Fix undo and redo in QLineEdit when in password mode

There are some security issues with undo/redo. User should not be
able to get the erased password back in any situation. Therefore
redo must be disabled completely and undo is limited only for erasing
previously entered text.

Task-number: QTBUG-14226
Change-Id: I2b38aca84adbad1c14db76b56ad6303d56b35b4d
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>

src/widgets/widgets/qwidgetlinecontrol.cpp

@@ -1279,6 +1279,13 @@ void QWidgetLineControl::internalUndo(int until)
         return;
     cancelPasswordEchoTimer();
     internalDeselect();
+
+    // Undo works only for clearing the line when in any of password the modes
+    if (m_echoMode != QLineEdit::Normal) {
+        clear();
+        return;
+    }
+
     while (m_undoState && m_undoState > until) {
         Command& cmd = m_history[--m_undoState];
         switch (cmd.type) {
@@ -1868,6 +1875,21 @@ void QWidgetLineControl::processKeyEvent(QKeyEvent* event)
         event->accept();
 }
 
+bool QWidgetLineControl::isUndoAvailable() const
+{
+    // For security reasons undo is not available in any password mode (NoEcho included)
+    // with the exception that the user can clear the password with undo.
+    return !m_readOnly && m_undoState
+            && (m_echoMode == QLineEdit::Normal || m_history[m_undoState - 1].type == QWidgetLineControl::Insert);
+}
+
+bool QWidgetLineControl::isRedoAvailable() const
+{
+    // Same as with undo. Disabled for password modes.
+    return !m_readOnly
+            && m_echoMode == QLineEdit::Normal
+            && m_undoState < m_history.size();
+}
 
 QT_END_NAMESPACE
 

src/widgets/widgets/qwidgetlinecontrol_p.h

@@ -125,8 +125,8 @@ public:
         return (c != -1 ? c : 0);
     }
 
-    bool isUndoAvailable() const { return !m_readOnly && m_undoState; }
-    bool isRedoAvailable() const { return !m_readOnly && m_undoState < (int)m_history.size(); }
+    bool isUndoAvailable() const;
+    bool isRedoAvailable() const;
     void clearUndo() { m_history.clear(); m_modifiedState = m_undoState = 0; }
 
     bool isModified() const { return m_modifiedState != m_undoState; }

tests/auto/widgets/widgets/qlineedit/tst_qlineedit.cpp

@@ -287,6 +287,9 @@ private slots:
     void inputMethodQueryImHints_data();
     void inputMethodQueryImHints();
 
+    void undoRedoAndEchoModes_data();
+    void undoRedoAndEchoModes();
+
 protected slots:
     void editingFinished();
 
@@ -3954,5 +3957,68 @@ void tst_QLineEdit::inputMethodQueryImHints()
     QCOMPARE(static_cast<Qt::InputMethodHints>(value.toInt()), hints);
 }
 
+void tst_QLineEdit::undoRedoAndEchoModes_data()
+{
+    QTest::addColumn<int>("echoMode");
+    QTest::addColumn<QStringList>("input");
+    QTest::addColumn<QStringList>("expected");
+
+    QStringList input(QList<QString>() << "aaa" << "bbb" << "ccc");
+
+    QTest::newRow("Normal")
+        << (int) QLineEdit::Normal
+        << input
+        << QStringList(QList<QString>() << "aaa" << "ccc" << "");
+
+    QTest::newRow("NoEcho")
+        << (int) QLineEdit::NoEcho
+        << input
+        << QStringList(QList<QString>() << "" << "" << "");
+
+    QTest::newRow("Password")
+        << (int) QLineEdit::Password
+        << input
+        << QStringList(QList<QString>() << "" << "" << "");
+
+    QTest::newRow("PasswordEchoOnEdit")
+        << (int) QLineEdit::PasswordEchoOnEdit
+        << input
+        << QStringList(QList<QString>() << "" << "" << "");
+}
+
+void tst_QLineEdit::undoRedoAndEchoModes()
+{
+    QFETCH(int, echoMode);
+    QFETCH(QStringList, input);
+    QFETCH(QStringList, expected);
+
+    // create some history for the QLineEdit
+    testWidget->clear();
+    testWidget->setEchoMode(QLineEdit::EchoMode(echoMode));
+    testWidget->insert(input.at(0));
+    testWidget->selectAll();
+    testWidget->backspace();
+    testWidget->insert(input.at(1));
+
+    // test undo
+    QVERIFY(testWidget->isUndoAvailable());
+    testWidget->undo();
+    QCOMPARE(testWidget->text(), expected.at(0));
+    testWidget->insert(input.at(2));
+    testWidget->selectAll();
+    testWidget->backspace();
+    QCOMPARE(testWidget->isUndoAvailable(), echoMode == QLineEdit::Normal);
+    testWidget->undo();
+    QCOMPARE(testWidget->text(), expected.at(1));
+
+    // test redo
+    QCOMPARE(testWidget->isRedoAvailable(), echoMode == QLineEdit::Normal);
+    testWidget->redo();
+    QCOMPARE(testWidget->text(), expected.at(2));
+    QVERIFY(!testWidget->isRedoAvailable());
+    testWidget->redo();
+    QCOMPARE(testWidget->text(), expected.at(2));
+}
+
 QTEST_MAIN(tst_QLineEdit)
 #include "tst_qlineedit.moc"