Add an motd warning when ublue's keys are not enrolled

[castrojo]

We need to run this for a while in the MOTD and do a corresponding announcement on the forums. Let's block bringing fsync to stable. It'd help avoid situations like this: #1636

WARNING: This machine has secure boot turned on but you haven't enrolled Universal Blue's keys, follow <link>

[jardon]

So there would need to be a script that does the following pseudo code:

if secure_boot_enabled && key_not_imported
-> output message to terminal
- -> write file

I'm new here so I don't know all the constraints with the ublue stack, but I'm assuming writing to /etc/motd or /etc/motd.d/ is not possible. If not, maybe there's a solution with editing the user's .bashrc

I'm just spitballin`

[KyleGospo]

@jardon For development you can do sudo rpm-ostree usroverlay so you can edit your local file.

There's an existing check for the image being out of date that throws a "check engine light", that can be found here:
https://github.com/ublue-os/bluefin/blob/main/system_files/shared/usr/libexec/ublue-motd#L22

I would add another check like this and make the existing one an elif, use mokutil --list-enrolled to test for the key.

[hanthor]

The script's "good" state is reported to systemd as a failure:

systemctl status check-sb-key.service 
× check-sb-key.service - Service to check for secure boot key enrollment
     Loaded: loaded (/usr/lib/systemd/system/check-sb-key.service; enabled; preset: disabled)
    Drop-In: /usr/lib/systemd/system/service.d
             └─10-timeout-abort.conf
     Active: failed (Result: exit-code) since Fri 2024-10-25 16:56:40 IST; 4h 57min ago
   Duration: 87ms
 Invocation: 7f68ae1f16c44fc9868af9e9e32ebe92
    Process: 1594 ExecStart=/usr/libexec/check-sb-key.sh (code=exited, status=1/FAILURE)
   Main PID: 1594 (code=exited, status=1/FAILURE)
   Mem peak: 2.1M
        CPU: 14ms

Oct 25 16:56:40  systemd[1]: Started check-sb-key.service - Service to check for secure boot key enrollment.
Oct 25 16:56:40  check-sb-key.sh[1617]: /etc/pki/akmods/certs/akmods-ublue.der is already enrolled
Oct 25 16:56:40  systemd[1]: check-sb-key.service: Main process exited, code=exited, status=1/FAILURE
Oct 25 16:56:40  systemd[1]: check-sb-key.service: Failed with result 'exit-code'.