The CERT C Secure Coding Standard
Published on 23. October 2008
Book
Paperback/Softback
720 pages
978-0-321-56321-7 (ISBN)
Description
"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 (R) 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 (R) 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.
-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 (R) 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.
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Language
English
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New Jersey
United States
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Pearson Education (US)
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Professional and scholarly
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Height: 234 mm
Width: 178 mm
Thickness: 36 mm
Weight
1030 gr
ISBN-13
978-0-321-56321-7 (9780321563217)
Copyright in bibliographic data and cover images is held by Nielsen Book Services Limited or by the publishers or by their respective licensors: all rights reserved.
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Robert Seacord
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Robert C. Seacord leads the Secure Coding Initiative at the CERT at the Software Engineering Institute (SEI) in Pittsburgh, Pennsylvania. The CERT, among other security-related activities, regularly analyzes software vulnerability reports and assesses the risk to the Internet and other critical infrastructure. Robert is an adjunct professor in the Carnegie Mellon University School of Computer Science and in the Information Networking Institute and part-time faculty at the University of Pittsburgh. An eclectic technologist, Robert is author of three previous books, Secure Coding in C and C++ (Addison- Wesley, 2005), Building Systems from Commercial Components (Addison-Wesley, 2002), and Modernizing Legacy Systems (Addison-Wesley, 2003), as well as more than 40 papers on software security, componentbased software engineering, Web-based system design, legacy-system modernization, component repositories and search engines, and user interface design and development. Robert started programming professionally for IBM in 1982, working in communications and operating system software, processor development, and software engineering. Robert also has worked at the X Consortium, where he developed and maintained code for the Common Desktop Environment and the X Window System. He represents Carnegie Mellon at PL22. 11 (ANSI "C") and is a technical expert for the JTC1/SC22/WG14 international standardization working group for the C programming language.
Content
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
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