#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/syscall.h>

/*
  The House of Orange uses an overflow in the heap to corrupt the _IO_list_all pointer
  It requires a leak of the heap and the libc
  Credit: http://4ngelboy.blogspot.com/2016/10/hitcon-ctf-qual-2016-house-of-orange.html
*/

/*
   This function is just present to emulate the scenario where
   the address of the function system is known.
*/
int winner ( char *ptr);

int main()
{
    /*
      The House of Orange starts with the assumption that a buffer overflow exists on the heap
      using which the Top (also called the Wilderness) chunk can be corrupted.
      
      At the beginning of execution, the entire heap is part of the Top chunk.
      The first allocations are usually pieces of the Top chunk that are broken off to service the request.
      Thus, with every allocation, the Top chunks keeps getting smaller.
      And in a situation where the size of the Top chunk is smaller than the requested value,
      there are two possibilities:
       1) Extend the Top chunk
       2) Mmap a new page

      If the size requested is smaller than 0x21000, then the former is followed.
    */

    char *p1, *p2;
    size_t io_list_all, *top;

    fprintf(stderr, "The attack vector of this technique was removed by changing the behavior of malloc_printerr, "
        "which is no longer calling _IO_flush_all_lockp, in 91e7cf982d0104f0e71770f5ae8e3faf352dea9f (2.26).\n");
  
    fprintf(stderr, "Since glibc 2.24 _IO_FILE vtable are checked against a whitelist breaking this exploit,"
        "https://sourceware.org/git/?p=glibc.git;a=commit;h=db3476aff19b75c4fdefbe65fcd5f0a90588ba51\n");

    /*
      Firstly, lets allocate a chunk on the heap.
    */

    p1 = malloc(0x400-16);

    /*
       The heap is usually allocated with a top chunk of size 0x21000
       Since we've allocate a chunk of size 0x400 already,
       what's left is 0x20c00 with the PREV_INUSE bit set => 0x20c01.

       The heap boundaries are page aligned. Since the Top chunk is the last chunk on the heap,
       it must also be page aligned at the end.

       Also, if a chunk that is adjacent to the Top chunk is to be freed,
       then it gets merged with the Top chunk. So the PREV_INUSE bit of the Top chunk is always set.

       So that means that there are two conditions that must always be true.
        1) Top chunk + size has to be page aligned
        2) Top chunk's prev_inuse bit has to be set.

       We can satisfy both of these conditions if we set the size of the Top chunk to be 0xc00 | PREV_INUSE.
       What's left is 0x20c01

       Now, let's satisfy the conditions
       1) Top chunk + size has to be page aligned
       2) Top chunk's prev_inuse bit has to be set.
    */

    top = (size_t *) ( (char *) p1 + 0x400 - 16);
    top[1] = 0xc01;

    /* 
       Now we request a chunk of size larger than the size of the Top chunk.
       Malloc tries to service this request by extending the Top chunk
       This forces sysmalloc to be invoked.

       In the usual scenario, the heap looks like the following
          |------------|------------|------...----|
          |    chunk   |    chunk   | Top  ...    |
          |------------|------------|------...----|
      heap start                              heap end

       And the new area that gets allocated is contiguous to the old heap end.
       So the new size of the Top chunk is the sum of the old size and the newly allocated size.

       In order to keep track of this change in size, malloc uses a fencepost chunk,
       which is basically a temporary chunk.

       After the size of the Top chunk has been updated, this chunk gets freed.

       In our scenario however, the heap looks like
          |------------|------------|------..--|--...--|---------|
          |    chunk   |    chunk   | Top  ..  |  ...  | new Top |
          |------------|------------|------..--|--...--|---------|
     heap start                            heap end

       In this situation, the new Top will be starting from an address that is adjacent to the heap end.
       So the area between the second chunk and the heap end is unused.
       And the old Top chunk gets freed.
       Since the size of the Top chunk, when it is freed, is larger than the fastbin sizes,
       it gets added to list of unsorted bins.
       Now we request a chunk of size larger than the size of the top chunk.
       This forces sysmalloc to be invoked.
       And ultimately invokes _int_free

       Finally the heap looks like this:
          |------------|------------|------..--|--...--|---------|
          |    chunk   |    chunk   | free ..  |  ...  | new Top |
          |------------|------------|------..--|--...--|---------|
     heap start                                             new heap end



    */

    p2 = malloc(0x1000);
    /*
      Note that the above chunk will be allocated in a different page
      that gets mmapped. It will be placed after the old heap's end

      Now we are left with the old Top chunk that is freed and has been added into the list of unsorted bins


      Here starts phase two of the attack. We assume that we have an overflow into the old
      top chunk so we could overwrite the chunk's size.
      For the second phase we utilize this overflow again to overwrite the fd and bk pointer
      of this chunk in the unsorted bin list.
      There are two common ways to exploit the current state:
        - Get an allocation in an *arbitrary* location by setting the pointers accordingly (requires at least two allocations)
        - Use the unlinking of the chunk for an *where*-controlled write of the
          libc's main_arena unsorted-bin-list. (requires at least one allocation)

      The former attack is pretty straight forward to exploit, so we will only elaborate
      on a variant of the latter, developed by Angelboy in the blog post linked above.

      The attack is pretty stunning, as it exploits the abort call itself, which
      is triggered when the libc detects any bogus state of the heap.
      Whenever abort is triggered, it will flush all the file pointers by calling
      _IO_flush_all_lockp. Eventually, walking through the linked list in
      _IO_list_all and calling _IO_OVERFLOW on them.

      The idea is to overwrite the _IO_list_all pointer with a fake file pointer, whose
      _IO_OVERLOW points to system and whose first 8 bytes are set to '/bin/sh', so
      that calling _IO_OVERFLOW(fp, EOF) translates to system('/bin/sh').
      More about file-pointer exploitation can be found here:
      https://outflux.net/blog/archives/2011/12/22/abusing-the-file-structure/

      The address of the _IO_list_all can be calculated from the fd and bk of the free chunk, as they
      currently point to the libc's main_arena.
    */

    io_list_all = top[2] + 0x9a8;

    /*
      We plan to overwrite the fd and