SEI CERT C Coding Standard

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If both size_t and unsigned long long types are represented as a 64-bit unsigned value, the result of the multiplication operation may not be representable as an unsigned long long value. See guideline rule INT35-C. Evaluate integer expressions in a larger size before comparing or assigning to that size for more information on upcasting.

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In this compliant solution, the integer values passed as size arguments to memory allocation functions are of the correct size and have not been altered due to integer overflow or truncation. (See guidelines rules INT32-C. Ensure that operations on signed integers do not result in overflow and INT31-C. Ensure that integer conversions do not result in lost or misinterpreted data.)

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This example checks the value of num_blocks to make sure the subsequent multiplication operation cannot result in an integer overflow. The code also ensures that num_blocks is not equal to zero. (See guideline recommendation MEM04-C. Do not perform zero length allocations.)

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Code Block
bgColor#ccccff
size_t len;
char *str;
char buf[BUFF_SIZE];

/* ... */
if (len < BUFF_SIZE){
  memcpy(buf, str, len);
}
/* ... */

See guideline recommendation INT01-C. Use rsize_t or size_t for all integer values representing the size of an object for more information on representing the size of objects.

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This example also checks for unsigned integer overflow in compliance with guideline rule INT32-C. Ensure that operations on signed integers do not result in overflow.

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The code also ensures that len is not equal to zero. (See guideline recommendation MEM04-C. Do not perform zero length allocations.)

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Tool

Version

Checker

Description

Section

Fortify SCA

Section

V. 5.0

 

Section

can detect violations of this rule with CERT C Rule Pack, except those involving the sizeof operator

Section

Coverity Prevent

Include Page
c:Coverity_V
c:Coverity_V
Section

SIZECHECK

Section

finds memory allocations that are assigned to a pointer that reference objects larger than the allocated block

Section

Coverity Prevent

Include Page
c:Coverity_V
c:Coverity_V
Section

BAD_ALLOC_STRLEN

Section

can find the instances where string length is miscalculated (length calculated may be one less than intended) for memory allocation purposes. Coverity Prevent cannot discover all violations of this rule so further verification is necessary

Section

Compass/ROSE

 

 

Section

could check violations of this rule by examining the size expression to malloc() or memcpy() functions. Specifically, the size argument should be bounded by 0, SIZE_MAX, and, unless it is a variable of type size_t or rsize_t, it should be bounds-checked before the malloc() call. If the argument is of the expression a*b, then an appropriate check is:

Code Block
if (a < SIZE_MAX / b && a > 0) ...

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Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Related Guidelines

CERT C++ Secure Coding Standard: MEM35-CPP. Allocate sufficient memory for an object

Bibliography

unmigrated-wiki-markup

\[[Coverity 2007|AA. Bibliography#Coverity 07]\] \[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\] Section 7.20.3, "Memory Management Functions" \[[

ISO/IEC PDTR 24772|AA. Bibliography#ISO/IEC PDTR 24772]\] TR 24772 "XYB Buffer Overflow in Heap"

MITRE CWE: CWE-190, "Integer Overflow (Wrap or Wraparound)"

MITRE CWE: CWE-131, "Incorrect Calculation of Buffer Size"

Bibliography

Wiki Markup
\[[Coverity 2007|AA. Bibliography#Coverity 07]\]
\[[MITRE 2007|AA. Bibliography#MITRE 07]\] [CWE ID 190|http://cwe.mitre.org/data/definitions/190.html], "Integer Overflow (Wrap or Wraparound)," and [CWE ID 131|http://cwe.mitre.org/data/definitions/131.html], "Incorrect Calculation of Buffer Size"
\[[Seacord 2005|AA. Bibliography#Seacord 05]\] Chapter 4, "Dynamic Memory Management," and Chapter 5, "Integer Security"
\[[xorl 2009|AA. Bibliography#xorl 2009]\] ["CVE-2009-0587: Evolution Data Server Base64 Integer Overflows"|http://xorl.wordpress.com/2009/06/10/cve-2009-0587-evolution-data-server-base64-integer-overflows/]

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