Fix some out-of-range issues with time-zone support

The MS-Windows back-end neglected to check for overflow when mapping
date and time to milliseconds from the epoch. Add the checks for that
and take care not to return qint64-min as a transition time - that's
the invalidMSecs() value used as a special marker.

QTimeZonePrivate::dataForLocalTime() neglected to handle the case of
the backend being unable to answer offsetFromUtc() for one of the
times requested, which the MS backend might.

Change-Id: I6d7ee2cbf9aaf6678abb24a20e18b5cdac7f5a23
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 24 insertions, 12 deletions

diff --git a/src/corelib/time/qtimezoneprivate.cpp b/src/corelib/time/qtimezoneprivate.cpp
index 6b92d60f7f..c90547d0ee 100644
--- a/src/corelib/time/qtimezoneprivate.cpp
+++ b/src/corelib/time/qtimezoneprivate.cpp
@@ -395,9 +395,12 @@ QTimeZonePrivate::Data QTimeZonePrivate::dataForLocalTime(qint64 forLocalMSecs,
 
     int early = offsetFromUtc(recent);
     int late = offsetFromUtc(imminent);
-    if (early == late) { // > 99% of the time
-        if (sub_overflow(forLocalMSecs, early * qint64(1000), &utcEpochMSecs))
+    if (early == late // > 99% of the time
+        || late == invalidSeconds()) {
+        if (early == invalidSeconds()
+            || sub_overflow(forLocalMSecs, early * qint64(1000), &utcEpochMSecs)) {
             return invalidData(); // Outside representable range
+        }
     } else {
         // Close to a DST transition: early > late is near a fall-back,
         // early < late is near a spring-forward.
diff --git a/src/corelib/time/qtimezoneprivate_win.cpp b/src/corelib/time/qtimezoneprivate_win.cpp
index 2e2f4f423d..890a95c882 100644
--- a/src/corelib/time/qtimezoneprivate_win.cpp
+++ b/src/corelib/time/qtimezoneprivate_win.cpp
@@ -1,5 +1,6 @@
 /****************************************************************************
 **
+** Copyright (C) 2021 The Qt Company Ltd.
 ** Copyright (C) 2013 John Layt <jlayt@kde.org>
 ** Contact: https://www.qt.io/licensing/
 **
@@ -41,8 +42,8 @@
 #include "qtimezoneprivate_p.h"
 
 #include "qdatetime.h"
-
 #include "qdebug.h"
+#include <private/qnumeric_p.h>
 
 #include <algorithm>
 
@@ -95,9 +96,9 @@ namespace {
 QDate msecsToDate(qint64 msecs)
 {
     qint64 jd = JULIAN_DAY_FOR_EPOCH;
-
-    if (qAbs(msecs) >= MSECS_PER_DAY) {
-        jd += (msecs / MSECS_PER_DAY);
+    // Corner case: don't use qAbs() because msecs may be numeric_limits<qint64>::min()
+    if (msecs >= MSECS_PER_DAY || msecs <= -MSECS_PER_DAY) {
+        jd += msecs / MSECS_PER_DAY;
         msecs %= MSECS_PER_DAY;
     }
 
@@ -275,11 +276,12 @@ QDate calculateTransitionLocalDate(const SYSTEMTIME &rule, int year)
     return date;
 }
 
-// Converts a date/time value into msecs
-inline qint64 timeToMSecs(QDate date, QTime time)
+// Converts a date/time value into msecs, returns true on overflow:
+inline bool timeToMSecs(QDate date, QTime time, qint64 *msecs)
 {
-    return ((date.toJulianDay() - JULIAN_DAY_FOR_EPOCH) * MSECS_PER_DAY)
-           + time.msecsSinceStartOfDay();
+    qint64 dayms = 0;
+    return mul_overflow(date.toJulianDay() - JULIAN_DAY_FOR_EPOCH, qint64(MSECS_PER_DAY), &dayms)
+        || add_overflow(dayms, qint64(time.msecsSinceStartOfDay()), msecs);
 }
 
 qint64 calculateTransitionForYear(const SYSTEMTIME &rule, int year, int bias)
@@ -289,8 +291,15 @@ qint64 calculateTransitionForYear(const SYSTEMTIME &rule, int year, int bias)
     Q_ASSERT(year);
     const QDate date = calculateTransitionLocalDate(rule, year);
     const QTime time = QTime(rule.wHour, rule.wMinute, rule.wSecond);
-    if (date.isValid() && time.isValid())
-        return timeToMSecs(date, time) + bias * 60000;
+    qint64 msecs = 0;
+    using Bound = std::numeric_limits<qint64>;
+    if (date.isValid() && time.isValid() && !timeToMSecs(date, time, &msecs)) {
+        // If bias pushes us outside representable range, clip to range - and
+        // exclude min() from range as it's invalidMSecs():
+        return bias && add_overflow(msecs, qint64(bias) * 60000, &msecs)
+            ? (bias < 0 ? Bound::min() + 1 : Bound::max())
+            : (msecs == Bound::min() ? msecs + 1 : msecs);
+    }
     return QTimeZonePrivate::invalidMSecs();
 }