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QTzTimeZonePrivate: fix UB (data race on m_icu)

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The fallback m_icu QIcuTimeZonePrivate is lazily constructed, which
means that two threads each with their own copy of a QTimeZone with a
shared QTzTimeZonePrivate will race over who gets to set m_icu,
e.g. when concurrently calling QTimeZone::displayName().

Fix by protecting m_icu with a mutex. For simplicity, use a static
mutex, not a per-instance one (which would delete the
QTzTimeZonePrivate copy constructor, which clone() relies on). This is
sufficient for 5.15. For Qt 6, going forward, we could make this
lock-less, too.

[ChangeLog][QtCore][QTimeZone] Fixed a data race on Unix platforms when
implicitly-shared copies of QTimeZone objects were used in certain ways
(e.g. calling displayName()) from different threads and Qt was
configured with ICU support.

Pick-to: 6.3 6.2 5.15
Change-Id: I7e57aef3dd44a90289ad86d0578ece1e54920730
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
This commit is contained in:
Marc Mutz 2022-01-04 18:03:22 +01:00
parent bfc713530a
commit 11becbe910
1 changed files with 12 additions and 0 deletions
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12
src/corelib/time/qtimezoneprivate_tz.cpp
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@ -42,6 +42,7 @@
#include "qtimezone.h"
#include "qtimezoneprivate_p.h"
#include "private/qlocale_tools_p.h"
#include "private/qlocking_p.h"
#include <QtCore/QDataStream>
#include <QtCore/QDateTime>
@ -62,6 +63,10 @@
QT_BEGIN_NAMESPACE
#if QT_CONFIG(icu)
static QBasicMutex s_icu_mutex;
#endif
/*
Private
@ -729,6 +734,9 @@ QTzTimeZonePrivate::~QTzTimeZonePrivate()
QTzTimeZonePrivate *QTzTimeZonePrivate::clone() const
{
#if QT_CONFIG(icu)
const auto lock = qt_scoped_lock(s_icu_mutex);
#endif
return new QTzTimeZonePrivate(*this);
}
@ -989,12 +997,14 @@ QString QTzTimeZonePrivate::displayName(qint64 atMSecsSinceEpoch,
const QLocale &locale) const
{
#if QT_CONFIG(icu)
auto lock = qt_unique_lock(s_icu_mutex);
if (!m_icu)
m_icu = new QIcuTimeZonePrivate(m_id);
// TODO small risk may not match if tran times differ due to outdated files
// TODO Some valid TZ names are not valid ICU names, use translation table?
if (m_icu->isValid())
return m_icu->displayName(atMSecsSinceEpoch, nameType, locale);
lock.unlock();
#else
Q_UNUSED(nameType);
Q_UNUSED(locale);
@ -1008,12 +1018,14 @@ QString QTzTimeZonePrivate::displayName(QTimeZone::TimeType timeType,
const QLocale &locale) const
{
#if QT_CONFIG(icu)
auto lock = qt_unique_lock(s_icu_mutex);
if (!m_icu)
m_icu = new QIcuTimeZonePrivate(m_id);
// TODO small risk may not match if tran times differ due to outdated files
// TODO Some valid TZ names are not valid ICU names, use translation table?
if (m_icu->isValid())
return m_icu->displayName(timeType, nameType, locale);
lock.unlock();
#else
Q_UNUSED(timeType);
Q_UNUSED(nameType);