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Memory Leak

Memory Leak

Description

A memory leak is an unintentional form of memory consumption whereby the application fails to free an allocated block of memory when no longer needed. The consequences of such an issue depend on the application itself.

Consider the following general three cases:

  • Short Lived User*land Application: Little if any noticeable effect. Modern operating system recollects lost memory
  • after program termination.
  • Long Lived User*land Application: Application Potentially dangerous. These applications continue to waste memory
  • over time, eventually consuming all RAM resources. Leads to abnormal system behavior.
  • Kernel*land Process: Very dangerous. Memory leaks in the kernel level lead to serious system stability issues. Kernel
  • memory is very limited compared to user land memory and should be handled cautiously.

The following example is basic memory leak in C:

#include <stdlib.h>
#include <stdio.h>

#define  LOOPS    10
#define  MAXSIZE  256

int main(int argc, char **argv)
{
     int count = 0;
     char *pointer = NULL;

     for(count=0; count<LOOPS; count++) {
          pointer = (char *)malloc(sizeof(char) * MAXSIZE);
     }

     free(pointer);

     return count;
}

In this example, we have 10 allocations of size MAXSIZE. Every allocation, except the last, is lost. If no pointer is pointed to the allocated block, it is unrecoverable during program execution. A simple fix to this trivial example is to place the free() call inside the ‘for’ loop.

Recommendation

Avoiding memory leaks in applications is difficult. There are tools with aide in tracking down such memory leaks like Valgrind or using modern compiler tools like ASAN, MSAN and UBSAN.

Valgrind runs the desired program in an environment such that all memory allocation and de-allocation routines are checked. At the end of program execution, Valgrind will display the results in an easy-to-read manner.

Categories

  • OWASP_MASVS_L1:
    • MSTG_CODE_8
  • OWASP_MASVS_L2:
    • MSTG_CODE_8