CERT C Secure Coding Standard, The

“I’m an enthusiastic supporter of the CERT Secure Coding Initiative. Programmers have lots of sources of advice on correctness, clarity, maintainability, performance, and even safety. Advice on how specific language features affect security has been missing. The CERT ® C Secure Coding Standard fills this need.” –Randy Meyers, Chairman of ANSI C “For years we have relied upon the CERT/CC to publish advisories documenting an endless stream of security problems. Now CERT has embodied the advice of leading technical experts to give programmers and managers the practical guidance needed to avoid those problems in new  applications and to help secure legacy systems. Well done!” –Dr. Thomas Plum, founder of Plum Hall, Inc. “Connectivity has sharply increased the need for secure, hacker-safe applications. By combining this CERT standard with other safety guidelines, customers gain all-round protection and approach the goal of zero-defect software.” –Chris Tapp, Field Applications Engineer, LDRA Ltd. “I’ve found this standard to be an indispensable collection of expert information on exactly how modern software systems fail in practice. It is the perfect place to start for establishing internal secure coding guidelines. You won’t find this information elsewhere, and, when it comes to software security, what you don’t know is often exactly what hurts you.” –John McDonald, coauthor of The Art of Software Security Assessment Software security has major implications for the operations and assets of organizations, as well as for the welfare of individuals. To create secure software, developers must know where the dangers lie. Secure programming in C can be more difficult than even many experienced  programmers believe. This book is an essential desktop reference documenting the first official release of  The CERT® C Secure Coding Standard. The standard itemizes those coding errors that are the root causes of software vulnerabilities in C and prioritizes them by severity, likelihood of exploitation, and remediation costs. Each guideline provides examples of insecure code as well as secure, alternative implementations. If uniformly applied, these guidelines will eliminate the critical coding errors that lead to buffer overflows, format string vulnerabilities, integer  overflow, and other common software vulnerabilities.

Table of Contents:
Preface               xvii Acknowledgments     xxxi About the Author     xxxiii Chapter 1: Using This Standard     1 System Qualities           1 Automatically Generated Code         2 Compliance             3 Chapter 2: Preprocessor (PRE) 5 PRE00-C. Prefer inline or static functions to function-like macros          6 PRE01-C. Use parentheses within macros around parameter names          11 PRE02-C. Macro replacement lists should be parenthesized        13 PRE03-C. Prefer type definitions to defines for encoding types          15 PRE04-C. Do not reuse a standard header file name           16 PRE05-C. Understand macro replacement when concatenating tokens or performing stringification     18 PRE06-C. Enclose header files in an inclusion guard         21 PRE07-C. Avoid using repeated question marks           22 PRE08-C. Guarantee that header file names are unique          24 PRE09-C. Do not replace secure functions with less secure functions       26 PRE10-C. Wrap multistatement macros in a do-while loop          27 PRE30-C. Do not create a universal character name through concatenation        29 PRE31-C. Never invoke an unsafe macro with arguments containing assignment, increment, decrement, volatile access, or function call        30 Chapter 3: Declarations and Initialization (DCL)       33 DCL00-C. const-qualify immutable objects      35 DCL01-C. Do not reuse variable names in subscopes         36 DCL02-C. Use visually distinct identifiers      38 DCL03-C. Use a static assertion to test the value of a constant expression      39 DCL04-C. Do not declare more than one variable per declaration      42 DCL05-C. Use type definitions to improve code readability      44 DCL06-C. Use meaningful symbolic constants to represent literal values in program logic      45 DCL07-C. Include the appropriate type information in function declarators        51 DCL08-C. Properly encode relationships in constant definitions           54 DCL09-C. Declare functions that return an errno error code with a return type of errno_t       57 DCL10-C. Maintain the contract between the writer and caller of variadic functions         59 DCL11-C. Understand the type issues associated with variadic functions          62 DCL12-C. Implement abstract data types using opaque types        64 DCL13-C. Declare function parameters that are pointers to values not changed by the function as const             66 DCL14-C. Do not make assumptions about the order of global variable initialization across translation units             69 DCL15-C. Declare objects that do not need external linkage with the storage-class specifier static        70 DCL30-C. Declare objects with appropriate storage durations        72 DCL31-C. Declare identifiers before using them          74 DCL32-C. Guarantee that mutually visible identifiers are unique        78 DCL33-C. Ensure that restrict-qualified source and destination pointers in function arguments do not reference overlapping objects        80 DCL34-C. Use volatile for data that cannot be cached       82 DCL35-C. Do not convert a function using a type that does not match the function definition         84 DCL36-C. Do not declare an identifier with conflicting linkage classifications        87 Chapter 4: Expressions (EXP)        91 EXP00-C. Use parentheses for precedence of operation           93 EXP01-C. Do not take the size of a pointer to determine the size of the pointed-to type     95 EXP02-C. Be aware of the short-circuit behavior of the logical AND and OR operators      96 EXP03-C. Do not assume the size of a structure is the sum of the sizes of its members      98 EXP04-C. Do not perform byte-by-byte comparisons between structures      100 EXP05-C. Do not cast away a const qualification        102 EXP06-C. Operands to the sizeof operator should not contain side effects           104 EXP07-C. Do not diminish the benefits of constants by assuming their values in expressions          105 EXP08-C. Ensure pointer arithmetic is used correctly           107 EXP09-C. Use sizeof to determine the size of a type or variable          109 EXP10-C. Do not depend on the order of evaluation of subexpressions or the order in which side effects take place         111 EXP11-C. Do not apply operators expecting one type to data of an incompatible type      114 EXP12-C. Do not ignore values returned by functions      118 EXP30-C. Do not depend on order of evaluation between sequence points      119 EXP31-C. Avoid side effects in assertions     122 EXP32-C. Do not cast away a volatile qualification     123 EXP33-C. Do not reference uninitialized memory     124 EXP34-C. Ensure a null pointer is not dereferenced     128 EXP35-C. Do not access or modify the result of a function call after a subsequent sequence point         129 EXP36-C. Do not convert pointers into more strictly aligned pointer types         131 EXP37-C. Call functions with the arguments intended by the API         133 EXP38-C. Do not call offsetof() on bit-field members or invalid types           135 Chapter 5: Integers (INT)        139 INT00-C. Understand the data model used by your implementation(s)        141 INT01-C. Use rsize_t or size_t for all integer values representing the size of an object        145 INT02-C. Understand integer conversion rules       149 INT03-C. Use a secure integer library       153 INT04-C. Enforce limits on integer values originating from untrusted sources      155 INT05-C. Do not use input functions to convert character data if they cannot handle all possible inputs       157 INT06-C. Use strtol() or a related function to convert a string token to an integer       159 INT07-C. Use only explicitly signed or unsigned char type for numeric values       162 INT08-C. Verify that all integer values are in range        164 INT09-C. Ensure enumeration constants map to unique values        167 INT10-C. Do not assume a positive remainder when using the % operator       168 INT11-C. Take care when converting from pointer to integer or integer to pointer       170 INT12-C. Do not make assumptions about the type of a plain int bit-field when used in an expression        172 INT13-C. Use bitwise operators only on unsigned operands         174 INT14-C. Avoid performing bitwise and arithmetic operations on the same data         175 INT15-C. Use intmax_t or uintmax_t for formatted I/O on programmer-defined integer types      178 INT30-C. Ensure that unsigned integer operations do not wrap         181 INT31-C. Ensure that integer conversions do not result in lost or misinterpreted data        186 INT32-C. Ensure that operations on signed integers do not result in overflow       191 INT33-C. Ensure that division and modulo operations do not result in divide-by-zero errors     201 INT34-C. Do not shift a negative number of bits or more bits than exist in the operand    203 INT35-C. Evaluate integer expressions in a larger size before comparing or assigning to that size          207 Chapter 6: Floating Point (FLP)       211 FLP00-C. Understand the limitations of floating-point numbers       212 FLP01-C. Take care in rearranging floating-point expressions         214 FLP02-C. Consider avoiding floating-point numbers when precise computation is needed     215 FLP03-C. Detect and handle floating-point errors     218 FLP30-C. Do not use floating-point variables as loop counters     224 FLP31-C. Do not call functions expecting real values with complex values     226 FLP32-C. Prevent or detect domain and range errors in math functions     227 FLP33-C. Convert integers to floating point for floating-point operations     234 FLP34-C. Ensure that floating-point conversions are within range of the new type       236 Chapter 7: Arrays (ARR)         241 ARR00-C. Understand how arrays work        242 ARR01-C. Do not apply the sizeof operator to a pointer when taking the size of an array       245 ARR02-C. Explicitly specify array bounds, even if implicitly defined by an initializer     248 ARR30-C. Guarantee that array indices are within the valid range      250 ARR31-C. Use consistent array notation across all source files      251 ARR32-C. Ensure size arguments for variable length arrays are in a valid range      254 ARR33-C. Guarantee that copies are made into storage of sufficient size      255 ARR34-C. Ensure that array types in expressions are compatible      258 ARR35-C. Do not allow loops to iterate beyond the end of an array      259 ARR36-C. Do not subtract or compare two pointers that do not refer to the same array      261 ARR37-C. Do not add or subtract an integer to a pointer to a non-array object     263 ARR38-C. Do not add or subtract an integer to a pointer if the resulting value does not refer to a valid array element     265 Chapter 8: Characters and Strings (STR)        271 STR00-C. Represent characters using an appropriate type       273 STR01-C. Adopt and implement a consistent plan for managing strings      275 STR02-C. Sanitize data passed to complex subsystems      276 STR03-C. Do not inadvertently truncate a null-terminated byte string      280 STR04-C. Use plain char for characters in the basic character set      282 STR05-C. Use pointers to const when referring to string literals       284 STR06-C. Do not assume that strtok() leaves the parse string unchanged      286 STR07-C. Use TR 24731 for remediation of existing string manipulation code      288 STR08-C. Use managed strings for development of new string manipulation code      291 STR30-C. Do not attempt to modify string literals      293 STR31-C. Guarantee that storage for strings has sufficient space for character data and the null terminator      294 STR32-C. Null-terminate byte strings as required       299 STR33-C. Size wide character strings correctly      303 STR34-C. Cast characters to unsigned types before converting to larger integer sizes      305 STR35-C. Do not copy data from an unbounded source to a fixed-length array      307 STR36-C. Do not specify the bound of a character array initialized with a string literal     312 STR37-C. Arguments to character-handling functions must be representable as an unsigned char      314 Chapter 9: Memory Management (MEM)      317 MEM00-C. Allocate and free memory in the same module at the same level of abstraction    319 MEM01-C. Store a new value in pointers immediately after free()     322 MEM02-C. Immediately cast the result of a memory allocation function call into a pointer to the allocated type      324 MEM03-C. Clear sensitive information stored in reusable resources returned for reuse    328 MEM04-C. Do not perform zero-length allocations      332 MEM05-C. Avoid large stack allocations      335 MEM06-C. Ensure that sensitive data is not written out to disk     338 MEM07-C. Ensure that the arguments to calloc(), when multiplied, can be represented as a size_t      342 MEM08-C. Use realloc() only to resize dynamically allocated arrays       343 MEM09-C. Do not assume memory allocation routines initialize memory      346 MEM10-C. Use a pointer validation function       348 MEM30-C. Do not access freed memory       351 MEM31-C. Free dynamically allocated memory exactly once      353 MEM32-C. Detect and handle memory allocation errors      355 MEM33-C. Use the correct syntax for flexible array members      358 MEM34-C. Only free memory allocated dynamically      360 MEM35-C. Allocate sufficient memory for an object       362 Chapter 10: Input/Output (FIO)      367 FIO00-C. Take care when creating format strings      370 FIO01-C. Be careful using functions that use file names for identification      372 FIO02-C. Canonicalize path names originating from untrusted sources      374 FIO03-C. Do not make assumptions about fopen() and file creation      383 FIO04-C. Detect and handle input and output errors     386 FIO05-C. Identify files using multiple file attributes      389 FIO06-C. Create files with appropriate access permissions      394 FIO07-C. Prefer fseek() to rewind()      398 FIO08-C. Take care when calling remove() on an open file      399 FIO09-C. Be careful with binary data when transferring data across systems     401 FIO10-C. Take care when using the rename() function      403 FIO11-C. Take care when specifying the mode parameter of fopen()      407 FIO12-C. Prefer setvbuf() to setbuf()      408 FIO13-C. Never push back anything other than one read character      409 FIO14-C. Understand the difference between text mode and binary mode with file streams     411 FIO15-C. Ensure that file operations are performed in a secure directory    413 FIO16-C. Limit access to files by creating a jail     418 FIO30-C. Exclude user input from format strings     421 FIO31-C. Do not simultaneously open the same file multiple times     424 FIO32-C. Do not perform operations on devices that are only appropriate for files     426 FIO33-C. Detect and handle input output errors resulting in undefined behavior      431 FIO34-C. Use int to capture the return value of character I/O functions      436 FIO35-C. Use feof() and ferror() to detect end-of-file and file errors when sizeof(int) == sizeof(char)      438 FIO36-C. Do not assume a new-line character is read when using fgets()      440 FIO37-C. Do not assume character data has been read      442 FIO38-C. Do not use a copy of a FILE object for input and output      443 FIO39-C. Do not alternately input and output from a stream without an intervening flush or positioning call      444 FIO40-C. Reset strings on fgets() failure      446 FIO41-C. Do not call getc() or putc() with stream arguments that have side effects     448 FIO42-C. Ensure files are properly closed when they are no longer needed      450 FIO43-C. Do not create temporary files in shared directories      454 FIO44-C. Only use values for fsetpos() that are returned from fgetpos()         464 Chapter 11: Environment (ENV) 467 ENV00-C. Do not store the pointer to the string returned by getenv()      468 ENV01-C. Do not make assumptions about the size of an environment variable      474 ENV02-C. Beware of multiple environment variables with the same effective name      475 ENV03-C. Sanitize the environment when invoking external programs        478 ENV04-C. Do not call system() if you do not need a command processor      482 ENV30-C. Do not modify the string returned by getenv()       487 ENV31-C. Do not rely on an environment pointer following an operation that may invalidate it         489 ENV32-C. No atexit handler should terminate in any way other than by returning       494 Chapter 12: Signals (SIG)      499 SIG00-C. Mask signals handled by noninterruptible signal handlers      500 SIG01-C. Understand implementation-specific details regarding signal handler persistence    503 SIG02-C. Avoid using signals to implement normal functionality      507 SIG30-C. Call only asynchronous-safe functions within signal handlers      511 SIG31-C. Do not access or modify shared objects in signal handlers      517 SIG32-C. Do not call longjmp() from inside a signal handler      519 SIG33-C. Do not recursively invoke the raise() function      523 SIG34-C. Do not call signal() from within interruptible signal handlers     526 Chapter 13: Error Handling (ERR)     531 ERR00-C. Adopt and implement a consistent and comprehensive error-handling policy    533 ERR01-C. Use ferror() rather than errno to check for FILE stream errors     535 ERR02-C. Avoid in-band error indicators    537 ERR03-C. Use runtime-constraint handlers when calling functions defined by TR 24731-1     541 ERR04-C. Choose an appropriate termination strategy     544 ERR05-C. Application-independent code should provide error detection without dictating error handling     549 ERR06-C. Understand the termination behavior of assert() and abort()     556 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  558 ERR31-C. Do not redefine errno     563 ERR32-C. Do not rely on indeterminate values of errno     564 Chapter 14: Miscellaneous (MSC)     569 MSC00-C. Compile cleanly at high warning levels    570 MSC01-C. Strive for logical completeness     572 MSC02-C. Avoid errors of omission     574 MSC03-C. Avoid errors of addition     576 MSC04-C. Use comments consistently and in a readable fashion    578 MSC05-C. Do not manipulate time_t typed values directly     580 MSC06-C. Be aware of compiler optimization when dealing with sensitive data     582 MSC07-C. Detect and remove dead code     585 MSC08-C. Library functions should validate their parameters    588 MSC09-C. Character encoding: use subset of ASCII for safety     590 MSC10-C. Character encoding: UTF-8-related issues    594 MSC11-C. Incorporate diagnostic tests using assertions    597 MSC12-C. Detect and remove code that has no effect    598 MSC13-C. Detect and remove unused values     600 MSC14-C. Do not introduce unnecessary platform dependencies     602 MSC15-C. Do not depend on undefined behavior     604 MSC30-C. Do not use the rand() function for generating pseudorandom numbers     607 MSC31-C. Ensure that return values are compared against the proper type      610 Appendix: POSIX (POS)     613 POS00-C. Avoid race conditions with multiple threads     615 POS01-C. Check for the existence of links     617 POS02-C. Follow the principle of least privilege     620 POS30-C. Use the readlink() function properly     623 POS31-C. Do not unlock or destroy another thread’s mutex     625 POS32-C. Include a mutex when using bit-fields in a multithreaded environment    626 POS33-C. Do not use vfork()     629 POS34-C. Do not call putenv() with a pointer to an automatic variable as the argument     631 POS35-C. Avoid race conditions while checking for the existence of a symbolic link     633 POS36-C. Observe correct revocation order while relinquishing privileges     636 POS37-C. Ensure that privilege relinquishment is successful     637 Glossary     643 References     647 Index     659