copy_to_user undefined in linux kernel version 4.12.8

You should use #include <linux/uaccess.h> for 4.12.8. Here is the definition.

In 4.4 some drivers use #include <asm/uaccess.h> whilst the others use #include <linux/uaccess.h>.

#include <linux/uaccess.h> is preferable, I think.

You should do apt-get update and then apt-get install linux-headers-generic.