Thread: Overflow example and order of memory allocation

Small code to show overflow

But when I compile and run - buffer_one is not being overwritten when the byte size of buffer_two overflows - can someone please explain why?

Code:

#include <stdio.h>#include <string.h>

int main(int argc, char *argv[]) {
  int value = 5;
  char buffer_one[8], buffer_two[8];

  strcpy(buffer_two, "two");    //Put "one" into buffer_one
  strcpy(buffer_one, "one");    //Put "two" into buffer_two

  printf("[BEFORE] buffer_two is at %p and contains \'%s\'\n", buffer_two, buffer_two);
  printf("[BEFORE] buffer_one is at %p and contains \'%s\'\n", buffer_one, buffer_one);
  printf("[BEFORE] value is at %p and is %d (0x%08x)\n", &value, value, value);

  printf("\n[STRCPY] copying %zu bytes into buffer_two\n\n", strlen(argv[1]));
  strcpy(buffer_two, argv[1]);  //Copy first argument into buffer_two.

  printf("[AFTER] buffer_two is at %p and contains \'%s\'\n", buffer_two, buffer_two);
  printf("[AFTER] buffer_one is at %p and contains \'%s\'\n", buffer_one, buffer_one);
  printf("[AFTER] value is at %p and is %d (0x%08x)\n", &value, value, value);
}

user@ubuntu:~/examples$ ./overflow_example 1234567890
[BEFORE] buffer_two is at 0x7fff918ff210 and contains 'two'
[BEFORE] buffer_one is at 0x7fff918ff200 and contains 'one'
[BEFORE] value is at 0x7fff918ff1fc and is 5 (0x00000005)

[STRCPY] copying 10 bytes into buffer_two

[AFTER] buffer_two is at 0x7fff918ff210 and contains '1234567890'
[AFTER] buffer_one is at 0x7fff918ff200 and contains 'one'
[AFTER] value is at 0x7fff918ff1fc and is 5 (0x00000005)
*** stack smashing detected ***: ./overflow_example terminated
Aborted (core dumped)