Don't crash if the cursor theme fails to create

Summary:
If the cursor theme failed to create KWin crashed due to an endless
recursion. There are two reasons for this fault:
1) When the physical size does not exist we perform a division by 0
which results in an invalid size going into wl_cursor_theme_load
2) We emit the signal that the cursor theme changed even if it didn't
change thus creating an endless recursion

This change addresses both problems: it checks that the size is not 0
and changes the handling for theme update to only destroy the previous
theme if the new theme could be created and only emits the signal if
things change.

BUG: 390314
FIXED-IN: 5.12.3

Test Plan: Added a new test case which crashed with old code

Reviewers: #kwin, #plasma

Subscribers: plasma-devel, kwin

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D10549

autotests/integration/CMakeLists.txt

@@ -55,6 +55,7 @@ integrationTest(WAYLAND_ONLY NAME testVirtualDesktop SRCS virtual_desktop_test.c
 integrationTest(WAYLAND_ONLY NAME testShellClientRules SRCS shell_client_rules_test.cpp)
 integrationTest(WAYLAND_ONLY NAME testIdleInhibition SRCS idle_inhibition_test.cpp)
 integrationTest(WAYLAND_ONLY NAME testColorCorrectNightColor SRCS colorcorrect_nightcolor_test.cpp)
+integrationTest(WAYLAND_ONLY NAME testDontCrashCursorPhysicalSizeEmpty SRCS dont_crash_cursor_physical_size_empty.cpp)
 
 if (XCB_ICCCM_FOUND)
     integrationTest(NAME testMoveResize SRCS move_resize_window_test.cpp LIBS XCB::ICCCM)

autotests/integration/dont_crash_cursor_physical_size_empty.cpp

@@ -0,0 +1,124 @@
+/********************************************************************
+KWin - the KDE window manager
+This file is part of the KDE project.
+
+Copyright (C) 2018 Martin Flöser <mgraesslin@kde.org>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*********************************************************************/
+#include "kwin_wayland_test.h"
+#include "composite.h"
+#include "effectloader.h"
+#include "client.h"
+#include "cursor.h"
+#include "effects.h"
+#include "platform.h"
+#include "shell_client.h"
+#include "screens.h"
+#include "wayland_server.h"
+#include "workspace.h"
+
+#include <KConfigGroup>
+
+#include <KWayland/Client/seat.h>
+#include <KWayland/Client/server_decoration.h>
+#include <KWayland/Client/xdgshell.h>
+#include <KWayland/Client/surface.h>
+#include <KWayland/Server/display.h>
+#include <KWayland/Server/output_interface.h>
+
+using namespace KWin;
+using namespace KWayland::Client;
+static const QString s_socketName = QStringLiteral("wayland_test_kwin_crash_cursor_physical_size_empty-0");
+
+class DontCrashCursorPhysicalSizeEmpty : public QObject
+{
+Q_OBJECT
+private Q_SLOTS:
+    void init();
+    void initTestCase();
+    void cleanup();
+    void testMoveCursorOverDeco_data();
+    void testMoveCursorOverDeco();
+};
+
+void DontCrashCursorPhysicalSizeEmpty::init()
+{
+    QVERIFY(Test::setupWaylandConnection(Test::AdditionalWaylandInterface::Decoration));
+
+    screens()->setCurrent(0);
+    KWin::Cursor::setPos(QPoint(640, 512));
+}
+
+void DontCrashCursorPhysicalSizeEmpty::cleanup()
+{
+    Test::destroyWaylandConnection();
+}
+
+void DontCrashCursorPhysicalSizeEmpty::initTestCase()
+{
+    qRegisterMetaType<KWin::ShellClient*>();
+    qRegisterMetaType<KWin::AbstractClient*>();
+    QSignalSpy workspaceCreatedSpy(kwinApp(), &Application::workspaceCreated);
+    QVERIFY(workspaceCreatedSpy.isValid());
+    kwinApp()->platform()->setInitialWindowSize(QSize(1280, 1024));
+    QVERIFY(waylandServer()->init(s_socketName.toLocal8Bit()));
+
+    if (!QStandardPaths::locateAll(QStandardPaths::GenericDataLocation, QStringLiteral("icons/DMZ-White/index.theme")).isEmpty()) {
+        qputenv("XCURSOR_THEME", QByteArrayLiteral("DMZ-White"));
+    } else {
+        // might be vanilla-dmz (e.g. Arch, FreeBSD)
+        qputenv("XCURSOR_THEME", QByteArrayLiteral("Vanilla-DMZ"));
+    }
+    qputenv("XCURSOR_SIZE", QByteArrayLiteral("0"));
+
+    kwinApp()->start();
+    QVERIFY(workspaceCreatedSpy.wait());
+}
+
+void DontCrashCursorPhysicalSizeEmpty::testMoveCursorOverDeco_data()
+{
+    QTest::addColumn<Test::ShellSurfaceType>("type");
+
+    QTest::newRow("wlShell") << Test::ShellSurfaceType::WlShell;
+    QTest::newRow("xdgShellV5") << Test::ShellSurfaceType::XdgShellV5;
+    QTest::newRow("xdgShellV6") << Test::ShellSurfaceType::XdgShellV6;
+}
+
+void DontCrashCursorPhysicalSizeEmpty::testMoveCursorOverDeco()
+{
+    // This test ensures that there is no endless recursion if the cursor theme cannot be created
+    // a reason for creation failure could be physical size not existing
+    // see BUG: 390314
+    QScopedPointer<Surface> surface(Test::createSurface());
+    QFETCH(Test::ShellSurfaceType, type);
+    Test::waylandServerSideDecoration()->create(surface.data(), surface.data());
+    QScopedPointer<QObject> shellSurface(Test::createShellSurface(type, surface.data()));
+
+    auto c = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
+    QVERIFY(c);
+    QVERIFY(c->isDecorated());
+
+    // destroy physical size
+    KWayland::Server::Display *display = waylandServer()->display();
+    auto output = display->outputs().first();
+    output->setPhysicalSize(QSize(0, 0));
+    // and fake a cursor theme change, so that the theme gets recreated
+    emit KWin::Cursor::self()->themeChanged();
+
+    KWin::Cursor::setPos(QPoint(c->geometry().center().x(), c->clientPos().y() / 2));
+}
+
+WAYLANDTEST_MAIN(DontCrashCursorPhysicalSizeEmpty)
+#include "dont_crash_cursor_physical_size_empty.moc"

wayland_cursor_theme.cpp

@@ -50,12 +50,6 @@ void WaylandCursorTheme::loadTheme()
         return;
     }
     Cursor *c = Cursor::self();
-    if (!m_theme) {
-        // so far the theme had not been created, this means we need to start tracking theme changes
-        connect(c, &Cursor::themeChanged, this, &WaylandCursorTheme::loadTheme);
-    } else {
-        destroyTheme();
-    }
     int size = c->themeSize();
     if (size == 0) {
         // resolution depended
@@ -63,11 +57,25 @@ void WaylandCursorTheme::loadTheme()
         KWayland::Server::Display *display = waylandServer()->display();
         auto output = display->outputs().first();
         // calculate dots per inch, multiplied with magic constants from Cursor::loadThemeSettings()
-        size = qreal(output->pixelSize().height()) / (qreal(output->physicalSize().height()) * 0.0393701) * 16.0 / 72.0;
+        if (output->physicalSize().height()) {
+            size = qreal(output->pixelSize().height()) / (qreal(output->physicalSize().height()) * 0.0393701) * 16.0 / 72.0;
+        } else {
+            // use sensible default
+            size = 24;
+        }
     }
-    m_theme = wl_cursor_theme_load(c->themeName().toUtf8().constData(),
+    auto theme = wl_cursor_theme_load(c->themeName().toUtf8().constData(),
                                    size, m_shm->shm());
-    emit themeChanged();
+    if (theme) {
+        if (!m_theme) {
+            // so far the theme had not been created, this means we need to start tracking theme changes
+            connect(c, &Cursor::themeChanged, this, &WaylandCursorTheme::loadTheme);
+        } else {
+            destroyTheme();
+        }
+        m_theme = theme;
+        emit themeChanged();
+    }
 }
 
 void WaylandCursorTheme::destroyTheme()