Safe allocation and deallocation of memory in C

The maximum number of locations kept track of can be modified by changing MAX_LOCin safe_mem.c

• hijacking
• direct usage

A shell script hijack.sh is provided.

Make sure to have the safe_mem.c file in the working directory.

Assuming the client file is hijack_client.c, run :

hijack.sh hijack_client

hijack.out is produced

• smalloc
• sfree

Sample client ( client.c )

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

int main() {
  char *ptr = smalloc(sizeof(char));
  int *arr = smalloc(5 * sizeof(int));

  // double free will not cause segmentation fault
  sfree(ptr);
  sfree(ptr);

  sfree(arr);

  int a = 5;
  int *b = &a;
  // freeing location on stack will not cause segmentation fault
  sfree(b);
}

gcc client.c safe_mem.c

Invalid free()!!, not freeing memory at location 0x557d7858d2a0
Invalid free()!!, not freeing memory at location 0x7fff397ff17c