static void tun_set_sndbuf(struct tun_struct *tun)
{
	struct tun_file *tfile;
	int i;

	for (i = 0; i < tun->numqueues; i++) {
		tfile = rtnl_dereference(tun->tfiles[i]);
		tfile->socket.sk->sk_sndbuf = tun->sndbuf;
	}
}

The product dereferences a pointer that it expects to be valid but is NULL.