125 lines
4.1 KiB
Markdown
125 lines
4.1 KiB
Markdown
## Piston
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Piston is the underlying engine for running untrusted and possibly malicious code that originates
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from from EMKC contests and challenges. It's also used in the Engineer Man Discord server via
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[felix bot](https://github.com/engineer-man/felix).
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#### Installation
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```
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# clone and enter repo
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git clone https://github.com/engineer-man/piston
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cd piston/lxc
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# install dependencies
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# centos:
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yum install -y epel-release
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yum install -y lxc lxc-templates debootstrap libvirt
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# everything else:
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# not documented, please open pull requests with commands for ubuntu/debian/arch/macos
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# start libvirtd
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systemctl start libvirtd
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# create and start container
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lxc-create -t download -n piston -- --dist ubuntu --release bionic --arch amd64
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./start
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# open a shell to the container
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./shell
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# install all necessary piston dependencies
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echo 'export PATH=/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin' >> /root/.bashrc
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echo 'export PATH=$PATH:/root/.cargo/bin' >> /root/.bashrc
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sed -i \
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's/http:\/\/archive.ubuntu.com\/ubuntu/http:\/\/mirror.math.princeton.edu\/pub\/ubuntu/' \
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/etc/apt/sources.list
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apt-get update
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apt-get -y install git tzdata nano \
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dpkg-dev build-essential python python3 \
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ruby nodejs golang php7.2 r-base mono-complete \
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nasm openjdk-8-jdk ubuntu-make bf
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umake swift
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ln -s /root/.local/share/umake/swift/swift-lang/usr/bin/swift /usr/bin/swift
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curl https://sh.rustup.rs -sSf | sh
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ln -s /root/.cargo/bin/rustc /usr/bin/rustc
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rm -rf /home/ubuntu
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chmod 777 /tmp
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chmod 777 -R /root
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# create runnable users and apply limits
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for i in {1..150}; do
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useradd -M runner$i
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usermod -d /tmp runner$i
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echo "runner$i soft nproc 64" >> /etc/security/limits.conf
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echo "runner$i hard nproc 64" >> /etc/security/limits.conf
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echo "runner$i soft nofile 2048" >> /etc/security/limits.conf
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echo "runner$i hard nofile 2048" >> /etc/security/limits.conf
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done
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# leave container
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exit
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# optionally run tests
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cd ../tests
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./test_all_lxc
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```
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#### CLI Usage
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- `lxc/execute [language] [file path] [arg]...`
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#### API Usage
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The Piston API exposes one endpoint at `http://127.0.0.1:2000/execute`.
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This endpoint takes the following JSON payload and expects at least the language and source. If
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source is not provided, a blank file is passed as the source.
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```json
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{
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"language": "js",
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"source": "console.log(process.argv)",
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"args": [
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"1",
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"2",
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"3"
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]
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}
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```
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A typical response when everything succeeds will be similar to the following:
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```json
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{
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"ran": true,
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"output": "[ '/usr/bin/node',\n '/tmp/code.code',\n '1',\n '2',\n '3' ]"
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}
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```
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If an invalid language is supplied, a typical response will look like the following:
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```json
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{
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"code": "unsupported_language",
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"message": "whatever is not supported by Piston"
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}
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```
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#### Supported Languages
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Currently python2, python3, c, c++, go, node, ruby, r, c#, nasm, php, java, swift, brainfuck, rust, and bash is supported.
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#### Principle of Operation
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Piston utilizes LXC as the primary mechanism for sandboxing. There is a small API written in Go which takes
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in execution requests and executes them in the container. High level, the API writes
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a temporary source and args file to `/tmp` and that gets mounted read-only along with the execution scripts into the container.
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The source file is either ran or compiled and ran (in the case of languages like c, c++, c#, go, etc.).
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#### Security
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LXC provides a great deal of security out of the box in that it's separate from the system.
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Piston takes additional steps to make it resistant to
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various privilege escalation, denial-of-service, and resource saturation threats. These steps include:
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- Disabling outgoing network interaction
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- Capping max processes at 64 (resists `:(){ :|: &}:;`, `while True: os.fork()`, etc.)
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- Capping max files at 2048 (resists various file based attacks)
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- Mounting all resources read-only (resists `sudo rm -rf --no-preserve-root /`)
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- Running as a variety of unprivileged users
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- Capping runtime execution at 3 seconds
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- Capping stdout to 65536 characters (resists yes/no bombs and runaway output)
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- SIGKILLing misbehaving code
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#### License
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Piston is licensed under the MIT license.
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