WindowServer: Normalize preferred rect before applying

Previously, SetWindowRect and SetWindowRect could supply basically arbitrary
x and y coordinates. This could happen either due to a malicious or malfunctioning
program, or even due to the auto-centering feature.

This patch also moves the 'normalization' code out of ClientConnection to Window,
where it belongs better.

Fixes #4135.
Fixes #5052.

Userland/Services/WindowServer/ClientConnection.cpp

@@ -48,15 +48,6 @@ namespace WindowServer {
 
 HashMap<int, NonnullRefPtr<ClientConnection>>* s_connections;
 
-static Gfx::IntRect normalize_window_rect(Gfx::IntRect rect, WindowType window_type)
-{
-    auto min_size = 1;
-    if (window_type == WindowType::Normal)
-        min_size = 50;
-    Gfx::IntRect normalized_rect = { rect.x(), rect.y(), max(rect.width(), min_size), max(rect.height(), min_size) };
-    return normalized_rect;
-}
-
 void ClientConnection::for_each_client(Function<void(ClientConnection&)> callback)
 {
     if (!s_connections)
@@ -403,10 +394,10 @@ OwnPtr<Messages::WindowServer::SetWindowRectResponse> ClientConnection::handle(c
     if (message.rect().location() != window.rect().location()) {
         window.set_default_positioned(false);
     }
-    auto normalized_rect = normalize_window_rect(message.rect(), window.type());
+    window.set_rect(message.rect());
-    window.set_rect(normalized_rect);
+    window.normalize_rect();
-    window.request_update(normalized_rect);
+    window.request_update(window.rect());
-    return make<Messages::WindowServer::SetWindowRectResponse>(normalized_rect);
+    return make<Messages::WindowServer::SetWindowRectResponse>(window.rect());
 }
 
 OwnPtr<Messages::WindowServer::GetWindowRectResponse> ClientConnection::handle(const Messages::WindowServer::GetWindowRect& message)
@@ -461,8 +452,8 @@ OwnPtr<Messages::WindowServer::CreateWindowResponse> ClientConnection::handle(co
             rect = { WindowManager::the().get_recommended_window_position({ 100, 100 }), message.rect().size() };
             window->set_default_positioned(true);
         }
-        auto normalized_rect = normalize_window_rect(rect, window->type());
+        window->set_rect(rect);
-        window->set_rect(normalized_rect);
+        window->normalize_rect();
     }
     if (window->type() == WindowType::Desktop) {
         window->set_rect(WindowManager::the().desktop_rect());

Userland/Services/WindowServer/Window.cpp

@@ -176,6 +176,32 @@ void Window::set_rect_without_repaint(const Gfx::IntRect& rect)
     m_frame.notify_window_rect_changed(old_rect, rect); // recomputes occlusions
 }
 
+void Window::normalize_rect()
+{
+    auto min_size = 1;
+    // Must be -1 to allow windows just outside the desktop rect.
+    // For example, the windows that make the desktop rect smaller
+    // than the display resolution (e.g. the TaskBar).
+    auto min_visible = -1;
+    auto desktop = WindowManager::the().desktop_rect();
+    auto min_y = 0;
+    if (type() == WindowType::Normal) {
+        min_size = 50;
+        min_visible = 50;
+        // 5 pixels is the amount of frame decoration that can be sacrificed before starting to become an issue.
+        min_y = desktop.top() - 5;
+    }
+    auto new_width = max(width(), min_size);
+    auto new_height = max(height(), min_size);
+    Gfx::IntRect normalized_rect = {
+        clamp(x(), -new_width + min_visible, desktop.width() - min_visible),
+        clamp(y(), min_y, desktop.bottom() - min_visible),
+        new_width,
+        new_height,
+    };
+    set_rect(normalized_rect);
+}
+
 void Window::handle_mouse_event(const MouseEvent& event)
 {
     set_automatic_cursor_tracking_enabled(event.buttons() != 0);

Userland/Services/WindowServer/Window.h

@@ -158,6 +158,7 @@ public:
     void set_rect(const Gfx::IntRect&);
     void set_rect(int x, int y, int width, int height) { set_rect({ x, y, width, height }); }
     void set_rect_without_repaint(const Gfx::IntRect&);
+    void normalize_rect();
 
     void set_taskbar_rect(const Gfx::IntRect&);
     const Gfx::IntRect& taskbar_rect() const { return m_taskbar_rect; }