Jorijn van der Graaf
928fe1482e
The trustlet has always reported WHICH finger matched and the daemon only ever used it to answer yes. A table in /etc/fingerprintd/actions.conf now gives each finger a meaning: run a command as root, tell the user's session, or report no-match while doing one of those anyway -- which is duress, where the phone should look like it simply did not recognise the finger. Two rules shaped the design. Root does not launch applications. The daemon has no session bus, no display and no user environment, so a `session` rule carries no command at all: the daemon emits net.catcrafts.Fingerprintd1.FingerMatched(finger, uid) and an agent in the user's own session decides what that means from the user's own configuration. The only commands in the file are ones root is meant to run. Which makes the file a root shell, and the parser treats it as one. It is refused outright unless root owns it and nobody else can write it, group included. A malformed line rejects the WHOLE file rather than being skipped: applying the prefix would leave a policy nobody wrote, and the missing half could be the one that mattered. That property is tested, and the test caught it being false the first time -- rules accumulated before the bad line survived the rejection. A system command must be an absolute path, because resolving a bare name through PATH makes what root runs depend on an environment this daemon does not control. It is double-forked with a scrubbed environment so an action may outlive the daemon (a reboot) without ever stalling the worker thread that is the only thread allowed to touch the trustlet. Ordering is deliberate: the verdict override happens before the client is told, because that is the point of duress; the session signal and the root command happen after, on the same principle that keeps the harvest and the save off the unlock path. No actions.conf ships. An example goes to /usr/share/doc, because shipping a root shell nobody asked for is not a default. Not yet exercised on hardware.
29 lines
1.5 KiB
XML
29 lines
1.5 KiB
XML
<?xml version="1.0" encoding="UTF-8"?> <!--*-nxml-*-->
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<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
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"http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
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<!-- SPDX-License-Identifier: GPL-3.0-only
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SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
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fingerprintd owns fprintd's bus name so pam_fprintd, the Plasma KCM and
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fprintd-enroll work unmodified. Same shape as fprintd's own policy: root
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owns the name, anyone may call it, and the daemon enforces who may act on
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whose prints.
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Install: /usr/share/dbus-1/system.d/net.reactivated.Fprint.conf -->
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<busconfig>
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<policy user="root">
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<allow own="net.reactivated.Fprint"/>
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<allow send_destination="net.reactivated.Fprint"/>
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</policy>
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<policy context="default">
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<allow send_destination="net.reactivated.Fprint"/>
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<allow receive_sender="net.reactivated.Fprint"/>
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</policy>
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<!-- net.catcrafts.Fingerprintd1.FingerMatched is ours, not fprintd's: it
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names the finger that just matched so an agent in the user's session
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can act on it. It is carried by the receive_sender rule above, which
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means any local user can see which finger the owner used and when.
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That is a real if small leak, and it is the price of letting an
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unprivileged session agent hear it at all, since D-Bus cannot address
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a signal to one uid. Acceptable on a single-user phone; a multi-user
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system should narrow the rule above to the intended uid. -->
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</busconfig>
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