fix: audit LOW fixes — docs, rustdoc, scope, debug gate, lto fat (v0.6.12)

- Update CLAUDE.md and README.md to reflect the blur range [0,200] that
  the code has clamped to since v0.6.8.
- Move the // SYNC: comment above the /// doc on MAX_BLUR_DIMENSION so
  rustdoc renders one coherent paragraph instead of a truncated sentence.
- Narrow check_account visibility to pub(crate) and document the caller
  precondition (username must come from users::get_current_user()).
- Gate MOONLOCK_DEBUG behind #[cfg(debug_assertions)]. Release builds
  always run at LevelFilter::Info so a session script cannot escalate
  journal verbosity to leak fprintd / D-Bus internals.
- Document why pam_setcred is deliberately not called in authenticate().
- Release profile: lto = "fat" instead of "thin" — doubles release build
  time for better cross-crate inlining on the auth + i18n hot paths.

CLAUDE.md

@@ -40,7 +40,7 @@ LD_PRELOAD=/usr/lib/libgtk4-layer-shell.so ./target/release/moonlock
 - `users.rs` — Aktuellen User via nix getuid, Avatar-Loading mit Symlink-Rejection
 - `power.rs` — Reboot/Shutdown via /usr/bin/systemctl
 - `i18n.rs` — Locale-Erkennung (OnceLock-cached) und String-Tabellen (DE/EN), faillock_warning mit konfigurierbarem max_attempts
-- `config.rs` — TOML-Config (background_path, background_blur clamped [0,100], fingerprint_enabled als Option<bool>) + Wallpaper-Fallback + Symlink-Rejection via symlink_metadata + Parse-Error-Logging
+- `config.rs` — TOML-Config (background_path, background_blur clamped [0,200], fingerprint_enabled als Option<bool>) + Wallpaper-Fallback + Symlink-Rejection via symlink_metadata + Parse-Error-Logging
 - `lockscreen.rs` — GTK4 UI via LockscreenHandles, PAM-Auth via gio::spawn_blocking mit 30s Timeout und Generation Counter, FP-Label/Start separat verdrahtet mit pam_acct_mgmt-Check und auto-resume, Zeroizing<String> für Passwort, Power-Confirm, GPU-Blur via GskBlurNode (Downscale auf max 1920px), Blur/Avatar-Cache für Multi-Monitor
 - `main.rs` — Entry Point, Panic-Hook (vor Logging), Root-Check, ext-session-lock-v1 (Pflicht in Release), Monitor-Hotplug via `connect_monitor`-Signal (v1_2), shared Blur/Avatar-Caches in Rc, systemd-Journal-Logging, Debug-Level per `MOONLOCK_DEBUG` Env-Var, async fprintd-Init nach window.present()
 

Cargo.lock

@@ -575,7 +575,7 @@ dependencies = [
 
 [[package]]
 name = "moonlock"
-version = "0.6.11"
+version = "0.6.12"
 dependencies = [
  "gdk-pixbuf",
  "gdk4",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "moonlock"
-version = "0.6.11"
+version = "0.6.12"
 edition = "2024"
 description = "A secure Wayland lockscreen with GTK4, PAM and fingerprint support"
 license = "MIT"
@@ -28,6 +28,6 @@ tempfile = "3"
 glib-build-tools = "0.22"
 
 [profile.release]
-lto = "thin"
+lto = "fat"
 codegen-units = 1
 strip = true

DECISIONS.md

@@ -2,6 +2,13 @@
 
 Architectural and design decisions for Moonlock, in reverse chronological order.
 
+## 2026-04-24 – Audit LOW fixes: docs, rustdoc, check_account scope, debug gating, lto fat (v0.6.12)
+
+- **Who**: ClaudeCode, Dom
+- **Why**: Six LOW findings cleared in a single pass. (1) Docs referenced the old `[0,100]` blur range; code clamps `[0,200]` since v0.6.8. (2) The `MAX_BLUR_DIMENSION` doc comment was split by a `// SYNC:` block, producing a truncated sentence in rustdoc. (3) `check_account` was `pub` and relied on callers only ever passing `getuid()`-derived usernames; the contract was not enforced by the type system. (4) `MOONLOCK_DEBUG` env var flipped log verbosity to Debug in release builds, letting a compromised session script escalate journal noise about fprintd / D-Bus. (5) `pam_setcred` absence was undocumented. (6) `[profile.release]` used `lto = "thin"` — fine for most crates, but for a latency-critical auth binary compiled once per release, fat LTO's extra cross-crate inlining is worth the ~1 min build hit.
+- **Tradeoffs**: `lto = "fat"` roughly doubles release build time (~30 s → ~60 s) for slightly better inlining across PAM FFI wrappers and the i18n/status paths. `#[cfg(debug_assertions)]` on the debug-level selector means you have to run a debug build to raise log level — inconvenient for live troubleshooting, but aligned with the security-first posture.
+- **How**: (1) `CLAUDE.md` + `README.md` updated to `[0,200]`. (2) `// SYNC:` block moved above the `///` doc so rustdoc renders one coherent paragraph. (3) `check_account` visibility narrowed to `pub(crate)` with a `Precondition` paragraph explaining the username contract. (4) Debug-level selection wrapped in `#[cfg(debug_assertions)]`; release builds always run at `LevelFilter::Info`. (5) Added a comment block in `authenticate()` documenting why `pam_setcred` is deliberately absent and where it would hook in if needed. (6) `lto = "fat"` in `Cargo.toml`.
+
 ## 2026-04-24 – Audit MEDIUM fixes: D-Bus cleanup race, TOCTOU open, FP reset, GTK entry clear (v0.6.11)
 
 - **Who**: ClaudeCode, Dom

README.md

@@ -9,7 +9,7 @@ Part of the Moonarch ecosystem.
 - **PAM authentication** — Uses system PAM stack (`/etc/pam.d/moonlock`) with 30s timeout and generation counter
 - **Fingerprint unlock** — fprintd D-Bus integration with sender validation, async init (window appears instantly), `pam_acct_mgmt` check after verify, auto-resume on transient errors
 - **Multi-monitor + hotplug** — Lockscreen on every monitor with shared blur and avatar caches; monitors added after suspend/resume get windows automatically via `connect_monitor` signal
-- **GPU blur** — Background blur via GskBlurNode (downscale to max 1920px, configurable 0–100)
+- **GPU blur** — Background blur via GskBlurNode (downscale to max 1920px, configurable 0–200)
 - **i18n** — German and English (auto-detected)
 - **Faillock warning** — Progressive UI warning after failed attempts, PAM decides lockout
 - **Panic safety** — Panic hook logs but never unlocks (installed before logging)
@@ -48,7 +48,7 @@ Create `/etc/moonlock/moonlock.toml` or `~/.config/moonlock/moonlock.toml`:
 
 ```toml
 background_path = "/usr/share/wallpapers/moon.jpg"
-background_blur = 40.0    # 0.0–100.0, optional
+background_blur = 40.0    # 0.0–200.0, optional
 fingerprint_enabled = true
 ```
 

src/auth.rs

@@ -191,7 +191,12 @@ pub fn authenticate(username: &str, password: &str) -> bool {
         return false;
     }
 
-    // Safety: handle is valid and non-null after successful pam_start
+    // Safety: handle is valid and non-null after successful pam_start.
+    // Note: pam_setcred is intentionally NOT called here. A lockscreen unlocks
+    // an existing session whose credentials were already established at login;
+    // refreshing them would duplicate work done by the session's login manager.
+    // If per-unlock credential refresh (Kerberos tickets, pam_gnome_keyring)
+    // is ever desired, hook it here with PAM_ESTABLISH_CRED.
     let auth_ret = unsafe { pam_authenticate(handle, 0) };
     let acct_ret = if auth_ret == PAM_SUCCESS {
         // Safety: handle is valid, check account restrictions
@@ -211,7 +216,12 @@ pub fn authenticate(username: &str, password: &str) -> bool {
 /// Used after fingerprint unlock to enforce account policies (lockout, expiry)
 /// that would otherwise be bypassed when not going through pam_authenticate.
 /// Returns true if the account is valid and allowed to log in.
-pub fn check_account(username: &str) -> bool {
+///
+/// **Precondition**: `username` must be the authenticated system user, derived
+/// via `users::get_current_user()` (which reads `getuid()`). Calling this with
+/// an attacker-controlled username is unsafe — `pam_acct_mgmt` returns SUCCESS
+/// for any valid unlocked account, giving a trivial unlock bypass.
+pub(crate) fn check_account(username: &str) -> bool {
     let service = match CString::new("moonlock") {
         Ok(c) => c,
         Err(_) => return false,

src/lockscreen.rs

@@ -592,11 +592,11 @@ fn create_background_picture(
     background
 }
 
-/// Maximum texture dimension for blur input. Textures larger than this are
 // SYNC: MAX_BLUR_DIMENSION, render_blurred_texture, and create_background_picture
 // are duplicated in moongreet/src/greeter.rs and moonset/src/panel.rs.
 // Changes here must be mirrored to the other two projects.
 
+/// Maximum texture dimension for blur input. Textures larger than this are
 /// downscaled before blurring — the blur destroys detail anyway, so there is
 /// no visible quality loss, but GPU work is reduced significantly.
 const MAX_BLUR_DIMENSION: f32 = 1920.0;

src/main.rs

@@ -250,11 +250,17 @@ fn setup_logging() {
             eprintln!("Failed to create journal logger: {e}");
         }
     }
+    // Debug level is only selectable in debug builds. Release binaries ignore
+    // MOONLOCK_DEBUG so a session script cannot escalate log verbosity to leak
+    // fprintd / D-Bus internals into the journal.
+    #[cfg(debug_assertions)]
     let level = if std::env::var("MOONLOCK_DEBUG").is_ok() {
         log::LevelFilter::Debug
     } else {
         log::LevelFilter::Info
     };
+    #[cfg(not(debug_assertions))]
+    let level = log::LevelFilter::Info;
     log::set_max_level(level);
 }