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standby unlock: a locked session unlocks by finger without PAM

Phosh's lock screen cannot take a fingerprint: its PAM conversation
answers every prompt with the password. So the daemon follows the seat
session that is locked and in front (logind LockedHint + Active), runs a
verify of its own while the display is on (backlight bl_power), and
answers a match with logind's Session.Unlock.

Only fingers named in that session owner's map unlock. The map is
re-read at every arm and verdict, and a delete cancels a running standby
verify, so a finger deleted while locked stops counting at once. A
verdict from an earlier lock or another session is dropped. no-unlock
rules and FingerMatched apply as for a client match. A client Claim
cancels standby, and its Release, or a claim that fails while pending,
re-arms it. --standby-unlock=off disables it.

Tested on the dev phone before the review fixes (map re-read,
front-session tracking, cancel ordering, pending-claim re-arm): under
Phosh, six unlocks by two fingers and an unnamed template refused; under
Plasma, kscreenlocker's pam_fprintd unlocks while standby yields and
re-arms. With the fixes: suites 8/8, and a daemon restart under a lock
screen picks the locked session up. Not exercised: standby's own
Session.Unlock on kscreenlocker, user switching.

2026-09-23 17:53:11 +02:00

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fingerprintd

Fingerprint daemon for the Fairphone 6 (milos, SM7635) on mainline Linux.

fingerprintd-core is a static library with no GLib, no libqcomtee and no system headers. Everything in it is a wire format or a state machine that was recovered by reverse-engineering, so all of it is pinned by tests that run on a dev box with no phone, no TEE and no sensor. The daemon shell holds everything that touches hardware.

Build

crafter-build              # bin/fingerprintd-<target>-<march>/fingerprintd
crafter-build test         # the unit suites

Cross-compiling for the phone:

packaging/make-sysroot.sh
crafter-build -- --target=aarch64-alpine-linux-musl --sysroot=~/.cache/fingerprintd/sysroot-aarch64-alpine --march=armv8.6-a+fp16fml+aes+sha3+sm4 --mtune=cortex-a720
crafter-build test --target=aarch64-alpine-linux-musl --sysroot=~/.cache/fingerprintd/sysroot-aarch64-alpine --march=armv8.6-a+fp16fml+aes+sha3+sm4 --mtune=cortex-a720

Verified on the device: all five suites pass cross-built and run on the phone itself, not only under emulation.

fprintd-enroll -f right-index-finger user   ten stages, enroll-completed
fprintd-list user                            - #0: right-index-finger
fprintd-verify user   (wrong finger)         verify-no-match, on the first press
fprintd-verify user   (enrolled finger)      verify-match,    on the first press

Lock-screen unlock

Two routes, both on by default:

PAM. The daemon provides fprintd, so a lock screen that runs pam_fprintd beside its password prompt unlocks by finger the usual way. Plasma's does (kde-fingerprint; the fingerprint-auth and postlogin services it needs are shipped here). Phosh's cannot: its PAM conversation answers every prompt with the password, so a fingerprint module in its stack would only stall the password behind the fingerprint timeout.
Standby. While the session in front on its seat is locked and the display is on, the daemon runs a verify of its own and answers a match with logind's Session.Unlock, which Phosh honours. No verify runs while the display is off (an open verify polls the sensor at ~5 Hz; the display state comes from the backlight's bl_power or the panel's DRM dpms, and a device with neither is treated as always on). Any fprintd client takes precedence: a Claim cancels the standby verify, a Release re-arms it. Only fingers named in that session owner's map unlock, and the map is re-read at every arm, so a finger deleted while locked stops counting at once. Per-finger no-unlock rules apply here too, and every match is announced as FingerMatched for the session agent. --standby-unlock=off disables it.

Runtime dependencies

The focal64 trustlet is proprietary and is not in this repo. It is extracted from the device's own stock Android partition on first boot by the fp6-vendor-blobs mechanism, the same way other firmware in fp6-img is.

License

GPL-3.0-only, see LICENSE.

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