feat: the room may use the church Wi-Fi and may not read its password

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]>

tools/build-release.sh

@@ -128,6 +128,12 @@ install -Dm755 \
     "$ROOT/scripts/classroom-printer-setup" \
     "$STAGE/usr/local/bin/classroom-printer-setup"
 
+# An administrator's command. The church Wi-Fi has to be provisioned as a
+# system connection or the classroom account can read its password.
+install -Dm755 \
+    "$ROOT/scripts/classroom-wifi" \
+    "$STAGE/usr/local/bin/classroom-wifi"
+
 # Shared helpers imported by the classroom commands.
 install -Dm644 \
     "$ROOT/lib/classroom_config.py" \
@@ -411,6 +417,12 @@ install -Dm644 \
     "$ROOT/config/polkit/org.ekklesia.classroom.sleep.rules" \
     "$STAGE/usr/share/polkit-1/rules.d/49-ekklesia-classroom-sleep.rules"
 
+# The classroom user cannot be shown a saved Wi-Fi password. Same place
+# and the same override route as the sleep rule above.
+install -Dm644 \
+    "$ROOT/config/polkit/org.ekklesia.classroom.network.rules" \
+    "$STAGE/usr/share/polkit-1/rules.d/49-ekklesia-classroom-network.rules"
+
 install -Dm644 \
     "$ROOT/config/plasma/autostart/ekklesia-classroom-scale.desktop" \
     "$STAGE/etc/xdg/autostart/ekklesia-classroom-scale.desktop"

tools/validate-trixie-release.sh

@@ -118,6 +118,20 @@ grep -q 'pipewire-pulse' "$audio_unit"
 command -v classroom-audio >/dev/null
 command -v pactl >/dev/null
 
+# The classroom account cannot be shown a saved Wi-Fi password. The rule
+# has to be installed, owned by root — polkit silently ignores a rules
+# file that is not — and it has to refuse the action Debian ships as
+# "yes", which is the one a teacher would actually reach.
+network_rules=/usr/share/polkit-1/rules.d/49-ekklesia-classroom-network.rules
+[[ -f "$network_rules" ]]
+[[ "$(stat -c %U:%G "$network_rules")" == "root:root" ]]
+grep -q "settings.modify.own" "$network_rules"
+grep -q "wifi.share.protected" "$network_rules"
+# And it must NOT refuse the actions that keep the room on the network.
+! grep -qE '"org\.freedesktop\.NetworkManager\.network-control"' "$network_rules"
+grep -q "kcm_networkmanagement=false" /etc/ekklesia-classroom/xdg/kdeglobals
+command -v classroom-wifi >/dev/null
+
 # The policy module and the daemon agree on what they import, on a machine
 # rather than in a checkout.
 PYTHONPATH=/usr/local/lib/ekklesia-classroom python3 -c \