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Before the lifetime of the last pointer object that stores the return value of a call to a standard memory allocation function has ended, it must be matched by a call to a standard memory deallocation function free() with that pointer value.

Noncompliant Code Example

In this noncompliant example, the object allocated by the call to malloc() is not freed before the end of the lifetime of the last pointer object (text_buffer) referring to the object.:

#include <stdlib.h>
 
constenum size_t{ BUFFER_SIZE = 32 };

int f(void) {
  char *text_buffer = (char *)malloc(BUFFER_SIZE); 
  if (text_buffer == NULL) {
    return -1;
  }
  return 0;
}

Compliant Solution

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In this compliant solution, the pointer is deallocated with a call to free(). :

Code Block
bgColor #ccccff lang c
#include <stdlib.h> constenum size_t{ BUFFER_SIZE = 32 }; int f(void) { char *text_buffer = (char *)malloc(BUFFER_SIZE); if (text_buffer == NULL) { return -1; }   free(text_buffer); return 0; }

Exceptions

MEM31-C-EX1: Allocated memory does not need to be freed if it is used throughout the lifetime of the programassigned to a pointer whose lifetime includes program termination. The following code example illustrates a pointer object that stores the return value from malloc() that is stored in a static variable.:

#include <stdlib.h>
 
constenum size_t{ BUFFER_SIZE = 32 };

int f(void) {
  static char *text_buffer = NULL;
  if (text_buffer == NULL) {
    text_buffer = (char *)malloc(BUFFER_SIZE); 
    if (text_buffer == NULL) {
      return -1;
    }
  }
  return 0;
}

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Failing to free memory can result in the exhaustion of system memory resources, which can lead to a denial-of-service attack.

Automated Detection

Related Vulnerabilities

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

Related Guidelines

Key here (explains table format and definitions)

CERT-CWE Mapping Notes

Key here for mapping notes

CWE-404/CWE-459/CWE-771/CWE-772 and FIO42-C/MEM31-C

Intersection( FIO42-C, MEM31-C) = Ø

CWE-404 = CWE-459 = CWE-771 = CWE-772

CWE-404 = Union( FIO42-C, MEM31-C list) where list =

• Failure to free resources besides files or memory chunks, such as mutexes)

Bibliography

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