fix: security and correctness audit fixes (v0.4.1)

PAM conv callback: check msg_style (password only for ECHO_OFF),
handle strdup OOM with proper cleanup, null-check PAM handle.

Fingerprint: self-wire D-Bus g-signal in start() via Rc<RefCell<>>
and connect_local — VerifyStatus signals are now actually dispatched.
VerifyStop before VerifyStart in restart_verify.

Lockscreen: password entry stays active after faillock threshold
(PAM decides lockout, not UI), use Zeroizing<String> from GTK entry.

Release builds exit(1) without ext-session-lock-v1 support.

Config: fingerprint_enabled as Option<bool> so empty user config
does not override system config.

Dead code: remove unused i18n strings and fingerprint accessors,
parameterize faillock_warning max_attempts.

CLAUDE.md

@@ -37,20 +37,23 @@ LD_PRELOAD=/usr/lib/libgtk4-layer-shell.so ./target/release/moonlock
 
 ## Architektur
 
-- `auth.rs` — PAM-Authentifizierung via Raw FFI (unsafe extern "C" conv callback, Zeroizing<Vec<u8>>)
+- `auth.rs` — PAM-Authentifizierung via Raw FFI (unsafe extern "C" conv callback, msg_style-aware, Zeroizing<Vec<u8>>)
-- `fingerprint.rs` — fprintd D-Bus Listener (gio::DBusProxy, VerifyStatus Signal-Handling)
+- `fingerprint.rs` — fprintd D-Bus Listener (Rc<RefCell<FingerprintListener>>, self-wiring g-signal via connect_local)
 - `users.rs` — Aktuellen User via nix getuid, Avatar-Loading mit Symlink-Rejection
 - `power.rs` — Reboot/Shutdown via /usr/bin/loginctl
-- `i18n.rs` — Locale-Erkennung und String-Tabellen (DE/EN)
+- `i18n.rs` — Locale-Erkennung und String-Tabellen (DE/EN), faillock_warning mit konfigurierbarem max_attempts
-- `config.rs` — TOML-Config (background_path, fingerprint_enabled) + Wallpaper-Fallback
+- `config.rs` — TOML-Config (background_path, fingerprint_enabled als Option<bool>) + Wallpaper-Fallback
-- `lockscreen.rs` — GTK4 UI, PAM-Auth via gio::spawn_blocking, Fingerprint-Indikator, Power-Confirm
+- `lockscreen.rs` — GTK4 UI, PAM-Auth via gio::spawn_blocking, Fingerprint-Indikator, Zeroizing<String> für Passwort, Power-Confirm
-- `main.rs` — Entry Point, Panic-Hook, Root-Check, ext-session-lock-v1, Multi-Monitor
+- `main.rs` — Entry Point, Panic-Hook, Root-Check, ext-session-lock-v1 (Pflicht in Release), Multi-Monitor
 
 ## Sicherheit
 
 - ext-session-lock-v1 garantiert: Compositor sperrt alle Surfaces bei lock()
+- Release-Build: Ohne ext-session-lock-v1 wird `exit(1)` aufgerufen — kein Fenster-Fallback
 - Panic-Hook: Bei Crash wird geloggt, aber NIEMALS unlock() aufgerufen — Screen bleibt schwarz
-- Passwort: Zeroizing<Vec<u8>> für sicheres Wiping nach PAM-Callback
+- PAM-Callback: msg_style-aware (Passwort nur bei PAM_PROMPT_ECHO_OFF), strdup-OOM-sicher
+- Passwort: Zeroizing<String> ab GTK-Entry-Extraktion, Zeroizing<Vec<u8>> im PAM-FFI-Layer
 - Root-Check: Exit mit Fehler wenn als root gestartet
+- Faillock: UI-Warnung nach 3 Fehlversuchen, aber PAM entscheidet über Lockout (Entry bleibt aktiv)
 - Kein Schließen per Escape/Alt-F4 — nur durch erfolgreiche PAM-Auth oder Fingerprint
 - GResource-Bundle: CSS/Assets in der Binary kompiliert

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "moonlock"
-version = "0.4.0"
+version = "0.4.1"
 edition = "2024"
 description = "A secure Wayland lockscreen with GTK4, PAM and fingerprint support"
 license = "MIT"

src/auth.rs

@@ -7,6 +7,11 @@ use zeroize::Zeroizing;
 
 // PAM return codes
 const PAM_SUCCESS: i32 = 0;
+const PAM_BUF_ERR: i32 = 5;
+
+// PAM message styles
+const PAM_PROMPT_ECHO_OFF: libc::c_int = 1;
+const PAM_PROMPT_ECHO_ON: libc::c_int = 2;
 
 /// PAM message structure (pam_message).
 #[repr(C)]
@@ -60,7 +65,7 @@ unsafe extern "C" {
 /// which PAM will free. The appdata_ptr must point to a valid CString (the password).
 unsafe extern "C" fn pam_conv_callback(
     num_msg: libc::c_int,
-    _msg: *mut *const PamMessage,
+    msg: *mut *const PamMessage,
     resp: *mut *mut PamResponse,
     appdata_ptr: *mut libc::c_void,
 ) -> libc::c_int {
@@ -83,10 +88,48 @@ unsafe extern "C" fn pam_conv_callback(
         }
 
         for i in 0..num_msg as isize {
-            // Safety: strdup allocates with malloc — PAM will free() the resp strings.
-            // We dereference password which is valid for the lifetime of authenticate().
             let resp_ptr = resp_array.offset(i);
-            (*resp_ptr).resp = libc::strdup((*password).as_ptr());
+            // Safety: msg is an array of pointers provided by PAM
+            let pam_msg = *msg.offset(i);
+            let msg_style = (*pam_msg).msg_style;
+
+            match msg_style {
+                PAM_PROMPT_ECHO_OFF => {
+                    // Password prompt — provide the password via strdup
+                    let dup = libc::strdup((*password).as_ptr());
+                    if dup.is_null() {
+                        // strdup failed (OOM) — free all previously allocated strings
+                        for j in 0..i {
+                            let prev = resp_array.offset(j);
+                            if !(*prev).resp.is_null() {
+                                libc::free((*prev).resp as *mut libc::c_void);
+                            }
+                        }
+                        libc::free(resp_array as *mut libc::c_void);
+                        return PAM_BUF_ERR;
+                    }
+                    (*resp_ptr).resp = dup;
+                }
+                PAM_PROMPT_ECHO_ON => {
+                    // Visible prompt — provide empty string, never the password
+                    let empty = libc::strdup(b"\0".as_ptr() as *const libc::c_char);
+                    if empty.is_null() {
+                        for j in 0..i {
+                            let prev = resp_array.offset(j);
+                            if !(*prev).resp.is_null() {
+                                libc::free((*prev).resp as *mut libc::c_void);
+                            }
+                        }
+                        libc::free(resp_array as *mut libc::c_void);
+                        return PAM_BUF_ERR;
+                    }
+                    (*resp_ptr).resp = empty;
+                }
+                _ => {
+                    // PAM_ERROR_MSG, PAM_TEXT_INFO, or unknown — no response expected
+                    (*resp_ptr).resp = ptr::null_mut();
+                }
+            }
             (*resp_ptr).resp_retcode = 0;
         }
 
@@ -140,7 +183,11 @@ pub fn authenticate(username: &str, password: &str) -> bool {
         return false;
     }
 
-    // Safety: handle is valid after successful pam_start
+    if handle.is_null() {
+        return false;
+    }
+
+    // Safety: handle is valid and non-null after successful pam_start
     let auth_ret = unsafe { pam_authenticate(handle, 0) };
     let acct_ret = if auth_ret == PAM_SUCCESS {
         // Safety: handle is valid, check account restrictions

src/config.rs

@@ -16,24 +16,39 @@ fn default_config_paths() -> Vec<PathBuf> {
     paths
 }
 
+/// Raw deserialization struct — fingerprint_enabled is optional so that
+/// an empty user config does not override the system config's value.
 #[derive(Debug, Clone, Default, Deserialize)]
+struct RawConfig {
+    pub background_path: Option<String>,
+    pub fingerprint_enabled: Option<bool>,
+}
+
+/// Resolved configuration with concrete values.
+#[derive(Debug, Clone)]
 pub struct Config {
     pub background_path: Option<String>,
-    #[serde(default = "default_fingerprint")]
     pub fingerprint_enabled: bool,
 }
 
-fn default_fingerprint() -> bool { true }
+impl Default for Config {
+    fn default() -> Self {
+        Config {
+            background_path: None,
+            fingerprint_enabled: true,
+        }
+    }
+}
 
 pub fn load_config(config_paths: Option<&[PathBuf]>) -> Config {
     let default_paths = default_config_paths();
     let paths = config_paths.unwrap_or(&default_paths);
-    let mut merged = Config { fingerprint_enabled: true, ..Config::default() };
+    let mut merged = Config::default();
     for path in paths {
         if let Ok(content) = fs::read_to_string(path) {
-            if let Ok(parsed) = toml::from_str::<Config>(&content) {
+            if let Ok(parsed) = toml::from_str::<RawConfig>(&content) {
                 if parsed.background_path.is_some() { merged.background_path = parsed.background_path; }
-                merged.fingerprint_enabled = parsed.fingerprint_enabled;
+                if let Some(fp) = parsed.fingerprint_enabled { merged.fingerprint_enabled = fp; }
             }
         }
     }
@@ -57,7 +72,7 @@ pub fn resolve_background_path_with(config: &Config, moonarch_wallpaper: &Path)
 mod tests {
     use super::*;
 
-    #[test] fn default_config() { let c = Config::default(); assert!(c.background_path.is_none()); assert!(!c.fingerprint_enabled); }
+    #[test] fn default_config() { let c = Config::default(); assert!(c.background_path.is_none()); assert!(c.fingerprint_enabled); }
     #[test] fn load_default_fingerprint_true() {
         let dir = tempfile::tempdir().unwrap();
         let conf = dir.path().join("moonlock.toml");
@@ -79,6 +94,15 @@ mod tests {
         let c = Config { background_path: Some(wp.to_str().unwrap().to_string()), fingerprint_enabled: true };
         assert_eq!(resolve_background_path_with(&c, Path::new("/nonexistent")), wp);
     }
+    #[test] fn empty_user_config_preserves_system_fingerprint() {
+        let dir = tempfile::tempdir().unwrap();
+        let sys_conf = dir.path().join("system.toml");
+        let usr_conf = dir.path().join("user.toml");
+        fs::write(&sys_conf, "fingerprint_enabled = false\n").unwrap();
+        fs::write(&usr_conf, "").unwrap();
+        let c = load_config(Some(&[sys_conf, usr_conf]));
+        assert!(!c.fingerprint_enabled);
+    }
     #[test] fn resolve_gresource_fallback() {
         let c = Config::default();
         let r = resolve_background_path_with(&c, Path::new("/nonexistent"));

src/fingerprint.rs

@@ -3,6 +3,8 @@
 
 use gio::prelude::*;
 use gtk4::gio;
+use std::cell::RefCell;
+use std::rc::Rc;
 
 const FPRINTD_BUS_NAME: &str = "net.reactivated.Fprint";
 const FPRINTD_MANAGER_PATH: &str = "/net/reactivated/Fprint/Manager";
@@ -126,24 +128,31 @@ impl FingerprintListener {
         }
     }
 
-    /// Whether the listener is currently running.
-    pub fn is_running(&self) -> bool {
-        self.running
-    }
-
     /// Start listening for fingerprint verification.
-    pub fn start<F, G>(&mut self, username: &str, on_success: F, on_failure: G)
+    /// Connects the D-Bus g-signal handler internally. The `listener` parameter
-    where
+    /// must be the same `Rc<RefCell<FingerprintListener>>` that owns `self`.
+    pub fn start<F, G>(
+        listener: &Rc<RefCell<FingerprintListener>>,
+        username: &str,
+        on_success: F,
+        on_failure: G,
+    ) where
         F: Fn() + 'static,
         G: Fn() + 'static,
     {
-        let proxy = match &self.device_proxy {
+        let proxy = {
-            Some(p) => p,
+            let inner = listener.borrow();
-            None => return,
+            match inner.device_proxy.clone() {
+                Some(p) => p,
+                None => return,
+            }
         };
 
-        self.on_success = Some(Box::new(on_success));
+        {
-        self.on_failure = Some(Box::new(on_failure));
+            let mut inner = listener.borrow_mut();
+            inner.on_success = Some(Box::new(on_success));
+            inner.on_failure = Some(Box::new(on_failure));
+        }
 
         // Claim the device
         let args = glib::Variant::from((&username,));
@@ -178,12 +187,42 @@ impl FingerprintListener {
             return;
         }
 
-        self.running = true;
+        // Connect the g-signal handler on the proxy to dispatch VerifyStatus
+        let listener_weak = Rc::downgrade(listener);
+        let signal_id = proxy.connect_local("g-signal", false, move |values| {
+            // g-signal arguments: (proxy, sender_name, signal_name, parameters)
+            let signal_name: String = match values[2].get() {
+                Ok(v) => v,
+                Err(_) => return None,
+            };
+            if signal_name.as_str() != "VerifyStatus" {
+                return None;
+            }
 
-        // Note: Signal handling is set up by the caller via connect_g_signal()
+            let params = match values[3].get::<glib::Variant>() {
-        // because FingerprintListener is not an Rc and the g-signal callback
+                Ok(v) => v,
-        // needs to reference mutable state. The caller (lockscreen.rs) will
+                Err(_) => return None,
-        // connect the proxy's "g-signal" and call on_verify_status().
+            };
+
+            let status = params
+                .child_value(0)
+                .get::<String>()
+                .unwrap_or_default();
+            let done = params
+                .child_value(1)
+                .get::<bool>()
+                .unwrap_or(false);
+
+            if let Some(listener_rc) = listener_weak.upgrade() {
+                listener_rc.borrow_mut().on_verify_status(&status, done);
+            }
+
+            None
+        });
+
+        let mut inner = listener.borrow_mut();
+        inner.signal_id = Some(signal_id);
+        inner.running = true;
     }
 
     /// Process a VerifyStatus signal from fprintd.
@@ -228,6 +267,14 @@ impl FingerprintListener {
     /// Restart fingerprint verification after a completed attempt.
     fn restart_verify(&self) {
         if let Some(ref proxy) = self.device_proxy {
+            // VerifyStop before VerifyStart to avoid D-Bus errors
+            let _ = proxy.call_sync(
+                "VerifyStop",
+                None,
+                gio::DBusCallFlags::NONE,
+                -1,
+                gio::Cancellable::NONE,
+            );
             let args = glib::Variant::from((&"any",));
             if let Err(e) = proxy.call_sync(
                 "VerifyStart",
@@ -269,15 +316,6 @@ impl FingerprintListener {
         }
     }
 
-    /// Get a reference to the device proxy for signal connection.
-    pub fn device_proxy(&self) -> Option<&gio::DBusProxy> {
-        self.device_proxy.as_ref()
-    }
-
-    /// Store the signal handler ID for cleanup.
-    pub fn set_signal_id(&mut self, id: glib::SignalHandlerId) {
-        self.signal_id = Some(id);
-    }
 }
 
 #[cfg(test)]

src/i18n.rs

@@ -10,13 +10,11 @@ const DEFAULT_LOCALE_CONF: &str = "/etc/locale.conf";
 #[derive(Debug, Clone)]
 pub struct Strings {
     pub password_placeholder: &'static str,
-    pub unlock_button: &'static str,
     pub reboot_tooltip: &'static str,
     pub shutdown_tooltip: &'static str,
     pub fingerprint_prompt: &'static str,
     pub fingerprint_success: &'static str,
     pub fingerprint_failed: &'static str,
-    pub auth_failed: &'static str,
     pub wrong_password: &'static str,
     pub reboot_failed: &'static str,
     pub shutdown_failed: &'static str,
@@ -30,13 +28,11 @@ pub struct Strings {
 
 const STRINGS_DE: Strings = Strings {
     password_placeholder: "Passwort",
-    unlock_button: "Entsperren",
     reboot_tooltip: "Neustart",
     shutdown_tooltip: "Herunterfahren",
     fingerprint_prompt: "Fingerabdruck auflegen zum Entsperren",
     fingerprint_success: "Fingerabdruck erkannt",
     fingerprint_failed: "Fingerabdruck nicht erkannt",
-    auth_failed: "Authentifizierung fehlgeschlagen",
     wrong_password: "Falsches Passwort",
     reboot_failed: "Neustart fehlgeschlagen",
     shutdown_failed: "Herunterfahren fehlgeschlagen",
@@ -50,13 +46,11 @@ const STRINGS_DE: Strings = Strings {
 
 const STRINGS_EN: Strings = Strings {
     password_placeholder: "Password",
-    unlock_button: "Unlock",
     reboot_tooltip: "Reboot",
     shutdown_tooltip: "Shut down",
     fingerprint_prompt: "Place finger on reader to unlock",
     fingerprint_success: "Fingerprint recognized",
     fingerprint_failed: "Fingerprint not recognized",
-    auth_failed: "Authentication failed",
     wrong_password: "Wrong password",
     reboot_failed: "Reboot failed",
     shutdown_failed: "Shutdown failed",
@@ -96,10 +90,9 @@ pub fn load_strings(locale: Option<&str>) -> &'static Strings {
     match locale.as_str() { "de" => &STRINGS_DE, _ => &STRINGS_EN }
 }
 
-pub fn faillock_warning(attempt_count: u32, strings: &Strings) -> Option<String> {
+pub fn faillock_warning(attempt_count: u32, max_attempts: u32, strings: &Strings) -> Option<String> {
-    const MAX: u32 = 3;
+    if attempt_count >= max_attempts { return Some(strings.faillock_locked.to_string()); }
-    if attempt_count >= MAX { return Some(strings.faillock_locked.to_string()); }
+    let remaining = max_attempts - attempt_count;
-    let remaining = MAX - attempt_count;
     if remaining == 1 { return Some(strings.faillock_attempts_remaining.replace("{n}", &remaining.to_string())); }
     None
 }
@@ -133,8 +126,8 @@ mod tests {
         assert!(!s.fingerprint_failed.is_empty());
     }
 
-    #[test] fn faillock_zero() { assert!(faillock_warning(0, load_strings(Some("en"))).is_none()); }
+    #[test] fn faillock_zero() { assert!(faillock_warning(0, 3, load_strings(Some("en"))).is_none()); }
-    #[test] fn faillock_one() { assert!(faillock_warning(1, load_strings(Some("en"))).is_none()); }
+    #[test] fn faillock_one() { assert!(faillock_warning(1, 3, load_strings(Some("en"))).is_none()); }
-    #[test] fn faillock_two() { assert!(faillock_warning(2, load_strings(Some("en"))).is_some()); }
+    #[test] fn faillock_two() { assert!(faillock_warning(2, 3, load_strings(Some("en"))).is_some()); }
-    #[test] fn faillock_three() { assert_eq!(faillock_warning(3, load_strings(Some("en"))).unwrap(), "Account may be locked"); }
+    #[test] fn faillock_three() { assert_eq!(faillock_warning(3, 3, load_strings(Some("en"))).unwrap(), "Account may be locked"); }
 }

src/lockscreen.rs

@@ -10,6 +10,8 @@ use std::cell::RefCell;
 use std::path::Path;
 use std::rc::Rc;
 
+use zeroize::Zeroizing;
+
 use crate::auth;
 use crate::config::Config;
 use crate::fingerprint::FingerprintListener;
@@ -24,6 +26,7 @@ const FAILLOCK_MAX_ATTEMPTS: u32 = 3;
 struct LockscreenState {
     failed_attempts: u32,
     fp_listener: FingerprintListener,
+    fp_listener_rc: Option<Rc<RefCell<FingerprintListener>>>,
 }
 
 /// Create a lockscreen window for a single monitor.
@@ -54,6 +57,7 @@ pub fn create_lockscreen_window(
     let state = Rc::new(RefCell::new(LockscreenState {
         failed_attempts: 0,
         fp_listener,
+        fp_listener_rc: None,
     }));
 
     // Root overlay for background + centered content
@@ -205,7 +209,7 @@ pub fn create_lockscreen_window(
         #[weak]
         password_entry,
         move |entry| {
-            let password = entry.text().to_string();
+            let password = Zeroizing::new(entry.text().to_string());
             if password.is_empty() {
                 return;
             }
@@ -223,14 +227,18 @@ pub fn create_lockscreen_window(
                 password_entry,
                 async move {
                     let user = username.clone();
-                    let pass = password.clone();
+                    let pass = Zeroizing::new((*password).clone());
                     let result = gio::spawn_blocking(move || {
                         auth::authenticate(&user, &pass)
                     }).await;
 
                     match result {
                         Ok(true) => {
-                            state.borrow_mut().fp_listener.stop();
+                            let s = state.borrow();
+                            if let Some(ref fp_rc) = s.fp_listener_rc {
+                                fp_rc.borrow_mut().stop();
+                            }
+                            drop(s);
                             unlock_cb();
                         }
                         _ => {
@@ -241,13 +249,15 @@ pub fn create_lockscreen_window(
                             password_entry.set_text("");
 
                             if count >= FAILLOCK_MAX_ATTEMPTS {
+                                // Show warning but keep entry active — PAM decides lockout
                                 error_label.set_text(strings.faillock_locked);
                                 error_label.set_visible(true);
-                                password_entry.set_sensitive(false);
+                                password_entry.set_sensitive(true);
+                                password_entry.grab_focus();
                             } else {
                                 password_entry.set_sensitive(true);
                                 password_entry.grab_focus();
-                                if let Some(warning) = faillock_warning(count, strings) {
+                                if let Some(warning) = faillock_warning(count, FAILLOCK_MAX_ATTEMPTS, strings) {
                                     error_label.set_text(&warning);
                                 } else {
                                     error_label.set_text(strings.wrong_password);
@@ -325,10 +335,17 @@ pub fn create_lockscreen_window(
             ));
         };
 
-        state
+        // Extract the fp_listener into its own Rc<RefCell<>> for signal self-wiring
-            .borrow_mut()
+        let fp_rc = {
-            .fp_listener
+            let mut s = state.borrow_mut();
-            .start(&user.username, on_success, on_failure);
+            let listener = std::mem::replace(&mut s.fp_listener, FingerprintListener::new());
+            Rc::new(RefCell::new(listener))
+        };
+
+        FingerprintListener::start(&fp_rc, &user.username, on_success, on_failure);
+
+        // Store back the Rc reference for stop() on unlock
+        state.borrow_mut().fp_listener_rc = Some(fp_rc);
     }
 
     // Fade-in on map

src/main.rs

@@ -43,8 +43,16 @@ fn activate(app: &gtk::Application) {
     if gtk4_session_lock::is_supported() {
         activate_with_session_lock(app, &display, &bg_path, &config);
     } else {
-        log::warn!("ext-session-lock-v1 not supported — running in development mode");
+        #[cfg(debug_assertions)]
-        activate_without_lock(app, &bg_path, &config);
+        {
+            log::warn!("ext-session-lock-v1 not supported — running in development mode");
+            activate_without_lock(app, &bg_path, &config);
+        }
+        #[cfg(not(debug_assertions))]
+        {
+            log::error!("ext-session-lock-v1 not supported — refusing to run without session lock");
+            std::process::exit(1);
+        }
     }
 }
 
@@ -90,6 +98,7 @@ fn activate_with_session_lock(
     }
 }
 
+#[cfg(debug_assertions)]
 fn activate_without_lock(
     app: &gtk::Application,
     bg_path: &PathBuf,