fix: Audit-Findings — Realize-Handler, Thread-Safety, Input-Validierung

- _on_realize implementiert (war nur connected, nicht definiert)
- do_unrealize für as_file() Context-Manager-Cleanup
- threading.Lock für _greetd_sock Race Condition
- TOML-Parsing-Fehler abfangen statt Crash
- last-user Datei: Längen- und Zeichenvalidierung
- detect_locale: non-alpha LANG-Werte abweisen
- exec_cmd Plausibility-Check mit shutil.which
- Exception-Details ins Log statt in die UI
- subprocess.run Timeout für Power-Actions
- Sequence[Path] statt tuple[Path, ...] in get_sessions
- Mock-Server _recvall für fragmentierte Reads
- [behavior]-Config-Sektion entfernt (unimplementiert)
- Design Decisions in CLAUDE.md dokumentiert

src/moongreet/config.py

@@ -33,8 +33,11 @@ def load_config(config_path: Path | None = None) -> Config:
     if not config_path.exists():
         return Config()
 
-    with open(config_path, "rb") as f:
-        data = tomllib.load(f)
+    try:
+        with open(config_path, "rb") as f:
+            data = tomllib.load(f)
+    except (tomllib.TOMLDecodeError, OSError):
+        return Config()
 
     config = Config()
     appearance = data.get("appearance", {})

src/moongreet/greeter.py

@@ -1,8 +1,11 @@
 # ABOUTME: Main greeter window — builds the GTK4 UI layout for the Moongreet greeter.
 # ABOUTME: Handles user selection, session choice, password entry, and power actions.
 
+import logging
 import os
+import re
 import shlex
+import shutil
 import socket
 import stat
 import subprocess
@@ -22,8 +25,12 @@ from moongreet.users import User, get_users, get_avatar_path, get_user_gtk_theme
 from moongreet.sessions import Session, get_sessions
 from moongreet.power import reboot, shutdown
 
+logger = logging.getLogger(__name__)
+
 LAST_USER_PATH = Path("/var/cache/moongreet/last-user")
 FAILLOCK_MAX_ATTEMPTS = 3
+VALID_USERNAME = re.compile(r"^[a-zA-Z0-9_.-]+$")
+MAX_USERNAME_LENGTH = 256
 PACKAGE_DATA = files("moongreet") / "data"
 DEFAULT_AVATAR_PATH = PACKAGE_DATA / "default-avatar.svg"
 DEFAULT_WALLPAPER_PATH = PACKAGE_DATA / "wallpaper.jpg"
@@ -56,13 +63,33 @@ class GreeterWindow(Gtk.ApplicationWindow):
         self._sessions = get_sessions()
         self._selected_user: User | None = None
         self._greetd_sock: socket.socket | None = None
+        self._greetd_sock_lock = threading.Lock()
         self._default_avatar_pixbuf: GdkPixbuf.Pixbuf | None = None
         self._avatar_cache: dict[str, GdkPixbuf.Pixbuf] = {}
         self._failed_attempts: dict[str, int] = {}
+        self._wallpaper_ctx = None
 
         self._build_ui()
-        self._select_initial_user()
         self._setup_keyboard_navigation()
+        # Defer initial user selection until the window is realized,
+        # so get_color() returns the actual theme foreground for SVG tinting
+        self.connect("realize", self._on_realize)
+
+    def _on_realize(self, widget: Gtk.Widget) -> None:
+        """Called when the window is realized — select initial user.
+
+        Deferred from __init__ so get_color() returns actual theme values
+        for SVG tinting. Uses idle_add so the first frame renders before
+        avatar loading blocks the main loop.
+        """
+        GLib.idle_add(self._select_initial_user)
+
+    def do_unrealize(self) -> None:
+        """Clean up resources when the window is unrealized."""
+        if self._wallpaper_ctx is not None:
+            self._wallpaper_ctx.__exit__(None, None, None)
+            self._wallpaper_ctx = None
+        super().do_unrealize()
 
     def _build_ui(self) -> None:
         """Build the complete greeter UI layout."""
@@ -375,12 +402,13 @@ class GreeterWindow(Gtk.ApplicationWindow):
 
     def _close_greetd_sock(self) -> None:
         """Close the greetd socket and reset the reference."""
-        if self._greetd_sock:
-            try:
-                self._greetd_sock.close()
-            except OSError:
-                pass
-            self._greetd_sock = None
+        with self._greetd_sock_lock:
+            if self._greetd_sock:
+                try:
+                    self._greetd_sock.close()
+                except OSError:
+                    pass
+                self._greetd_sock = None
 
     def _set_login_sensitive(self, sensitive: bool) -> None:
         """Enable or disable login controls during authentication."""
@@ -412,7 +440,8 @@ class GreeterWindow(Gtk.ApplicationWindow):
             sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
             sock.settimeout(10.0)
             sock.connect(sock_path)
-            self._greetd_sock = sock
+            with self._greetd_sock_lock:
+                self._greetd_sock = sock
 
             # Step 1: Create session
             response = create_session(sock, user.username)
@@ -440,7 +469,7 @@ class GreeterWindow(Gtk.ApplicationWindow):
             # Step 3: Start session
             if response.get("type") == "success":
                 cmd = shlex.split(session.exec_cmd)
-                if not cmd:
+                if not cmd or not shutil.which(cmd[0]):
                     cancel_session(sock)
                     GLib.idle_add(self._on_login_error, None, self._strings.invalid_session_command)
                     return
@@ -457,11 +486,13 @@ class GreeterWindow(Gtk.ApplicationWindow):
             self._close_greetd_sock()
 
         except ConnectionError as e:
+            logger.error("greetd connection error: %s", e)
             self._close_greetd_sock()
-            GLib.idle_add(self._on_login_error, None, self._strings.connection_error.format(error=e))
+            GLib.idle_add(self._on_login_error, None, self._strings.connection_error)
         except (OSError, ValueError) as e:
+            logger.error("greetd socket error: %s", e)
             self._close_greetd_sock()
-            GLib.idle_add(self._on_login_error, None, self._strings.socket_error.format(error=e))
+            GLib.idle_add(self._on_login_error, None, self._strings.socket_error)
 
     def _on_login_error(self, response: dict | None, message: str) -> None:
         """Handle login error on the GTK main thread."""
@@ -483,12 +514,13 @@ class GreeterWindow(Gtk.ApplicationWindow):
 
     def _cancel_pending_session(self) -> None:
         """Cancel any in-progress greetd session."""
-        if self._greetd_sock:
-            try:
-                cancel_session(self._greetd_sock)
-            except (ConnectionError, OSError):
-                pass
-            self._close_greetd_sock()
+        with self._greetd_sock_lock:
+            if self._greetd_sock:
+                try:
+                    cancel_session(self._greetd_sock)
+                except (ConnectionError, OSError):
+                    pass
+        self._close_greetd_sock()
 
     def _get_selected_session(self) -> Session | None:
         """Get the currently selected session from the dropdown."""
@@ -535,9 +567,12 @@ class GreeterWindow(Gtk.ApplicationWindow):
         """Load the last logged-in username from cache."""
         if LAST_USER_PATH.exists():
             try:
-                return LAST_USER_PATH.read_text().strip()
+                username = LAST_USER_PATH.read_text().strip()
             except OSError:
                 return None
+            if len(username) > MAX_USERNAME_LENGTH or not VALID_USERNAME.match(username):
+                return None
+            return username
         return None
 
     @staticmethod

src/moongreet/i18n.py

@@ -31,9 +31,11 @@ class Strings:
     reboot_failed: str
     shutdown_failed: str
 
-    # Templates (use .format())
+    # Error messages (continued)
     connection_error: str
     socket_error: str
+
+    # Templates (use .format())
     faillock_attempts_remaining: str
     faillock_locked: str
 
@@ -54,8 +56,8 @@ _STRINGS_DE = Strings(
     session_start_failed="Session konnte nicht gestartet werden",
     reboot_failed="Neustart fehlgeschlagen",
     shutdown_failed="Herunterfahren fehlgeschlagen",
-    connection_error="Verbindungsfehler: {error}",
-    socket_error="Socket-Fehler: {error}",
+    connection_error="Verbindungsfehler",
+    socket_error="Socket-Fehler",
     faillock_attempts_remaining="Noch {n} Versuch(e) vor Kontosperrung!",
     faillock_locked="Konto ist möglicherweise gesperrt",
 )
@@ -76,8 +78,8 @@ _STRINGS_EN = Strings(
     session_start_failed="Failed to start session",
     reboot_failed="Reboot failed",
     shutdown_failed="Shutdown failed",
-    connection_error="Connection error: {error}",
-    socket_error="Socket error: {error}",
+    connection_error="Connection error",
+    socket_error="Socket error",
     faillock_attempts_remaining="{n} attempt(s) remaining before lockout!",
     faillock_locked="Account may be locked",
 )
@@ -102,7 +104,9 @@ def detect_locale(locale_conf_path: Path = DEFAULT_LOCALE_CONF) -> str:
         return "en"
 
     # Extract language prefix: "de_DE.UTF-8" → "de"
-    lang = lang.split("_")[0].split(".")[0]
+    lang = lang.split("_")[0].split(".")[0].lower()
+    if not lang.isalpha():
+        return "en"
     return lang
 
 

src/moongreet/power.py

@@ -4,11 +4,14 @@
 import subprocess
 
 
+POWER_TIMEOUT = 30
+
+
 def reboot() -> None:
     """Reboot the system via loginctl."""
-    subprocess.run(["loginctl", "reboot"], check=True)
+    subprocess.run(["loginctl", "reboot"], check=True, timeout=POWER_TIMEOUT)
 
 
 def shutdown() -> None:
     """Shut down the system via loginctl."""
-    subprocess.run(["loginctl", "poweroff"], check=True)
+    subprocess.run(["loginctl", "poweroff"], check=True, timeout=POWER_TIMEOUT)

src/moongreet/sessions.py

@@ -2,6 +2,7 @@
 # ABOUTME: Parses .desktop files from standard session directories.
 
 import configparser
+from collections.abc import Sequence
 from dataclasses import dataclass
 from pathlib import Path
 
@@ -37,8 +38,8 @@ def _parse_desktop_file(path: Path, session_type: str) -> Session | None:
 
 
 def get_sessions(
-    wayland_dirs: tuple[Path, ...] = DEFAULT_WAYLAND_DIRS,
-    xsession_dirs: tuple[Path, ...] = DEFAULT_XSESSION_DIRS,
+    wayland_dirs: Sequence[Path] = DEFAULT_WAYLAND_DIRS,
+    xsession_dirs: Sequence[Path] = DEFAULT_XSESSION_DIRS,
 ) -> list[Session]:
     """Discover available sessions from .desktop files."""
     sessions: list[Session] = []