use unpatched qt for dev tooling (fmt, lint, devshell)

flake.nix

@@ -55,8 +55,9 @@
         nixpkgs.lib.genAttrs systems (
           system:
           fn rec {
-            pkgs = (nixpkgs.legacyPackages.${system}).extend qtbaseOverlay;
-            treefmt-eval = treefmt-nix.lib.evalModule pkgs treefmt-config;
+            rawPkgs = nixpkgs.legacyPackages.${system};
+            pkgs = rawPkgs.extend qtbaseOverlay;
+            treefmt-eval = treefmt-nix.lib.evalModule rawPkgs treefmt-config;
           }
         );
     in
@@ -64,7 +65,7 @@
       formatter = forAllSystems ({ treefmt-eval, ... }: treefmt-eval.config.build.wrapper);
 
       packages = forAllSystems (
-        { pkgs, ... }:
+        { pkgs, rawPkgs, ... }:
         let
           # Rebuild quickshell against patched Qt via its overlay
           qs = (pkgs.extend quickshell.overlays.default).quickshell.override {
@@ -87,14 +88,37 @@
           '';
           docs = pkgs.callPackage ./nix/docs.nix { inherit self; };
           default = nova-shell;
+
+          # Reproducer for the qtbase wayland screen UAF, built twice:
+          # patched (should survive) and unpatched (should crash).
+          screen-uaf-reproducer-patched = pkgs.stdenv.mkDerivation {
+            pname = "screen-uaf-reproducer-patched";
+            version = "0";
+            src = ./test/screen-uaf-reproducer;
+            nativeBuildInputs = [
+              pkgs.cmake
+              pkgs.qt6.wrapQtAppsHook
+            ];
+            buildInputs = [ pkgs.qt6.qtbase ];
+          };
+          screen-uaf-reproducer-unpatched = rawPkgs.stdenv.mkDerivation {
+            pname = "screen-uaf-reproducer-unpatched";
+            version = "0";
+            src = ./test/screen-uaf-reproducer;
+            nativeBuildInputs = [
+              rawPkgs.cmake
+              rawPkgs.qt6.wrapQtAppsHook
+            ];
+            buildInputs = [ rawPkgs.qt6.qtbase ];
+          };
         }
       );
 
       devShells = forAllSystems (
-        { pkgs, ... }:
+        { rawPkgs, ... }:
         {
-          default = pkgs.mkShell {
-            packages = with pkgs; [
+          default = rawPkgs.mkShell {
+            packages = with rawPkgs; [
               cargo
               rustc
               rust-analyzer
@@ -108,21 +132,25 @@
       );
 
       checks = forAllSystems (
-        { pkgs, treefmt-eval }:
+        {
+          pkgs,
+          rawPkgs,
+          treefmt-eval,
+        }:
         {
           formatting = treefmt-eval.config.build.check self;
           build = self.packages.${pkgs.stdenv.hostPlatform.system}.default;
           nova-stats = self.packages.${pkgs.stdenv.hostPlatform.system}.nova-stats;
           docs = self.packages.${pkgs.stdenv.hostPlatform.system}.docs;
           qmllint =
-            pkgs.runCommand "nova-shell-qmllint"
+            rawPkgs.runCommand "nova-shell-qmllint"
               {
-                nativeBuildInputs = [ pkgs.qt6.qtdeclarative ];
+                nativeBuildInputs = [ rawPkgs.qt6.qtdeclarative ];
                 src = self;
               }
               ''
                 cd $src
-                export QML_IMPORT_PATH="${pkgs.qt6.qtdeclarative}/lib/qt-6/qml:${
+                export QML_IMPORT_PATH="${rawPkgs.qt6.qtdeclarative}/lib/qt-6/qml:${
                   quickshell.packages.${pkgs.stdenv.hostPlatform.system}.default
                 }/lib/qt-6/qml"
                 qmllint -E \

test/screen-uaf-reproducer/CMakeLists.txt

@@ -0,0 +1,9 @@
+cmake_minimum_required(VERSION 3.19)
+project(screen-uaf-reproducer LANGUAGES CXX)
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_AUTOMOC ON)
+
+find_package(Qt6 REQUIRED COMPONENTS Gui)
+add_executable(screen-uaf-reproducer main.cpp)
+target_link_libraries(screen-uaf-reproducer PRIVATE Qt6::Gui)

test/screen-uaf-reproducer/main.cpp

@@ -0,0 +1,63 @@
+// Minimal reproducer for Qt 6 Wayland screen use-after-free.
+//
+// Bug: libwayland resolves wl_output proxy pointers at demarshal time (when
+// events are read from the socket). If wl_registry.global_remove and
+// wl_surface.enter/leave for the same output arrive in the same dispatch
+// batch, the surface event handler receives a dangling proxy pointer.
+// QWaylandScreen::fromWlOutput() reads stale userdata from the freed proxy
+// and returns a garbage QWaylandScreen*, which crashes on dereference.
+//
+// Build:
+//   cmake -B build && cmake --build build
+//
+// Run (on any wlroots-based compositor or Niri):
+//   ./build/screen-uaf-reproducer &
+//   # then toggle an output off/on rapidly, e.g.:
+//   #   wlr-randr --output eDP-1 --off && wlr-randr --output eDP-1 --on
+//   #   niri msg action power-off-monitors  (then move mouse to wake)
+//   # or just unplug/replug an external monitor
+//
+// The crash typically occurs within seconds of the output toggle.
+// Creating many surfaces increases the odds that a surface.leave event
+// lands in the same batch as the global_remove.
+
+#include <QGuiApplication>
+#include <QScreen>
+#include <QWindow>
+#include <QTimer>
+#include <vector>
+#include <cstdio>
+
+int main(int argc, char *argv[])
+{
+    QGuiApplication app(argc, argv);
+
+    // Many surfaces = higher chance of batched enter/leave events
+    constexpr int kWindows = 20;
+    std::vector<std::unique_ptr<QWindow>> windows;
+    windows.reserve(kWindows);
+
+    for (int i = 0; i < kWindows; ++i) {
+        auto w = std::make_unique<QWindow>();
+        w->setTitle(QStringLiteral("uaf-%1").arg(i));
+        w->resize(1, 1);
+        w->setFlag(Qt::ToolTip); // small, no decoration, no focus
+        w->show();
+        windows.push_back(std::move(w));
+    }
+
+    std::fprintf(stderr,
+        "screen-uaf-reproducer: %d surfaces created on %d screen(s).\n"
+        "Toggle an output off/on to trigger the crash.\n",
+        kWindows, QGuiApplication::screens().size());
+
+    // Log screen changes so we know when the toggle happens
+    QObject::connect(&app, &QGuiApplication::screenAdded, [](QScreen *s) {
+        std::fprintf(stderr, "  screenAdded: %s\n", qPrintable(s->name()));
+    });
+    QObject::connect(&app, &QGuiApplication::screenRemoved, [](QScreen *s) {
+        std::fprintf(stderr, "  screenRemoved: %s\n", qPrintable(s->name()));
+    });
+
+    return app.exec();
+}

test/screen-uaf-reproducer/shell.nix

@@ -0,0 +1,11 @@
+{
+  pkgs ? import <nixpkgs> { },
+}:
+pkgs.mkShell {
+  nativeBuildInputs = with pkgs; [
+    cmake
+    qt6.qtbase
+    qt6.wrapQtAppsHook
+    wlr-randr
+  ];
+}

test/screen-uaf-reproducer/trigger.sh

@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+# Trigger rapid output power-cycling to provoke the Qt Wayland screen UAF.
+# Run the reproducer binary first, then this script in another terminal.
+#
+# Usage: ./trigger.sh [iterations]
+#   iterations: number of off/on cycles (default 20)
+
+set -euo pipefail
+
+cycles="${1:-20}"
+
+if command -v niri &>/dev/null && niri msg version &>/dev/null; then
+    echo "Detected Niri - using niri msg"
+    for i in $(seq 1 "$cycles"); do
+        echo "cycle $i/$cycles"
+        niri msg action power-off-monitors
+        sleep 0.3
+        niri msg action power-on-monitors
+        sleep 0.5
+    done
+elif command -v wlr-randr &>/dev/null; then
+    output=$(wlr-randr --json 2>/dev/null | python3 -c \
+        "import sys,json; print(next(o['name'] for o in json.load(sys.stdin) if o['enabled']))" 2>/dev/null \
+        || wlr-randr | grep -oP '^\S+' | head -1)
+    if [ -z "$output" ]; then
+        echo "error: could not detect an output via wlr-randr" >&2
+        exit 1
+    fi
+    echo "Detected wlroots compositor - toggling output $output"
+    for i in $(seq 1 "$cycles"); do
+        echo "cycle $i/$cycles"
+        wlr-randr --output "$output" --off
+        sleep 0.3
+        wlr-randr --output "$output" --on
+        sleep 0.5
+    done
+else
+    echo "error: neither niri nor wlr-randr found" >&2
+    echo "Manually unplug/replug a monitor while the reproducer is running." >&2
+    exit 1
+fi
+
+echo "Done. If the reproducer is still alive, the bug did not trigger."
+echo "Try increasing iterations or adding more surfaces."