oki

oki

oki applies pledge(2) and unveil(2) restrictions to target-program, reducing the blast radius of a security vulnerability in target-program.

Synopsis

oki -R target-program
oki -p <promise> [options] target-program [target-program-options]
oki -k [options] target-program [target-program-options]

How does this work?

Calling pledge on a program restricts the set of allowed system calls. Each set of permitted system calls is known as a promise which can be combined. These promise strings are documented in man 2 pledge. If a program executes a system call that is not permitted by the promises, the kernel immediately terminates the program, delivering a core file if possible.

oki applies pledge restrictions using pledge's execpromises argument. This allows oki to apply pledge only to a newly executed process and not the current process. The user specifies promises using -p promise.

Calling unveil on a program removes visibility of the entire filesystem, expect for the specified path and permissions. Additional calls can set permissions at other points in the filesystem hierarchy. When applied to a directory, the permissions will apply to any file in the subtree of that directory.

oki unveils paths by calling unveil for each -u permission:path specified by the user. When oki executes the target-program, unveil restrictions are automatically inherited by the target-program. By default, oki automatically unveils the target-program executable specified by the user.

Features

• Applies specified promise strings to the pledge(2) system call on the target-program.
• Applies specified filepath and permissions to the unveil(2) system call on the target-program.
• Filters only HOME and PATH environment variables to the target-program.
• Optionally pass specific environment variables to the target-program.
• Autogenerate unveil rules for the imported libraries of the target-program and write the rules to standard out. This helps with writing scripts that call oki on the target-program.

Requirements

• An OpenBSD system (the application can be compiled on any OS, but it relies on tools included with OpenBSD)
• Go (Golang)

Installation

The preferred method of installation is using go install (as this is a Golang application). This automates downloading and building Go applications from source in a secure manner. By default, applications are copied into ~/go/bin/.

You must first install Go. If you are compiling the application on OpenBSD, you can install Go by executing:

doas pkg_add go

After installing Go, run the following commands to install the application:

go install github.com/SeungKang/oki@latest
doas cp ~/go/bin/oki /usr/local/bin/

Examples

The following example generates unveil rules for rizin's libraries:

$ oki -R /usr/local/bin/rizin
-u 'r:/usr/local/lib/librz_util.so.0.7' \
-u 'r:/usr/lib/libm.so.10.1' \
-u 'r:/usr/lib/libutil.so.16.0' \
(...)

The following example runs oki on the git program:

$ oki -p "stdio" -p "inet" -p + "error" -u "r:/tmp" -u "rc:/foo" -- git

The above example enforces the pledge(2) promises: "stdio", "inet", and "error". It also runs unveil(2) on the following paths:

• /tmp for read r operations
• /foo for read r and create/remove c operations

Troubleshooting

The -d option enables debug mode, which will log the pledge promise strings, unveil rules, and environment variables applied to the target-program. Pledge violations are logged in /var/log/messages.

Special Thanks

A mega thank you to Stephan Fox, he's the best :). Stephan played a significant role in assisting me with this project and discussions on its functionality. I'm eternally grateful for his support, encouragement, patience, and guidance through this project. Can't wait to do more.