ScreenRuster

An X11 screen saver and locker.

Installation

To install the daemon you will need a nightly toolchain, then you can use Cargo:

cargo install screenruster

Once that's done you can create a configuration file at $XDG_CONFIG_HOME/screenruster/config.toml ($XDG_CONFIG_HOME defaults to ~/.config/) or copy one from assets/config.toml.

Screen savers have to be in $PATH and the executable name has to start with screenruster-saver-.

A sample screen saver can be installed with Cargo:

cargo install screenruster-saver-laughing_man

The sample configuration file already has default settings for it.

Available savers

Tthis is a list of available screen savers that will be updated over time, if you made a saver and want it added here just open a pull request.

• Laughing Man from Ghost in the Shell: Stand Alone Complex

Architecture

The architecture loosely follows xscreensaver because it's the best approach, keep the screen locking simple and delegate the fancy graphics to a separate proccess, this has the nice property of making buggy savers not bring down the whole locking mechanism, thus protecting from vulnerabilities.

The savers can be written in any language that can draw to an X11 window, parse and generate JSON, write to stdout and read from stdin.

JSON is used for IPC between the daemon and the saver, the daemon writes to the saver process stdin, reads from the process stdout and forwards anything coming from stderr to allow for debugging or logging.

The job of the saver is merely to do the rendering, this includes any fade in/out or dialog boxes, this further reduces the attack surface of the locker. Note that the saver does not actually get the input, it just gets Insert or Delete events, so it can fill its dialog box.

Protocol

The protocol is line based, where each line contains a JSON encoded message, each message has a type field with the name of the message, the parameters are attributes on the same object.

Requests

Requests are messages sent from the daemon to the spawned saver process.

Configuration

The configuration request is part of the handshake and it's the first request sent when a process is spawned.

The configuration is monolithic and managed by the daemon in a TOML file, the related TOML map is converted to JSON and sent to the saver.

• type = config
• config = Object

Target

The target request is part of the handshake and is the second request sent when a process is spawned.

It contains the details required to get the X11 window, the display name, the screen number and the window XID.

• type = target
• display = String
• screen = Integer
• window = Integer

Resize

The resize request is sent when a locker window is resized, this can happen if XRandr is used to change resolution or rotate the screen.

• type = resize
• width = Integer
• height = Integer

Throttle

The throttle request is sent when the saver should try and reduce power usage.

• type = throttle
• throttle = Boolean

Blank

The blank request is sent when the screen has been blanked or unblanked.

• type = blank
• throttle = Boolean

Pointer

The pointer request is sent when a pointer event on the saver window has happened.

• type = pointer
• move = Object { x, y }
• buttonn = Object { x, y, button, press }

Password

The password request is sent when any authorization related changes happened, this includes when characters are being inserted or deleted, the password is being checked or authorization failed or succeded.

• type = password
• password = insert, delete, reset, check, success, failure

Start

The start request is sent when the saver should start its rendering, this may include a fade in or other fancy graphics.

• type = start

Stop

The stop request is sent when the saver should stop its rendering, this may include a fade out or other fancy graphics.

• type = stop

Responses

Responses are messages sent from the spawned saver process to the daemon.

Initialized

The initialized response is sent after the handshake is done and the saver is ready to start, since fancy graphics may require loading textures and such, the saver is given some leeway to get ready to render.

• type = initialized

Started

The started response is sent after a start request has been received and the saver started its rendering, it tells the daemon it can show the window.

• type = started

Stopped

The stopped response is sent after a stop request has been received and the saver stopped its rendering, it tells the daemon it can hide the window.

Authorization

There are various authorization modules.

Internal

The internal module uses a password specified in the configuration file.

[auth.internal]
password = "password"

PAM

The PAM module uses the Pluggable Authentication Module, you will need to install a configuration file for it in /etc/pam.d/screenruster.

auth	include		system-auth

If you want PAM account management to be respected, make sure to build with the auth-pam-accounts feature.