From e325bd68fd6bdcbcb0c4e7478cb6371b60d89905 Mon Sep 17 00:00:00 2001
From: Edward Welbourne <edward.welbourne@qt.io>
Date: Thu, 23 Apr 2020 16:03:59 +0200
Subject: [PATCH] Catch overflow in QDateTime::fromSecsSinceEpoch()

It's documented to be undefined if the number of seconds is outside
the allowed range, but it doesn't hurt for that undefined behavior to
happen to be that the result is invalid. Added a simple test.

Change-Id: I20c3f680c7948b3904f213452272133be77e4d62
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/time/qdatetime.cpp                |  8 +++++
 .../corelib/time/qdatetime/tst_qdatetime.cpp  | 31 +++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/src/corelib/time/qdatetime.cpp b/src/corelib/time/qdatetime.cpp
index 2e4757b525..248fd1d5ce 100644
--- a/src/corelib/time/qdatetime.cpp
+++ b/src/corelib/time/qdatetime.cpp
@@ -4608,6 +4608,10 @@ QDateTime QDateTime::fromMSecsSinceEpoch(qint64 msecs, Qt::TimeSpec spec, int of
 */
 QDateTime QDateTime::fromSecsSinceEpoch(qint64 secs, Qt::TimeSpec spec, int offsetSeconds)
 {
+    constexpr qint64 maxSeconds = std::numeric_limits<qint64>::max() / 1000;
+    constexpr qint64 minSeconds = std::numeric_limits<qint64>::min() / 1000;
+    if (secs > maxSeconds || secs < minSeconds)
+        return QDateTime(); // Would {und,ov}erflow
     return fromMSecsSinceEpoch(secs * 1000, spec, offsetSeconds);
 }
 
@@ -4641,6 +4645,10 @@ QDateTime QDateTime::fromMSecsSinceEpoch(qint64 msecs, const QTimeZone &timeZone
 */
 QDateTime QDateTime::fromSecsSinceEpoch(qint64 secs, const QTimeZone &timeZone)
 {
+    constexpr qint64 maxSeconds = std::numeric_limits<qint64>::max() / 1000;
+    constexpr qint64 minSeconds = std::numeric_limits<qint64>::min() / 1000;
+    if (secs > maxSeconds || secs < minSeconds)
+        return QDateTime(); // Would {und,ov}erflow
     return fromMSecsSinceEpoch(secs * 1000, timeZone);
 }
 #endif
diff --git a/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp b/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
index 2e45460544..bf84508522 100644
--- a/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
+++ b/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
@@ -73,6 +73,7 @@ private slots:
     void setSecsSinceEpoch();
     void setMSecsSinceEpoch_data();
     void setMSecsSinceEpoch();
+    void fromSecsSinceEpoch();
     void fromMSecsSinceEpoch_data();
     void fromMSecsSinceEpoch();
     void toString_isoDate_data();
@@ -790,6 +791,36 @@ void tst_QDateTime::fromMSecsSinceEpoch()
     QCOMPARE(dtOffset, reference.addMSecs(msecs));
 }
 
+void tst_QDateTime::fromSecsSinceEpoch()
+{
+    const qint64 maxSeconds = std::numeric_limits<qint64>::max() / 1000;
+
+    QVERIFY(QDateTime::fromSecsSinceEpoch(maxSeconds).isValid());
+    QVERIFY(!QDateTime::fromSecsSinceEpoch(maxSeconds + 1).isValid());
+    QVERIFY(QDateTime::fromSecsSinceEpoch(-maxSeconds).isValid());
+    QVERIFY(!QDateTime::fromSecsSinceEpoch(-maxSeconds - 1).isValid());
+
+    QVERIFY(QDateTime::fromSecsSinceEpoch(maxSeconds, Qt::UTC).isValid());
+    QVERIFY(!QDateTime::fromSecsSinceEpoch(maxSeconds + 1, Qt::UTC).isValid());
+    QVERIFY(QDateTime::fromSecsSinceEpoch(-maxSeconds, Qt::UTC).isValid());
+    QVERIFY(!QDateTime::fromSecsSinceEpoch(-maxSeconds - 1, Qt::UTC).isValid());
+
+    // Use an offset for which .toUTC()'s return would flip the validity:
+    QVERIFY(QDateTime::fromSecsSinceEpoch(maxSeconds, Qt::OffsetFromUTC, 7200).isValid());
+    QVERIFY(!QDateTime::fromSecsSinceEpoch(maxSeconds + 1, Qt::OffsetFromUTC, -7200).isValid());
+    QVERIFY(QDateTime::fromSecsSinceEpoch(-maxSeconds, Qt::OffsetFromUTC, -7200).isValid());
+    QVERIFY(!QDateTime::fromSecsSinceEpoch(-maxSeconds - 1, Qt::OffsetFromUTC, 7200).isValid());
+
+#if QT_CONFIG(timezone)
+    // As for offset, use zones each side of UTC:
+    const QTimeZone west("UTC-02:00"), east("UTC+02:00");
+    QVERIFY(QDateTime::fromSecsSinceEpoch(maxSeconds, east).isValid());
+    QVERIFY(!QDateTime::fromSecsSinceEpoch(maxSeconds + 1, west).isValid());
+    QVERIFY(QDateTime::fromSecsSinceEpoch(-maxSeconds, west).isValid());
+    QVERIFY(!QDateTime::fromSecsSinceEpoch(-maxSeconds - 1, east).isValid());
+#endif // timezone
+}
+
 void tst_QDateTime::toString_isoDate_data()
 {
     QTest::addColumn<QDateTime>("datetime");