The Bible study laptop had working internet and a panel that said there
was no connection. Both were true, and one thing caused both.
Measured on the machine:
nmcli device status wlp2s0 wifi unmanaged
nmcli networking connectivity none while curl fetched fine
nmcli device wifi list nothing, with the radio enabled
/run/network/ifstate wlp2s0=wlp2s0
a second wpa_supplicant, -i wlp2s0, with no -c config file
dhcpcd holding the lease
/etc/network/interfaces 0600 root:root
Debian's installer had been given the Wi-Fi, so it wrote it into
/etc/network/interfaces and ifupdown brings it up. NetworkManager ships
with plugins=ifupdown and [ifupdown] managed=false, so an interface named
in that file is UNMANAGED — which is why the applet had nothing to report
and why scanning found nothing. An unmanaged device is not a radio
NetworkManager will scan with. rfkill was ruled out separately: the radio
is enabled.
managed=false stays; it is what keeps a tower's static Ethernet where an
administrator put it. Only a wireless interface is moved.
classroom-wifi grows --check, --adopt (with --dry-run) and --rollback.
--adopt builds a NetworkManager SYSTEM connection from the SSID and key
already in that root-only file, so the password never leaves the machine
and never reaches a human or a log; it lands in a 0600 root file with
psk-flags=0, the same shape 0.2.4 established, and the polkit rules
protecting it are untouched.
Deliberately NOT run by the upgrade. It moves a machine's only link
between managers and the machine it could strand is a laptop in a locked
room, so classroom-migrate only looks and prints what it found. An
administrator runs it over SSH while watching.
Two things this learned from testing the rollback rather than from
reading the code, and both are why the rollback is worth testing:
* ifdown was missing in the lab, subprocess raised FileNotFoundError,
and the exception escaped AFTER the stanza was commented out. No
rollback ran. Every hand-over command now goes through a runner that
tolerates a missing binary, and the whole hand-over is inside a guard
that restores the file on any failure at all.
* it now refuses to start when ifdown or ifup are absent, because
without them the hand-over would be a one-way door.
Success also requires the interface itself to be carrying the connection,
not merely that the machine is online — a machine with a second link
would otherwise report a failed migration as a success.
Verified in the lab against real NetworkManager with a real ifupdown
file: --check and --dry-run leave it byte-identical, a failed --adopt
rolls back byte-identically, and --rollback restores a half-migrated
machine byte-identically and exits 0. The one thing no lab can do is the
hand-over succeeding, which needs the laptop's radio.
Co-Authored-By: Claude Opus 5 <[email protected]>
These are shared computers in rooms full of people, and in a stock Plasma
desktop "use the network" and "read the network's password" are much
closer together than they look.
Measured on Debian 13 with NetworkManager 1.52 and Plasma 6.3:
* org.freedesktop.NetworkManager.settings.modify.own ships as "yes" for
an active session — no prompt, no administrator. It covers any
connection whose connection.permissions names that user, and a Wi-Fi
network added from the desktop is created exactly that way. So a
password a teacher types in is readable by the next person to sit
down.
* the applet offers "Show Network's QR Code" on every saved wireless
connection, and the QR code contains the pre-shared key.
* that action, and the "Configure…" beside it, are contextual actions in
ConnectionItem.qml and do NOT consult
authorizeControlModule("kcm_networkmanagement"). The Kiosk key gates
the toolbar button only. Hiding buttons was never going to be the
answer.
Every one of those paths ends at NetworkManager's GetSecrets, so that is
where this is answered. A polkit rule refuses settings.modify.own,
settings.modify.system, both wifi.share actions and the machine-wide
settings, for the classroom user by name.
Deliberately NOT refused: network-control, wifi.scan and the
enable/disable actions. None returns a secret, and they are what
connecting and seeing a network are made of. Automatic reconnection does
not go through polkit at all — NetworkManager does it as root — so nothing
here can stop the room coming back on the network after a reboot, which is
the property that matters most on a Sunday.
An administrator's account and root are untouched, and the override route
is the same one the sleep rule has.
classroom-wifi is the other half, and it is a requirement rather than a
convenience: it provisions the church Wi-Fi as a SYSTEM connection, with
no connection.permissions, psk-flags=0 and a 0600 root:root file. A
connection the machine owns is one nobody in the room can read. Verified
against real NetworkManager in the lab — the classroom account gets
"Permission denied" on the file, "--" from nmcli and "Insufficient
privileges" from GetSecrets, while autoconnect stays on.
There is deliberately no teacher-facing join dialog. Anything that lets
the room add a connection lets the room own it, and an owned connection is
a readable one; docs/networking.md says so rather than leaving it to be
rediscovered.
The rule is plain JavaScript, so the test evaluates it with polkit's
objects stubbed and asserts both halves: which actions come back NO, and
which are left alone. What it cannot test is the last mile — polkit
resolves a subject through logind and a container has no graphical seat
session, so every check there is denied for reasons unrelated to this
rule. That one is a physical check, and it is written down as one.
Co-Authored-By: Claude Opus 5 <[email protected]>
