For #29793
# Details
This PR changes the way that Orbit launches processes such as the
desktop app on Linux, in order to ensure that on SELinux-enabled systems
the correct user context is set when running the command.
Previously, `sudo -u` was used to launch commands on Linux. This PR
switches to use `runuser` instead, which is recommended in situations
where the root user wants to execute a command as a user with reduced
privileges (see [the blog post by one of the creators of
runuser](https://danwalsh.livejournal.com/55588.html)). This avoids
certain errors that can come from interacting with PAM modules as the
system user.
Additionally, if we detect that SELinux is set up on a system, we now
use `runcon` to force the command to run using the logged-in user's
SELinux context. It's possible that on some systems they may have
configuration where `sudo` will switch to the user's SELinux context
automatically, but this is not guaranteed. Using `runuser` + `runcon` is
our best bet for ensuring that the desktop app (and anything that it
spawns) runs under the correct context.
This PR also does some refactoring so that the three `run` methods for
Linux (`run`, `runWithOutput` and `runWithStdin`) all use the same base
code to create the command with the correct args and env vars, and
differ only in how they handle the i/o.
# Checklist for submitter
If some of the following don't apply, delete the relevant line.
<!-- Note that API documentation changes are now addressed by the
product design team. -->
- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/guides/committing-changes.md#changes-files)
for more information.
- For Orbit and Fleet Desktop changes:
- [x] Make sure fleetd is compatible with the latest released version of
Fleet (see [Must
rule](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/workflows/fleetd-development-and-release-strategy.md)).
- [x] Orbit runs on macOS, Linux and Windows. Check if the orbit
feature/bugfix should only apply to one platform (`runtime.GOOS`).
- [x] ~Manual QA must be performed in the three main OSs, macOS, Windows
and Linux.~ (n/a, code is linux only)
- [x] ~Auto-update manual QA, from released version of component to new
version (see [tools/tuf/test](../tools/tuf/test/README.md)).~ n/a
# Testing
- [x] Ubuntu with SELinux on
- [x] Ubuntu with SELinux off
- [ ] Fedora with SELinux on
- [ ] Fedora with SELinux off
- [ ] Debian with SELinux on
- [x] Debian with SELinux off
- [x] `runWithOutput` still works (tested with `go run
./tools/dialog/main.go --dialog=zenity`)
- [ ] ~`runWithStdin` still works~ (this isn't currently used by Linux)
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Bug Fixes**
* Improved security and user context handling when launching the fleet
desktop application on Linux systems.
* **Refactor**
* Enhanced process launch mechanism to use proper SELinux context and
user session, ensuring processes start under the correct user and
security environment.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
