Fix crash on serializing default-constructed QTimeZone

The serialization code neglected to check against null.  Since 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)
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

2 files changed, 39 insertions, 3 deletions

diff --git a/src/corelib/time/qtimezone.cpp b/src/corelib/time/qtimezone.cpp
index 6720ede9ed..c3e8947bdc 100644
--- a/src/corelib/time/qtimezone.cpp
+++ b/src/corelib/time/qtimezone.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2013 John Layt <jlayt@kde.org>
+** Copyright (C) 2020 John Layt <jlayt@kde.org>
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -975,9 +975,15 @@ 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;
 }
 
@@ -985,7 +991,9 @@ 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/time/qtimezone/tst_qtimezone.cpp b/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp
index 412f092377..59b94179f4 100644
--- a/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp
+++ b/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp
@@ -65,6 +65,7 @@ private slots:
     void isValidId_data();
     void isValidId();
     void malformed();
+    void serialize();
     // Backend tests
     void utcTest();
     void icuTest();
@@ -951,6 +952,33 @@ void tst_QTimeZone::malformed()
         barf.offsetFromUtc(now);
 }
 
+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