WindowServer: Make SetWindowTaskbarRect tolerant to non-existing windows

There is a window between windows disappearing (e.g. closing or crashes)
and the Taskbar process being notified. So it is entirely possible that
it may call SetWindowTaskbarRect() for a window and/or client id that no
longer exists. As the Taskbar process does not own these windows, this
should not be treated as a misbehaving application request. Instead, just
silently ignore the request. The Taskbar will be notified shortly after
that the window no longer exist and remove it from its list.

Fixes #3494

1 files changed, 8 insertions, 6 deletions

diff --git a/Services/WindowServer/ClientConnection.cpp b/Services/WindowServer/ClientConnection.cpp
index 6244cdc5ac..cdb7d35a52 100644
--- a/Services/WindowServer/ClientConnection.cpp
+++ b/Services/WindowServer/ClientConnection.cpp
@@ -723,16 +723,18 @@ OwnPtr<Messages::WindowServer::GreetResponse> ClientConnection::handle(const Mes
 
 void ClientConnection::handle(const Messages::WindowServer::WM_SetWindowTaskbarRect& message)
 {
+    // Because the Taskbar (which should be the only user of this API) does not own the
+    // window or the client id, there is a possibility that it may send this message for
+    // a window or client that may have been destroyed already. This is not an error,
+    // and we should not call did_misbehave() for either.
     auto* client = ClientConnection::from_client_id(message.client_id());
-    if (!client) {
-        did_misbehave("WM_SetWindowTaskbarRect: Bad client ID");
+    if (!client)
         return;
-    }
+
     auto it = client->m_windows.find(message.window_id());
-    if (it == client->m_windows.end()) {
-        did_misbehave("WM_SetWindowTaskbarRect: Bad window ID");
+    if (it == client->m_windows.end())
         return;
-    }
+
     auto& window = *(*it).value;
     window.set_taskbar_rect(message.rect());
 }