sudo-rs

A safety oriented and memory safe implementation of sudo and su written in Rust.

Status of this project

Sudo-rs is being developed further; features you might expect form original sudo may still be unimplemented or not planned. If there is an important one you need, please request it using the issue tracker. If you encounter any usability bugs, also please report them on the issue tracker. Suspected vulnerabilities can be reported on our security page.

An audit of sudo-rs will take place in September 2023, the next stable release will incorporate its results.

Sudo-rs currently is targeted for Linux-based operating systems only; Linux kernel 5.9 or newer is necessary to run sudo-rs.

Building it yourself

Sudo-rs is written in Rust. The minimum required Rust version is 1.70. If your Linux distribution does not package that version (or a later one), you can always install the most recent version through rustup. You also need the C development files for PAM (libpam0g-dev on Debian, pam-devel on Fedora).

With dependencies installed, building sudo-rs is a simple matter of:

cargo build --release

This produces a binary target/release/sudo. However, this binary must have the setuid flag set and must be owned by the root user in order to provide any useful functionality. Consult your operating system manual for details.

Sudo-rs needs the sudoers configuration file. The sudoers configuration file will be loaded from /etc/sudoers-rs if that file exists, otherwise the original /etc/sudoers location will be used. You must make sure that a valid sudoers configuration exists at that location. For an explanation of the sudoers syntax you can look at the original sudo man page.

Differences from original sudo

sudo-rs supports less functionality than sudo. Some of this is by design. In most cases you will get a clear error if you try something that is not supported (e.g. use a configuration flag or command line option that is not implemented).

Exceptions to the above, with respect to your /etc/sudoers configuration:

• use_pty is enabled by default, but can be disabled.
• env_reset is ignored --- this is always enabled.
• visiblepw is ignored --- this is always disabled.
• verifypw is currently ignored; a password is always necessary for sudo -v.
• mail_badpass, always_set_home, always_query_group_plugin and match_group_by_gid are not applicable to our implementation, but ignored for compatibility reasons.

Some other notable restrictions to be aware of:

• Some functionality is not yet supported; in particular sudoedit and preventing shell escapes using NOEXEC and NOINTERCEPT.
• Per-user, per-command, per-host Defaults sudoers entries for finer-grained control are not (yet) supported.
• Sudo-rs always uses PAM for authentication at this time, your system must be set up for PAM. Sudo-rs will use the sudo service configuration. This also means that resource limits, umasks, etc have to be configured via PAM and not through the sudoers file.
• sudo-rs will not include the sendmail support of original sudo.
• The sudoers file must be valid UTF-8.
• To prevent a common configuration mistake in the sudoers file, wildcards are not supported in argument positions for a command. E.g., %sudoers ALL = /sbin/fsck* will allow sudo fsck and sudo fsck_exfat as expected, but %sudoers ALL = /bin/rm *.txt will not allow an operator to run sudo rm README.txt, nor sudo rm -rf /home .txt, as with original sudo.

If you find a common use case for original sudo missing, please create a feature request for it in our issue tracker.

Aim of the project

Our current target is to build a drop-in replacement for all common use cases of sudo. For the sudoers config syntax this means that we support the default configuration files of common Linux distributions. Our implementation should support all commonly used command line options from the original sudo implementation.

Some parts of the original sudo are explicitly not in scope. Sudo has a large and rich history and some of the features available in the original sudo implementation are largely unused or only available for legacy platforms. In order to determine which features make it we both consider whether the feature is relevant for modern systems, and whether it will receive at very least decent usage. Finally, of course, a feature should not compromise the safety of the whole program.

Our su implementation is made using the building blocks we created for our sudo implementation. It will be suitable replacement for the su distributed by util-linux.

Future work

While our initial target is a drop-in replacement for most basic use cases of sudo, our work may evolve beyond that target. We are also looking into alternative ways to configure sudo without the sudoers config file syntax and to extract parts of our work in usable crates for other people.

Sponsors

The development of sudo-rs is an initiative of the Prossimo project by ISRG. An independent security audit of sudo-rs was made possible by the NLNet Foundation.