Piston

Piston is the underlying engine for running untrusted and possibly malicious code that originates from EMKC contests and challenges. It's also used in the Engineer Man Discord server via I Run Code bot as well as 1000+ other servers. To get it in your own server, go here: https://emkc.org/run.

Use Public API (new)

Requires no installation and you can use it immediately. Reference the API Usage section below to learn about the request format but rather than using the local URLs, use the following URLs:

• GET https://emkc.org/api/v1/piston/versions
• POST https://emkc.org/api/v1/piston/execute

Important Note: The Piston API is rate limited to 5 requests per second

Installation

Updated installation instructions coming soon. See var/install.txt for how to do it from scratch.

CLI Usage

• lxc/execute [language] [file path] [args]

API Usage

To use the API, it must first be started. To start the API, run the following:

cd api
./start

Base URLs

For your own local installation, use:

http://127.0.0.1:2000

When using the public Piston API, use:

https://emkc.org/api/v1/piston

Versions Endpoint

GET /versions This endpoint takes no input and returns a JSON array of the currently installed languages.

Truncated response sample:

HTTP/1.1 200 OK
Content-Type: application/json

[
    {
        "name": "awk",
        "version": "1.3.3"
    },
    {
        "name": "bash",
        "version": "4.4.20"
    },
    {
        "name": "c",
        "version": "7.5.0"
    }
]

Execution Endpoint

POST /execute This endpoint takes the following JSON payload and expects at least the language and source. If source is not provided, a blank file is passed as the source.

{
    "language": "js",
    "source": "console.log(process.argv)",
    "args": [
        "1",
        "2",
        "3"
    ]
}

A typical response when everything succeeds will be similar to the following:

HTTP/1.1 200 OK
Content-Type: application/json

{
    "ran": true,
    "language": "js",
    "version": "12.13.0",
    "output": "[ '/usr/bin/node',\n  '/tmp/code.code',\n  '1',\n  '2',\n  '3' ]"
}

If an invalid language is supplied, a typical response will look like the following:

HTTP/1.1 400 Bad Request
Content-Type: application/json

{
    "code": "unsupported_language",
    "message": "whatever is not supported by Piston"
}

Supported Languages

• awk
• bash
• c
• cpp
• csharp
• deno
• erlang
• elixir
• emacs
• go
• haskell
• java
• jelly
• julia
• kotlin
• nasm
• node
• perl
• php
• python2
• python3
• paradoc
• ruby
• rust
• swift
• typescript

Principle of Operation

Piston utilizes LXC as the primary mechanism for sandboxing. There is a small API written in Go which takes in execution requests and executes them in the container. High level, the API writes a temporary source and args file to /tmp and that gets mounted read-only along with the execution scripts into the container. The source file is either ran or compiled and ran (in the case of languages like c, c++, c#, go, etc.).

Security

LXC provides a great deal of security out of the box in that it's separate from the system. Piston takes additional steps to make it resistant to various privilege escalation, denial-of-service, and resource saturation threats. These steps include:

• Disabling outgoing network interaction
• Capping max processes at 64 (resists :(){ :|: &}:;, while True: os.fork(), etc.)
• Capping max files at 2048 (resists various file based attacks)
• Mounting all resources read-only (resists sudo rm -rf --no-preserve-root /)
• Cleaning up all temp space after each execution (resists out of drive space attacks)
• Running as a variety of unprivileged users
• Capping runtime execution at 3 seconds
• Capping stdout to 65536 characters (resists yes/no bombs and runaway output)
• SIGKILLing misbehaving code

License

Piston is licensed under the MIT license.