.
- Safer I/O operations: The standard addresses commonly exploited insecurities within input/output facilities of the C library.
- Macro and type extensions: Adds new types like
errno_t for error codes and rsize_t for size arguments, along with macros such as RSIZE_MAX to define supported maximum object sizes.
Applications
ISO/IEC TR 24731-1:2007 is highly relevant in any context that requires development of robust, secure, and portable C programs. Key areas of application include:
- System Software Development: Writing operating systems, device drivers, and embedded systems where memory safety and reliability are critical.
- Security-sensitive Programming: Preventing common vulnerabilities like buffer overflows in network services, authentication code, and trusted computing environments.
- Enterprise and Mission-Critical Applications: Ensuring the integrity of data processing in domains such as finance, healthcare, and industrial control.
- Compiler and Library Implementations: Providing toolchain vendors with standardized, safer alternatives to legacy C library functions.
- Legacy Code Modernization: Refactoring or extending older codebases to comply with modern security best practices without sacrificing compatibility.
Related Standards
- ISO/IEC 9899:1999: The C programming language standard which serves as the foundation for TR 24731-1 extensions.
- ISO/IEC 9899:1999/Cor.1:2001 and Cor.2:2004: Technical corrigenda that update and clarify the C99 Standard.
- ISO/IEC 2382-1: Fundamental terms of information technology vocabulary, referenced for definitions.
- ISO 31-11: Provides mathematical symbols and signs relevant to technical documentation.
- Other C Library Extensions or Security Standards: While TR 24731-1 focuses on bounds-checking, its approach aligns with broader security-focused standards.
By adopting ISO/IEC TR 24731-1:2007, organizations and developers enhance both the safety and maintainability of C programs, effectively reducing the risk of vulnerabilities and runtime failures associated with improper buffer and string management in software development. This standard is essential for any safety- or security-critical applications using the C programming language.