QInputDialog: prevent crash in static get*() functions when parent gets deleted

As explained in

   https://blogs.kde.org/2009/03/26/how-crash-almost-every-qtkde-application-and-how-fix-it-0

creating dialogs on the stack is a bad idea if the
application or the dialog's parent window can be closed
by means other than user interaction (such as a timer or
an IPC call). Since we cannot know whether Qt is used to
build such an application, we must assume it is, create
the dialog on the heap, and monitor its lifetime with a
QPointer.

Instead of using manual resource management, add a
minimal implementation of QAutoPointer, and use that in
all static get*() functions.

Task-number: QTBUG-54693
Change-Id: I6157dca18608e02be1ea2c2defbc31641defc9d1
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: David Faure <david.faure@kdab.com>

src/widgets/dialogs/qdialog_p.h

@@ -119,6 +119,24 @@ private:
     mutable bool m_platformHelperCreated;
 };
 
+template <typename T>
+class QAutoPointer {
+    QPointer<T> o;
+    struct internal { void func() {} };
+    typedef void (internal::*RestrictedBool)();
+public:
+    explicit QAutoPointer(T *t) Q_DECL_NOTHROW : o(t) {}
+    ~QAutoPointer() { delete o; }
+
+    T *operator->() const Q_DECL_NOTHROW { return get(); }
+    T *get() const Q_DECL_NOTHROW { return o; }
+    T &operator*() const { return *get(); }
+    operator RestrictedBool() const Q_DECL_NOTHROW { return o ? &internal::func : Q_NULLPTR; }
+    bool operator!() const Q_DECL_NOTHROW { return !o; }
+private:
+    Q_DISABLE_COPY(QAutoPointer);
+};
+
 QT_END_NAMESPACE
 
 #endif // QDIALOG_P_H

src/widgets/dialogs/qinputdialog.cpp

@@ -1194,10 +1194,6 @@ void QInputDialog::done(int result)
 
     \snippet dialogs/standarddialogs/dialog.cpp 3
 
-    \warning Do not delete \a parent during the execution of the dialog. If you
-    want to do this, you should create the dialog yourself using one of the
-    QInputDialog constructors.
-
     \sa getInt(), getDouble(), getItem(), getMultiLineText()
 */
 
@@ -1205,18 +1201,18 @@ QString QInputDialog::getText(QWidget *parent, const QString &title, const QStri
                               QLineEdit::EchoMode mode, const QString &text, bool *ok,
                               Qt::WindowFlags flags, Qt::InputMethodHints inputMethodHints)
 {
-    QInputDialog dialog(parent, flags);
+    QAutoPointer<QInputDialog> dialog(new QInputDialog(parent, flags));
-    dialog.setWindowTitle(title);
+    dialog->setWindowTitle(title);
-    dialog.setLabelText(label);
+    dialog->setLabelText(label);
-    dialog.setTextValue(text);
+    dialog->setTextValue(text);
-    dialog.setTextEchoMode(mode);
+    dialog->setTextEchoMode(mode);
-    dialog.setInputMethodHints(inputMethodHints);
+    dialog->setInputMethodHints(inputMethodHints);
 
-    int ret = dialog.exec();
+    const int ret = dialog->exec();
     if (ok)
         *ok = !!ret;
     if (ret) {
-        return dialog.textValue();
+        return dialog->textValue();
     } else {
         return QString();
     }
@@ -1246,10 +1242,6 @@ QString QInputDialog::getText(QWidget *parent, const QString &title, const QStri
 
     \snippet dialogs/standarddialogs/dialog.cpp 4
 
-    \warning Do not delete \a parent during the execution of the dialog. If you
-    want to do this, you should create the dialog yourself using one of the
-    QInputDialog constructors.
-
     \sa getInt(), getDouble(), getItem(), getText()
 */
 
@@ -1257,18 +1249,18 @@ QString QInputDialog::getMultiLineText(QWidget *parent, const QString &title, co
                                        const QString &text, bool *ok, Qt::WindowFlags flags,
                                        Qt::InputMethodHints inputMethodHints)
 {
-    QInputDialog dialog(parent, flags);
+    QAutoPointer<QInputDialog> dialog(new QInputDialog(parent, flags));
-    dialog.setOptions(QInputDialog::UsePlainTextEditForTextInput);
+    dialog->setOptions(QInputDialog::UsePlainTextEditForTextInput);
-    dialog.setWindowTitle(title);
+    dialog->setWindowTitle(title);
-    dialog.setLabelText(label);
+    dialog->setLabelText(label);
-    dialog.setTextValue(text);
+    dialog->setTextValue(text);
-    dialog.setInputMethodHints(inputMethodHints);
+    dialog->setInputMethodHints(inputMethodHints);
 
-    int ret = dialog.exec();
+    const int ret = dialog->exec();
     if (ok)
         *ok = !!ret;
     if (ret) {
-        return dialog.textValue();
+        return dialog->textValue();
     } else {
         return QString();
     }
@@ -1298,28 +1290,24 @@ QString QInputDialog::getMultiLineText(QWidget *parent, const QString &title, co
 
     \snippet dialogs/standarddialogs/dialog.cpp 0
 
-    \warning Do not delete \a parent during the execution of the dialog. If you
-    want to do this, you should create the dialog yourself using one of the
-    QInputDialog constructors.
-
     \sa getText(), getDouble(), getItem(), getMultiLineText()
 */
 
 int QInputDialog::getInt(QWidget *parent, const QString &title, const QString &label, int value,
                          int min, int max, int step, bool *ok, Qt::WindowFlags flags)
 {
-    QInputDialog dialog(parent, flags);
+    QAutoPointer<QInputDialog> dialog(new QInputDialog(parent, flags));
-    dialog.setWindowTitle(title);
+    dialog->setWindowTitle(title);
-    dialog.setLabelText(label);
+    dialog->setLabelText(label);
-    dialog.setIntRange(min, max);
+    dialog->setIntRange(min, max);
-    dialog.setIntValue(value);
+    dialog->setIntValue(value);
-    dialog.setIntStep(step);
+    dialog->setIntStep(step);
 
-    int ret = dialog.exec();
+    const int ret = dialog->exec();
     if (ok)
         *ok = !!ret;
     if (ret) {
-        return dialog.intValue();
+        return dialog->intValue();
     } else {
         return value;
     }
@@ -1350,10 +1338,6 @@ int QInputDialog::getInt(QWidget *parent, const QString &title, const QString &l
 
     \snippet dialogs/standarddialogs/dialog.cpp 0
 
-    \warning Do not delete \a parent during the execution of the dialog. If you
-    want to do this, you should create the dialog yourself using one of the
-    QInputDialog constructors.
-
     \sa getText(), getDouble(), getItem(), getMultiLineText()
 */
 
@@ -1379,10 +1363,6 @@ int QInputDialog::getInt(QWidget *parent, const QString &title, const QString &l
 
     \snippet dialogs/standarddialogs/dialog.cpp 1
 
-    \warning Do not delete \a parent during the execution of the dialog. If you
-    want to do this, you should create the dialog yourself using one of the
-    QInputDialog constructors.
-
     \sa getText(), getInt(), getItem(), getMultiLineText()
 */
 
@@ -1390,18 +1370,18 @@ double QInputDialog::getDouble(QWidget *parent, const QString &title, const QStr
                                double value, double min, double max, int decimals, bool *ok,
                                Qt::WindowFlags flags)
 {
-    QInputDialog dialog(parent, flags);
+    QAutoPointer<QInputDialog> dialog(new QInputDialog(parent, flags));
-    dialog.setWindowTitle(title);
+    dialog->setWindowTitle(title);
-    dialog.setLabelText(label);
+    dialog->setLabelText(label);
-    dialog.setDoubleDecimals(decimals);
+    dialog->setDoubleDecimals(decimals);
-    dialog.setDoubleRange(min, max);
+    dialog->setDoubleRange(min, max);
-    dialog.setDoubleValue(value);
+    dialog->setDoubleValue(value);
 
-    int ret = dialog.exec();
+    const int ret = dialog->exec();
     if (ok)
         *ok = !!ret;
     if (ret) {
-        return dialog.doubleValue();
+        return dialog->doubleValue();
     } else {
         return value;
     }
@@ -1433,10 +1413,6 @@ double QInputDialog::getDouble(QWidget *parent, const QString &title, const QStr
 
     \snippet dialogs/standarddialogs/dialog.cpp 2
 
-    \warning Do not delete \a parent during the execution of the dialog. If you
-    want to do this, you should create the dialog yourself using one of the
-    QInputDialog constructors.
-
     \sa getText(), getInt(), getDouble(), getMultiLineText()
 */
 
@@ -1446,19 +1422,19 @@ QString QInputDialog::getItem(QWidget *parent, const QString &title, const QStri
 {
     QString text(items.value(current));
 
-    QInputDialog dialog(parent, flags);
+    QAutoPointer<QInputDialog> dialog(new QInputDialog(parent, flags));
-    dialog.setWindowTitle(title);
+    dialog->setWindowTitle(title);
-    dialog.setLabelText(label);
+    dialog->setLabelText(label);
-    dialog.setComboBoxItems(items);
+    dialog->setComboBoxItems(items);
-    dialog.setTextValue(text);
+    dialog->setTextValue(text);
-    dialog.setComboBoxEditable(editable);
+    dialog->setComboBoxEditable(editable);
-    dialog.setInputMethodHints(inputMethodHints);
+    dialog->setInputMethodHints(inputMethodHints);
 
-    int ret = dialog.exec();
+    const int ret = dialog->exec();
     if (ok)
         *ok = !!ret;
     if (ret) {
-        return dialog.textValue();
+        return dialog->textValue();
     } else {
         return text;
     }

tests/auto/widgets/dialogs/qinputdialog/qinputdialog.pro

@@ -1,4 +1,4 @@
 CONFIG += testcase
 TARGET = tst_qinputdialog
-QT += widgets testlib
+QT += widgets-private testlib
 SOURCES  += tst_qinputdialog.cpp

tests/auto/widgets/dialogs/qinputdialog/tst_qinputdialog.cpp

@@ -35,6 +35,7 @@
 #include <QComboBox>
 #include <QDialogButtonBox>
 #include <qinputdialog.h>
+#include <QtWidgets/private/qdialog_p.h>
 
 class tst_QInputDialog : public QObject
 {
@@ -52,6 +53,7 @@ private slots:
     void getInt();
     void getDouble_data();
     void getDouble();
+    void taskQTBUG_54693_crashWhenParentIsDeletedWhileDialogIsOpen();
     void task255502getDouble();
     void getText_data();
     void getText();
@@ -311,6 +313,75 @@ void tst_QInputDialog::getDouble()
     delete parent;
 }
 
+namespace {
+class SelfDestructParent : public QWidget
+{
+    Q_OBJECT
+public:
+    explicit SelfDestructParent(int delay = 100)
+        : QWidget(Q_NULLPTR)
+    {
+        QTimer::singleShot(delay, this, SLOT(deleteLater()));
+    }
+};
+}
+
+void tst_QInputDialog::taskQTBUG_54693_crashWhenParentIsDeletedWhileDialogIsOpen()
+{
+    // getText
+    {
+        QAutoPointer<SelfDestructParent> dialog(new SelfDestructParent);
+        bool ok = true;
+        const QString result = QInputDialog::getText(dialog.get(), "Title", "Label", QLineEdit::Normal, "Text", &ok);
+        QVERIFY(!dialog);
+        QVERIFY(!ok);
+        QVERIFY(result.isNull());
+    }
+
+    // getMultiLineText
+    {
+        QAutoPointer<SelfDestructParent> dialog(new SelfDestructParent);
+        bool ok = true;
+        const QString result = QInputDialog::getMultiLineText(dialog.get(), "Title", "Label", "Text", &ok);
+        QVERIFY(!dialog);
+        QVERIFY(!ok);
+        QVERIFY(result.isNull());
+    }
+
+    // getItem
+    for (int editable = false; editable <= true; ++editable) {
+        QAutoPointer<SelfDestructParent> dialog(new SelfDestructParent);
+        bool ok = true;
+        const QString result = QInputDialog::getItem(dialog.get(), "Title", "Label",
+                                                     QStringList() << "1" << "2", 1, editable, &ok);
+        QVERIFY(!dialog);
+        QVERIFY(!ok);
+        QCOMPARE(result, QLatin1String("2"));
+    }
+
+    // getInt
+    {
+        const int initial = 7;
+        QAutoPointer<SelfDestructParent> dialog(new SelfDestructParent);
+        bool ok = true;
+        const int result = QInputDialog::getInt(dialog.get(), "Title", "Label", initial, -10, +10, 1, &ok);
+        QVERIFY(!dialog);
+        QVERIFY(!ok);
+        QCOMPARE(result, initial);
+    }
+
+    // getDouble
+    {
+        const double initial = 7;
+        QAutoPointer<SelfDestructParent> dialog(new SelfDestructParent);
+        bool ok = true;
+        const double result = QInputDialog::getDouble(dialog.get(), "Title", "Label", initial, -10, +10, 2, &ok);
+        QVERIFY(!dialog);
+        QVERIFY(!ok);
+        QCOMPARE(result, initial);
+    }
+}
+
 void tst_QInputDialog::task255502getDouble()
 {
     parent = new QWidget;