CVE-2024-43378: calamares-nixos-extensions LUKS keyfile exposure regression on legacy BIOS systems

calamares-nixos-extensions provides Calamares branding and modules for NixOS, a distribution of GNU/Linux. Users who installed NixOS through the graphical installer who used manual disk partitioning to create a setup where the system was booted via legacy BIOS rather than UEFI; some disk partitions are encrypted; but the partitions containing either / or /boot are unencrypted; have their LUKS disk encryption key file in plain text either in /cryptokeyfile.bin, or in a CPIO archive attached to their NixOS initrd. nixos-install is not affected, nor are UEFI installations, nor was the default automatic partitioning configuration on legacy BIOS systems. The problem has been fixed in calamares-nixos-extensions 0.3.17, which was included in NixOS. The current installer images for the NixOS 24.05 and unstable (24.11) channels are unaffected. The fix reached 24.05 at 2024-08-13 20:06:59 UTC, and unstable at 2024-08-15 09:00:20 UTC. Installer images downloaded before those times may be vulnerable. The best solution for affected users is probably to back up their data and do a complete reinstallation. However, the mitigation procedure in GHSA-3rvf-24q2-24ww should work solely for the case where / is encrypted but /boot is not. If / is unencrypted, then the /cryptokeyfile.bin file will need to be deleted in addition to the remediation steps in the previous advisory. This issue is a partial regression of CVE-2023-36476 / GHSA-3rvf-24q2-24ww, which was more severe as it applied to the default configuration on BIOS systems.