ebkalderon / bastille

Process sandboxing library written in Rust

Bastille

A process sandboxing library written in Rust.

Please note that this sandboxing library is a work in progress and has not yet been reviewed for correctness and overall security, so use at your own risk.

Motivation

At the time of writing, Arch Linux chose to enable unprivileged namespace support with kernel version +5.1.8, meaning that gaol now finally works on Arch Linux. However, it relies on a chroot jail which is rather easy to escape, and the API is also incompatible with std::command::Command. rusty-sandbox works as expected on macOS using more secure methods, but Linux is unsupported and it does not allow for filesystem mapping and mounting nor fine-grained access control.

Work in progress

• Spawn commands under a cloned process in a new namespace.
• Environment variables, arguments, and current working directory can be configured via the standard std::process::Command builder.
• Command stdio can be configured via the standard std::process::Command builder (this is currently unsupported until rust-lang/rust#44434 is resolved).
• Multiple sandboxes can be spawned in multi-threaded programs without interfering with each other (this is possible because clone(2) ensures process isolation between parent and sandbox).
• Sandbox spawned in one thread doesn't elevate user privileges for all other threads in the parent process, meaning other threads in Rust code aren't inadvertently granted Super Cow Powers (this is possible because setfsuid and capset are per-thread rather than per-process, and any times that Bastille does call setuid, we are in a separate child process).
• Unshare the user namespace (always on; will add the option to toggle off if requested, should Bastille detect the process is setuid).
• Unshare the network namespace (WIP, successfully unshares and creates a local loopback device, but the interface has some configuration issues).
• Unshare the PID namespace.
• Unshare the IPC namespace.
• Unshare the UTS (system hostname and NIS domain name) namespace.
• Set up filesystem sandbox:
  • Canonicalize all paths in mappings (eliminating symlinks), create a new tmpfs mount point for the new root in $base_path, create a dir $base_path/new_root, pivot_root() to $base_path, put the old root in $base_path/old_root. Next, set up new_root with all the mounts, directories, symlinks, etc. and pivot_root() again to /new_root, unmount /old_root, and unshare mount permissions.
• Add macOS backend using sandboxd (very heavy WIP).
• Add FreeBSD backend using capsicum (don't have a box to test with ATM).
• Add OpenBSD backend using pledge (don't have a box to test with ATM).

Credit

Design for the Linux backend implementation is loosely inspired by Bubblewrap.

License

Bastille is free and open source software distributed under the terms of the MIT and the Apache 2.0 licenses.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.