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Dynamic memory management is a common source of programming flaws that can lead to security vulnerabilities. Decisions regarding how dynamic memory is allocated, used, and deallocated are the burden of the programmer. Poor memory management can lead to security issues, such as heap-buffer overflows, dangling pointers, and double-free issues [Seacord 2005a2013]. From the programmer's perspective, memory management involves allocating memory, reading and writing to memory, and deallocating memory.

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To avoid these situations, memory should be allocated and freed at the same level of abstraction and, ideally, in the same code module. This includes the use of the following memory allocation and deallocation functions described in Section subclause 7.23.3 of the C Standard [ISO/IEC 9899:2011]:

void *malloc(size_t size);

void *calloc(size_t nmemb, size_t size);

void *realloc(void *ptr, size_t size);

void *aligned_alloc(size_t alignment, size_t size);
 
void free(void *ptr);

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enum { MIN_SIZE_ALLOWED = 32 };

int verify_size(char *list, size_t size) {
  if (size < MIN_SIZE_ALLOWED) {
    /* Handle Errorerror Conditioncondition */
    free(list);
    return -1;
  }
  return 0;
}

void process_list(size_t number) {
  char *list = (char *)malloc(number);
  if (list == NULL) {
    /* Handle Allocationallocation Errorerror */
  }

  if (verify_size(list, number) == -1) {
      free(list);
      return;
  }

  /* Continue Processingprocessing list */

  free(list);
}

The call to free memory in the verify_size() function takes place in a subroutine of the process_list() function, at a different level of abstraction from the allocation, resulting in a violation of this recommendation. The memory deallocation also occurs in error-handling code, which is frequently not as well tested as "green paths" through the code.

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enum { MIN_SIZE_ALLOWED = 32 };

int verify_size(const char *list, size_t size) {
  if (size < MIN_SIZE_ALLOWED) {
    /* Handle Errorerror Conditioncondition */
    return -1;
  }
  return 0;
}

void process_list(size_t number) {
  char *list = (char *)malloc(number);

  if (list == NULL) {
    /* Handle Allocationallocation Errorerror */
  }

  if (verify_size(list, number) == -1) {
      free(list);
      return;
  }

  /* Continue Processingprocessing list */

  free(list);
}

Risk Assessment

The mismanagement of memory can lead to freeing memory multiple times or writing to already freed memory. Both of these coding errors can result in an attacker executing arbitrary code with the permissions of the vulnerable process. Memory management errors can also lead to resource depletion and denial-of-service attacks.

Automated Detection

Related Vulnerabilities

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

Related

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Guidelines

Bibliography

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