Fix crash on serializing default-constructed QTimeZone

The serialization code neglected to check against null.  Sinze zones
are saved either by IANA ID or in our special OffsetFromUtc format,
representing an invalid zone by a string that cannot possibly be a
valid IANA ID will do.

Fixes: QTBUG-86019
Change-Id: I6882026403d00f8b254aab34c645f1cf8f9fcc2d
Reviewed-by: Taylor Braun-Jones <taylor@braun-jones.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 14f3f419b0864944d75283a850dc0ce141feaf0e)

2 files changed, 40 insertions, 3 deletions

diff --git a/src/corelib/tools/qtimezone.cpp b/src/corelib/tools/qtimezone.cpp
index cbc6b50c98..e0ce5dcd0d 100644
--- a/src/corelib/tools/qtimezone.cpp
+++ b/src/corelib/tools/qtimezone.cpp
@@ -1,5 +1,6 @@
 /****************************************************************************
 **
+** Copyright (C) 2020 The Qt Company Ltd.
 ** Copyright (C) 2013 John Layt <jlayt@kde.org>
 ** Contact: https://www.qt.io/licensing/
 **
@@ -953,9 +954,15 @@ QList<QByteArray> QTimeZone::windowsIdToIanaIds(const QByteArray &windowsId,
 }
 
 #ifndef QT_NO_DATASTREAM
+// Invalid, as an IANA ID: too long, starts with - and has other invalid characters in it
+static inline QString invalidId() { return QStringLiteral("-No Time Zone Specified!"); }
+
 QDataStream &operator<<(QDataStream &ds, const QTimeZone &tz)
 {
-    tz.d->serialize(ds);
+    if (tz.isValid())
+        tz.d->serialize(ds);
+    else
+        ds << invalidId();
     return ds;
 }
 
@@ -963,7 +970,9 @@ QDataStream &operator>>(QDataStream &ds, QTimeZone &tz)
 {
     QString ianaId;
     ds >> ianaId;
-    if (ianaId == QLatin1String("OffsetFromUtc")) {
+    if (ianaId == invalidId()) {
+        tz = QTimeZone();
+    } else if (ianaId == QLatin1String("OffsetFromUtc")) {
         int utcOffset;
         QString name;
         QString abbreviation;
diff --git a/tests/auto/corelib/tools/qtimezone/tst_qtimezone.cpp b/tests/auto/corelib/tools/qtimezone/tst_qtimezone.cpp
index bb6c48a2ed..1421aa2760 100644
--- a/tests/auto/corelib/tools/qtimezone/tst_qtimezone.cpp
+++ b/tests/auto/corelib/tools/qtimezone/tst_qtimezone.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2020 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the test suite of the Qt Toolkit.
@@ -59,6 +59,7 @@ private slots:
     void windowsId();
     void isValidId_data();
     void isValidId();
+    void serialize();
     // Backend tests
     void utcTest();
     void icuTest();
@@ -782,6 +783,33 @@ void tst_QTimeZone::isValidId()
 #endif
 }
 
+void tst_QTimeZone::serialize()
+{
+    int parts = 0;
+#ifndef QT_NO_DEBUG_STREAM
+    qDebug() << QTimeZone(); // to verify no crash
+    parts++;
+#endif
+#ifndef QT_NO_DATASTREAM
+    QByteArray blob;
+    {
+        QDataStream stream(&blob, QIODevice::WriteOnly);
+        stream << QTimeZone("Europe/Oslo") << QTimeZone(420) << QTimeZone() << qint64(-1);
+    }
+    QDataStream stream(&blob, QIODevice::ReadOnly);
+    QTimeZone invalid, offset, oslo;
+    qint64 minusone;
+    stream >> oslo >> offset >> invalid >> minusone;
+    QCOMPARE(oslo, QTimeZone("Europe/Oslo"));
+    QCOMPARE(offset, QTimeZone(420));
+    QVERIFY(!invalid.isValid());
+    QCOMPARE(minusone, qint64(-1));
+    parts++;
+#endif
+    if (!parts)
+        QSKIP("No serialization enabled");
+}
+
 void tst_QTimeZone::utcTest()
 {
 #ifdef QT_BUILD_INTERNAL