Harden CUPS printer discovery

Run cups-browsed as a locked service account with a dedicated cache and a focused systemd sandbox. Restrict automatic queues to driverless IPP printers, remove wheel from passwordless CUPS administration, replace cups-pdf with Polkit-backed setup, and migrate existing systems safely.

Reported-By: Erik Hunstad (Bad Sector Labs)

Co-Authored-By: Daybreak Blue <noreply@openai.com>

etc/cups/cups-browsed.conf

@@ -1,4 +1,8 @@
-# Omarchy override of cups-browsed's shipped config. The only behavioural
-# change vs the upstream default (all-commented) is enabling auto-registration
-# of remote IPP printers discovered via Avahi/mDNS.
-CreateRemotePrinters Yes
+# Keep state away from /var/cache/cups, which is writable by the account CUPS
+# uses for print filters. cups-browsed is the only writer to this directory.
+CacheDir /var/cache/cups-browsed
+
+# Auto-create queues only for modern driverless IPP printers. Remote queues
+# exported by another CUPS server can still be added manually when needed.
+CreateIPPPrinterQueues Driverless
+CreateRemoteCUPSPrinterQueues No

etc/systemd/system/cups-browsed.service.d/10-omarchy.conf

@@ -0,0 +1,11 @@
+[Service]
+User=cups-browsed
+Group=cups-browsed
+CacheDirectory=cups-browsed
+CacheDirectoryMode=0750
+UMask=0027
+NoNewPrivileges=yes
+ProtectSystem=strict
+ProtectHome=yes
+PrivateTmp=yes
+RestrictSUIDSGID=yes

etc/sysusers.d/omarchy-cups-browsed.conf

@@ -0,0 +1 @@
+u cups-browsed - "CUPS printer discovery" / -