About nullpo-mod

Nullpo-mod is a linux kernel module that implements a character device file that causes SEGV when it is about be either read or written.

Install

Build the kernel module.
```
$ make
```
Load the built module.
```
$ sudo insmod nullpo.ko
```

Usage

Reading more than or equal to 1 byte from /dev/nullpo will cause segmentation fault.

$ cat /den/nullpo
Segmentation fault (core dumped)

Writing more than or equal to 1 byte to /dev/nullpo will also cause segmentation fault.

$ echo foo | tee /dev/nullpo
Segmentation fault (core dumped)

read()/write() call for /dev/nullpo with 0 bytes reading/writing will be success with return value zero.

$ echo -n | tee /dev/nullpo
$ echo $?
0

Warning: redirecing to/from /dev/nullpo may cause a shell crash.

Supplement

To install the module to the system

You can install the module to the system and load from there.

$ sudo make install
$ sudo depmod
$ modprobe nullpo

I cannot open /dev/nullpo due to permission error

Depending to the system settings, /dev/nullpo cannot be opend except by root user. To grant permission for other user to open the device file, you have to create appropriate udev rules. There is a sample udev configuration file 99-nullpo.rules in the source directory. Putting that file into /etc/udev/rules.d grant permission for all users to read/write /dev/nullpo from next module loading.