CertC-MEM31

Free dynamically allocated memory when no longer needed

Required inputs: IR, StaticSemanticAnalysis

Before the lifetime of the last pointer that stores the return value of a call to a standard memory allocation function has ended, it must be matched by a call to 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 text_buffer referring to the object:

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

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

Compliant Solution

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

#include <stdlib.h>

enum { 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 assigned to a pointer whose lifetime includes program termination. The following code example illustrates a pointer that stores the return value from malloc() in a static variable:

#include <stdlib.h>

enum { 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;
}

Risk Assessment

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

Rule	Severity	Likelihood	Remediation Cost	Priority	Level
MEM31-C	Medium	Probable	Medium	P8	L2

Related Guidelines

Taxonomy	Taxonomy item	Relationship
ISO/IEC TR 24772:2013	Memory Leak [XYL]	Prior to 2018-01-12: CERT: Unspecified Relationship
ISO/IEC TS 17961	Failing to close files or free dynamic memory when they are no longer needed [fileclose]	Prior to 2018-01-12: CERT: Unspecified Relationship
CWE 2.11	CWE-401, Improper Release of Memory Before Removing Last Reference ("Memory Leak")	2017-07-05: CERT: Exact
CWE 2.11	CWE-404	2017-07-06: CERT: Rule subset of CWE
CWE 2.11	CWE-459	2017-07-06: CERT: Rule subset of CWE
CWE 2.11	CWE-771	2017-07-06: CERT: Rule subset of CWE
CWE 2.11	CWE-772	2017-07-06: CERT: Rule subset of CWE

Bibliography

[ ISO/IEC 9899:2011]

Subclause 7.22.3, "Memory Management Functions"

Excerpt from SEI CERT C Coding Standard: Rules for Developing Safe, Reliable, and Secure Systems (2016 Edition) and SEI CERT C Coding Standard [https://cmu-sei.github.io/secure-coding-standards/sei-cert-c-coding-standard/rules/memory-management-mem/mem31-c], Copyright (C) 1995-2026 Carnegie Mellon University. See section 9.4. "3rd-Party Licenses" in the documentation for full details.

Possible Messages

Key	Text	Severity	Disabled
memory_leak	Call allocates leaking memory	None	False
possible_memory_leak	Call allocates possibly leaking memory	None	False

Options

• This rule shares the following common options: exclude_in_macros, exclude_messages_in_system_headers, excludes, extend_exclude_to_macro_invocations, includes, justification_checker, languages, post_processing, provider, report_at, severity

• The following places define options that affect this rule: Stylechecks, Analysis-GlobalOptions

resources

resources

Type: set[str]

Default: {'C++HeapMemory', 'CudaAsyncMemory', 'CudaDeviceMemory', 'CudaDriverAsyncMemory', 'CudaHostMemory', 'CudaManagedMemory', 'HeapMemory', 'UniquePtrHeapMemory'}

Set of resources to be checked (selection of rules in the Resources group).

 

witness_paths

witness_paths : bool = True

Whether witness paths should be determined and included in the issue.

 

witness_should_include_exception_handling

witness_should_include_exception_handling : bool = False

Whether to only accept witness paths that include some kind of exception handling.