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Third triple audit (quality, performance, security). Key fixes: - Blur padding offset: texture at (-pad,-pad) prevents edge darkening on all sides - Wallpaper loads after lock.lock() — disk I/O no longer delays lock acquisition - begin_verification disconnects old signal handler before registering new one - resume_async resets failed_attempts to prevent premature exhaustion - Unknown VerifyStatus with done=true triggers restart instead of hanging - symlink_metadata() replaces separate is_file()+is_symlink() (TOCTOU) - faillock_warning dead code removed, blur sigma clamped to [0,100] - Redundant Zeroizing<Vec<u8>> removed, on_verify_status restricted to pub(crate) - Warn logging for non-UTF-8 GECOS and avatar path errors - Default impl for FingerprintListener, 3 new tests (47 total)
53 lines
6.3 KiB
Markdown
53 lines
6.3 KiB
Markdown
# Decisions
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Architectural and design decisions for Moonlock, in reverse chronological order.
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## 2026-03-30 – Third audit: blur offset, lock-before-IO, FP signal lifecycle, TOCTOU
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- **Who**: Nyx, Dom
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- **Why**: Third triple audit (quality, performance, security) found: blur padding offset rendering texture at (0,0) instead of (-pad,-pad) causing edge darkening on left/top (BUG), wallpaper disk I/O blocking before lock() extending the unsecured window (PERF/SEC), signal handler duplication on resume_async (SEC), failed_attempts not reset on FP resume (SEC), unknown VerifyStatus with done=false hanging FP listener (SEC), TOCTOU in is_file+is_symlink checks (SEC), dead code in faillock_warning (QUALITY), unbounded blur sigma (SEC).
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- **Tradeoffs**: Wallpaper loads after lock() — screen briefly shows without wallpaper until texture is ready. Acceptable: security > aesthetics. Blur sigma clamped to [0.0, 100.0] — arbitrary upper bound but prevents GPU memory exhaustion.
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- **How**: (1) Texture offset to (-pad, -pad) in render_blurred_texture. (2) lock.lock() before resolve_background_path. (3) begin_verification disconnects old signal_id before registering new. (4) resume_async resets failed_attempts. (5) Unknown VerifyStatus with done=true triggers restart. (6) symlink_metadata() for atomic file+symlink check. (7) faillock_warning dead code removed, saturating_sub. (8) background_blur clamped. (9) Redundant Zeroizing<Vec<u8>> removed. (10) Default impl for FingerprintListener. (11) on_verify_status restricted to pub(crate). (12) Warn logging for non-UTF-8 GECOS and avatar paths.
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## 2026-03-30 – Second audit: zeroize CString, FP account check, PAM timeout, blur downscale
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- **Who**: Nyx, Dom
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- **Why**: Second triple audit (quality, performance, security) found: CString password copy not zeroized (HIGH), fingerprint unlock bypassing pam_acct_mgmt (MEDIUM), no PAM timeout leaving user locked out on hanging modules (MEDIUM), GPU blur on full wallpaper resolution (MEDIUM), no-monitor edge case doing `return` instead of `exit(1)` (MEDIUM).
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- **Tradeoffs**: PAM timeout (30s) uses a generation counter to avoid stale result interference — adds complexity but prevents parallel PAM sessions. FP restart after failed account check re-claims the device, adding a D-Bus round-trip, but prevents permanent FP death on transient failures. Blur downscale to 1920px cap trades negligible quality for ~4x less GPU work on 4K wallpapers.
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- **How**: (1) `Zeroizing<CString>` wraps password in auth.rs, `zeroize/std` feature enabled. (2) `check_account()` calls pam_acct_mgmt after FP match; `resume_async()` restarts FP on transient failure. (3) `auth_generation` counter invalidates stale PAM results; 30s timeout re-enables UI. (4) `MAX_BLUR_DIMENSION` caps blur input at 1920px, sigma scaled proportionally. (5) `exit(1)` on no-monitor after `lock.lock()`.
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## 2026-03-28 – Remove embedded wallpaper from binary
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- **Who**: Nyx, Dom
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- **Why**: Wallpaper is installed by moonarch to /usr/share/moonarch/wallpaper.jpg. Embedding a 374K JPEG in the binary is redundant. GTK background color (Catppuccin Mocha base) is a clean fallback.
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- **Tradeoffs**: Without moonarch installed AND without config, lockscreen shows plain dark background instead of wallpaper. Acceptable — that's the expected minimal state.
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- **How**: Remove wallpaper.jpg from GResources, return None from resolve_background_path when no file found, skip background picture creation when no texture available.
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## 2026-03-28 – Audit-driven security and lifecycle fixes (v0.6.0)
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- **Who**: Nyx, Dom
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- **Why**: Triple audit (quality, performance, security) revealed a critical D-Bus signal spoofing vector, fingerprint lifecycle bugs, and multi-monitor performance issues.
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- **Tradeoffs**: `cleanup_dbus()` extraction adds a method but clarifies the stop/match ownership; `running_flag: Rc<Cell<bool>>` adds a field but prevents race between async restart and stop; sender validation adds a check per signal but closes the only known auth bypass.
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- **How**: (1) Validate D-Bus VerifyStatus sender against fprintd's unique bus name. (2) Extract `cleanup_dbus()` from `stop()`, call it on verify-match. (3) `Rc<Cell<bool>>` running flag checked after await in `restart_verify_async`. (4) Consistent 3s D-Bus timeouts. (5) Panic hook before logging. (6) Blur and avatar caches shared across monitors. (7) Peek icon disabled. (8) Symlink rejection for background_path. (9) TOML parse errors logged.
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## 2026-03-28 – GPU blur via GskBlurNode replaces CPU blur
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- **Who**: Nyx, Dom
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- **Why**: CPU-side Gaussian blur (`image` crate) blocked the GTK main thread for 500ms–2s on 4K wallpapers at cold cache. Disk cache mitigated repeat starts but added ~100 lines of complexity.
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- **Tradeoffs**: GPU blur quality is slightly different (box-blur approximation vs true Gaussian), acceptable for wallpaper. Removes `image` and `dirs` dependencies entirely. No disk cache needed.
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- **How**: `Snapshot::push_blur()` + `GskRenderer::render_texture()` on `connect_realize`. Blur happens once on the GPU when the widget gets its renderer, producing a concrete `gdk::Texture`. Zero startup latency.
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## 2026-03-28 – Optional background blur via `image` crate (superseded)
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- **Who**: Nyx, Dom
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- **Why**: Consistent with moonset/moongreet — blurred wallpaper as lockscreen background is a common UX pattern
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- **Tradeoffs**: Adds `image` crate dependency (~15 transitive crates); CPU-side Gaussian blur at load time adds startup latency proportional to image size and sigma. Acceptable because blur runs once and the texture is shared across monitors.
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- **How**: `load_background_texture(bg_path, blur_radius)` loads texture, optionally applies `imageops::blur()`, returns `gdk::Texture`. Config option `background_blur: Option<f32>` in TOML.
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## 2026-03-28 – Shared wallpaper texture pattern (aligned with moonset/moongreet)
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- **Who**: Nyx, Dom
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- **Why**: Previously loaded wallpaper per-window via `Picture::for_filename()`. Multi-monitor setups decoded the JPEG redundantly. Blur feature requires texture pixel access anyway.
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- **Tradeoffs**: Slightly more code in main.rs (texture loaded before window creation), but avoids redundant decoding and enables the blur feature.
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- **How**: `load_background_texture()` in lockscreen.rs decodes once, `create_background_picture()` wraps shared `gdk::Texture` in `gtk::Picture`. Same pattern as moonset/moongreet.
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