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The CERT ® C Coding Standard: 98 Rules for Developing Safe, Reliable, and Secure Systems, Second Edition

Book Description

“At Cisco, we have adopted the CERT C Coding Standard as the internal secure coding standard for all C developers. It is a core component of our secure development lifecycle. The coding standard described in this book breaks down complex software security topics into easy-to-follow rules with excellent real-world examples. It is an essential reference for any developer who wishes to write secure and resilient software in C and C++.”
—Edward D. Paradise, vice president, engineering, threat response, intelligence, and development, Cisco Systems


Secure programming in C can be more difficult than even many experienced programmers realize. To help programmers write more secure code, The CERT® C Coding Standard, Second Edition, fully documents the second official release of the CERT standard for secure coding in C. The rules laid forth in this new edition will help ensure that programmers’ code fully complies with the new C11 standard; it also addresses earlier versions, including C99.


The new standard itemizes those coding errors that are the root causes of current software vulnerabilities in C, prioritizing them by severity, likelihood of exploitation, and remediation costs. Each of the text’s 98 guidelines includes examples of insecure code as well as secure, C11-conforming, alternative implementations. If uniformly applied, these guidelines will eliminate critical coding errors that lead to buffer overflows, format-string vulnerabilities, integer overflow, and other common vulnerabilities.

This book reflects numerous experts’ contributions to the open development and review of the rules and recommendations that comprise this standard.

Coverage includes

  • Preprocessor

  • Declarations and Initialization

  • Expressions

  • Integers

  • Floating Point

  • Arrays

  • Characters and Strings

  • Memory Management

  • Input/Output

  • Environment

  • Signals

  • Error Handling

  • Concurrency

  • Miscellaneous Issues

  • Table of Contents

    1. About This eBook
    2. Title Page
    3. Copyright Page
    4. Dedication Page
    5. Contents
    6. Preface
      1. Scope
      2. Who Should Read This Book
      3. History
      4. ISO/IEC TS 17961 C Secure Coding Rules
      5. Tool Selection and Validation
      6. Taint Analysis
      7. Rules versus Recommendations
      8. Usage
      9. Conformance Testing
      10. System Qualities
      11. How This Book Is Organized
      12. Automatically Generated Code
      13. Government Regulations
    7. Acknowledgments
    8. Contributors
    9. About the Author
    10. Chapter 1. Preprocessor (PRE)
      1. PRE30-C. Do not create a universal character name through concatenation
      2. PRE31-C. Avoid side effects in arguments to unsafe macros
      3. PRE32-C. Do not use preprocessor directives in invocations of function-like macros
    11. Chapter 2. Declarations and Initialization (DCL)
      1. DCL30-C. Declare objects with appropriate storage durations
      2. DCL31-C. Declare identifiers before using them
      3. DCL36-C. Do not declare an identifier with conflicting linkage classifications
      4. DCL37-C. Do not declare or define a reserved identifier
      5. DCL38-C. Use the correct syntax when declaring a flexible array member
      6. DCL39-C. Avoid information leakage in structure padding
      7. DCL40-C. Do not create incompatible declarations of the same function or object
      8. DCL41-C. Do not declare variables inside a switch statement before the first case label
    12. Chapter 3. Expressions (EXP)
      1. EXP30-C. Do not depend on the order of evaluation for side effects
      2. EXP32-C. Do not access a volatile object through a nonvolatile reference
      3. EXP33-C. Do not read uninitialized memory
      4. EXP34-C. Do not dereference null pointers
      5. EXP35-C. Do not modify objects with temporary lifetime
      6. EXP36-C. Do not cast pointers into more strictly aligned pointer types
      7. EXP37-C. Call functions with the correct number and type of arguments
      8. EXP39-C. Do not access a variable through a pointer of an incompatible type
      9. EXP40-C. Do not modify constant objects
      10. EXP42-C. Do not compare padding data
      11. EXP43-C. Avoid undefined behavior when using restrict-qualified pointers
      12. EXP44-C. Do not rely on side effects in operands to sizeof, _Alignof, or _Generic
      13. EXP45-C. Do not perform assignments in selection statements
    13. Chapter 4. Integers (INT)
      1. INT30-C. Ensure that unsigned integer operations do not wrap
      2. INT31-C. Ensure that integer conversions do not result in lost or misinterpreted data
      3. INT32-C. Ensure that operations on signed integers do not result in overflow
      4. INT33-C. Ensure that division and remainder operations do not result in divide-by-zero errors
      5. INT34-C. Do not shift an expression by a negative number of bits or by greater than or equal to the number of bits that exist in the operand
      6. INT35-C. Use correct integer precisions
      7. INT36-C. Converting a pointer to integer or integer to pointer
    14. Chapter 5. Floating Point (FLP)
      1. FLP30-C. Do not use floating-point variables as loop counters
      2. FLP32-C. Prevent or detect domain and range errors in math functions
      3. FLP34-C. Ensure that floating-point conversions are within range of the new type
      4. FLP36-C. Preserve precision when converting integral values to floating-point type
    15. Chapter 6. Arrays (ARR)
      1. ARR30-C. Do not form or use out-of-bounds pointers or array subscripts
      2. ARR32-C. Ensure size arguments for variable length arrays are in a valid range
      3. ARR36-C. Do not subtract or compare two pointers that do not refer to the same array
      4. ARR37-C. Do not add or subtract an integer to a pointer to a non-array object
      5. ARR38-C. Guarantee that library functions do not form invalid pointers
      6. ARR39-C. Do not add or subtract a scaled integer to a pointer
    16. Chapter 7. Characters and Strings (STR)
      1. STR30-C. Do not attempt to modify string literals
      2. STR31-C. Guarantee that storage for strings has sufficient space for character data and the null terminator
      3. STR32-C. Do not pass a non-null-terminated character sequence to a library function that expects a string
      4. STR34-C. Cast characters to unsigned char before converting to larger integer sizes
      5. STR37-C. Arguments to character handling functions must be representable as an unsigned char
      6. STR38-C. Do not confuse narrow and wide character strings and functions
    17. Chapter 8. Memory Management (MEM)
      1. MEM30-C. Do not access freed memory
      2. MEM31-C. Free dynamically allocated memory when no longer needed
      3. MEM33-C. Allocate and copy structures containing a flexible array member dynamically
      4. MEM34-C. Only free memory allocated dynamically
      5. MEM35-C. Allocate sufficient memory for an object
      6. MEM36-C. Do not modify the alignment of objects by calling realloc()
    18. Chapter 9. Input/Output (FIO)
      1. FIO30-C. Exclude user input from format strings
      2. FIO31-C. Do not open a file that is already open
      3. FIO32-C. Do not perform operations on devices that are only appropriate for files
      4. FIO34-C. Distinguish between characters read from a file and EOF or WEOF
      5. FIO37-C. Do not assume that fgets() or fgetws() returns a nonempty string when successful
      6. FIO38-C. Do not copy a FILE object
      7. FIO39-C. Do not alternately input and output from a stream without an intervening flush or positioning call
      8. FIO40-C. Reset strings on fgets() or fgetws() failure
      9. FIO41-C. Do not call getc(), putc(), getwc(), or putwc() with a stream argument that has side effects
      10. FIO42-C. Close files when they are no longer needed
      11. FIO44-C. Only use values for fsetpos() that are returned from fgetpos()
      12. FIO45-C. Avoid TOCTOU race conditions while accessing files
      13. FIO46-C. Do not access a closed file
      14. FIO47-C. Use valid format strings
    19. Chapter 10. Environment (ENV)
      1. ENV30-C. Do not modify the object referenced by the return value of certain functions
      2. ENV31-C. Do not rely on an environment pointer following an operation that may invalidate it
      3. ENV32-C. All exit handlers must return normally
      4. ENV33-C. Do not call system()
      5. ENV34-C. Do not store pointers returned by certain functions
    20. Chapter 11. Signals (SIG)
      1. SIG30-C. Call only asynchronous-safe functions within signal handlers
      2. SIG31-C. Do not access shared objects in signal handlers
      3. SIG34-C. Do not call signal() from within interruptible signal handlers
      4. SIG35-C. Do not return from a computational exception signal handler
    21. Chapter 12. Error Handling (ERR)
      1. ERR30-C. Set errno to zero before calling a library function known to set errno, and check errno only after the function returns a value indicating failure
      2. ERR32-C. Do not rely on indeterminate values of errno
      3. ERR33-C. Detect and handle standard library errors
    22. Chapter 13. Concurrency (CON)
      1. CON30-C. Clean up thread-specific storage
      2. CON31-C. Do not destroy a mutex while it is locked
      3. CON32-C. Prevent data races when accessing bit-fields from multiple threads
      4. CON33-C. Avoid race conditions when using library functions
      5. CON34-C. Declare objects shared between threads with appropriate storage durations
      6. CON35-C. Avoid deadlock by locking in a predefined order
      7. CON36-C. Wrap functions that can spuriously wake up in a loop
      8. CON37-C. Do not call signal() in a multithreaded program
      9. CON38-C. Preserve thread-safety and liveness when using condition variables
      10. CON39-C. Do not join or detach a thread that was previously joined or detached
      11. CON40-C. Do not refer to an atomic variable twice in an expression
      12. CON41-C. Wrap functions that can fail spuriously in a loop
    23. Chapter 14. Miscellaneous (MSC)
      1. MSC30-C. Do not use the rand() function for generating pseudorandom numbers
      2. MSC32-C. Properly seed pseudorandom number generators
      3. MSC33-C. Do not pass invalid data to the asctime() function
      4. MSC37-C. Ensure that control never reaches the end of a non-void function
      5. MSC38-C. Do not treat a predefined identifier as an object if it might only be implemented as a macro
      6. MSC39-C. Do not call va_arg() on a va_list that has an indeterminate value
      7. MSC40-C. Do not violate constraints
    24. Appendix A. Glossary
    25. Appendix B. Undefined Behavior
    26. Appendix C. Unspecified Behavior
    27. Bibliography
    28. Index