NixOS copies mode-carrying /etc entries such as authorized_keys.d during
stage-2 activation, which runs before systemd starts. preservation mounted the
persisted /etc/ssh from preservation.target afterwards and hid that copy, so a
key change only took effect on `switch`: revoking a key and rebooting silently
restored the old one.
Prepare the mount in initrd, before activation runs, and cover it with a VM
test that seeds a stale authorized_keys file, reboots, and asserts the declared
key replaced it. The same test fails on that assertion with inInitrd disabled.
Verified on all four hosts: /persistent/etc/ssh/authorized_keys.d/root is now
rewritten at boot instead of keeping the timestamp of the last switch.
Assisted-by: Claude Code (claude-opus-5-5)
The homelab hosts accept root SSH with long-lived file keys, run several
exposed services with almost no systemd sandboxing, and keep no audit trail of
privileged actions. Close those three gaps, weighing each measure against its
cost instead of adopting a policy wholesale.
SSH
- Turn off KbdInteractiveAuthentication: nixpkgs defaults it to true and PAM
then still accepts the Unix password despite PasswordAuthentication = false.
- authorizedKeysInHomedir = false: only keys declared in Nix take effect;
youko keeps Gitea's forced-command file through `Match User gitea`.
- Pin aquamarine's passphrase-free remote-builder keys to
`restrict,command="nix-daemon --stdio --store daemon"`, so builds run in the
system daemon instead of an audited root login session.
systemd sandboxing
- Add the mylib.systemdHardening preset and apply it to the exposed, weakly
sandboxed services: caddy 7.8 -> 1.5, vmalert 8.2 -> 1.4, rustfs 6.6 -> 1.4,
whisper-asr 7.7 -> 1.6. An eval test pins the key restrictions.
- Rejected: a global all-keys policy (<=0.2 score gains on services nixpkgs
already sandboxes) and per-service confinement (bind paths to maintain).
auditd on all four hosts, reusing nixpkgs' loader and unit
- Audit login sessions only: a first `-a never,task -F auid=unset` rule keeps
services out of the per-syscall audit path. A compromised service is
therefore unrecorded until it opens a session.
- Record root commands, credential and host-key access, writes to SSH, account,
PAM, Nix-trust and audit configuration, module loads and session denials.
- Rejected: global denial logging, service-UID watches and
--loginuid-immutable (the kernel already records loginuid changes).
Verified on all four hosts after deployment: zero failed units, k3s 6/6 Ready,
and the exposed services healthy.
Assisted-by: Claude Code (claude-opus-5-5)
* fix(nfs): restrict the golden export to its real clients
* fix(libvirt): bind VNC consoles to loopback
* fix(firewall): drop VNC ports on every host
* docs(security): record the NFS and VNC boundaries
Ryan Yin
ryan4yin | 二花