QCborValue: avoid signed integer oveflows when decoding time_t

QDateTime::fromSecsSinceEpoch() multiplies by 1000 but does not check
for overflow. That means we must do so in QCborValue validation. We
can't use mul_overflow<qint64> on 32-bit platforms, so we do a compare-
and-branch there. For 64-bit platforms, we prefer to do the
multiplication with checked overflow, as the common case is that it will
not overflow and we'll need the multiplication anyway.

Change-Id: Ibdc95e9af7bd456a94ecfffd16060cba6f1c86b8
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/corelib/serialization/qcborvalue.cpp

@@ -788,10 +788,25 @@ static QCborValue::Type convertToExtendedType(QCborContainerPrivate *d)
             // The data is supposed to be US-ASCII. If it isn't (contains UTF-8),
             // QDateTime::fromString will fail anyway.
             dt = QDateTime::fromString(b->asLatin1(), Qt::ISODateWithMs);
-        } else if (tag == qint64(QCborKnownTags::UnixTime_t) && e.type == QCborValue::Integer) {
-            dt = QDateTime::fromSecsSinceEpoch(e.value, Qt::UTC);
-        } else if (tag == qint64(QCborKnownTags::UnixTime_t) && e.type == QCborValue::Double) {
-            dt = QDateTime::fromMSecsSinceEpoch(qint64(e.fpvalue() * 1000), Qt::UTC);
+        } else if (tag == qint64(QCborKnownTags::UnixTime_t)) {
+            qint64 msecs;
+            bool ok = false;
+            if (e.type == QCborValue::Integer) {
+#if QT_POINTER_SIZE == 8
+                // we don't have a fast 64-bit mul_overflow implementation on
+                // 32-bit architectures.
+                ok = !mul_overflow(e.value, qint64(1000), &msecs);
+#else
+                static const qint64 Limit = std::numeric_limits<qint64>::max() / 1000;
+                ok = (e.value > -Limit && e.value < Limit);
+                if (ok)
+                    msecs = e.value * 1000;
+#endif
+            } else if (e.type == QCborValue::Double) {
+                ok = convertDoubleTo(round(e.fpvalue() * 1000), &msecs);
+            }
+            if (ok)
+                dt = QDateTime::fromMSecsSinceEpoch(msecs, Qt::UTC);
         }
         if (dt.isValid()) {
             QByteArray text = dt.toString(Qt::ISODateWithMs).toLatin1();

tests/auto/corelib/serialization/qcborvalue/tst_qcborvalue.cpp

@@ -106,6 +106,8 @@ private slots:
     void fromCborStreamReaderIODevice();
     void validation_data();
     void validation();
+    void extendedTypeValidation_data();
+    void extendedTypeValidation();
     void hugeDeviceValidation_data();
     void hugeDeviceValidation();
     void recursionLimit_data();
@@ -118,6 +120,68 @@ private slots:
     void streamVariantSerialization();
 };
 
+namespace SimpleEncodeToCbor {
+inline size_t lengthOf(int)
+{
+    return 1;       // encode as byte
+}
+
+template <typename T> inline size_t lengthOf(T)
+{
+    return sizeof(T);
+}
+
+static void encodeOneAt(char *ptr, int v)
+{
+    // encode as byte
+    *ptr = char(v);
+}
+
+template <typename T>
+static typename std::enable_if<std::is_unsigned<T>::value>::type
+encodeOneAt(char *ptr, T v)
+{
+    qToBigEndian(v, ptr);
+}
+
+template <typename T>
+static typename std::enable_if<std::is_floating_point<T>::value ||
+                               std::is_same<T, qfloat16>::value>::type
+encodeOneAt(char *ptr, T v)
+{
+    typename QIntegerForSizeof<T>::Unsigned u;
+    memcpy(&u, &v, sizeof(u));
+    qToBigEndian(u, ptr);
+}
+
+static char *encodeAt(char *ptr)
+{
+    return ptr;
+}
+
+template <typename Arg0, typename... Args>
+static char *encodeAt(char *ptr, Arg0 a0, Args... a)
+{
+    encodeOneAt(ptr, a0);
+    return encodeAt(ptr + lengthOf(a0), a...);
+}
+
+} // namespace SimpleEncodetoCbor
+
+template <typename... Args>
+static QByteArray encode(Args... a)
+{
+    // this would be much easier with C++17 fold expressions...
+    using namespace SimpleEncodeToCbor;
+    using namespace std;
+    size_t lengths[] = { lengthOf(a)... };
+    size_t total = accumulate(begin(lengths), end(lengths), size_t(0), plus<size_t>{});
+    QByteArray result(QByteArray::size_type(total), Qt::Uninitialized);
+    char *ptr = result.data();
+    encodeAt(ptr, a...);
+    return result;
+}
+
 // Get the validation data from TinyCBOR (see src/3rdparty/tinycbor/tests/parser/data.cpp)
 #include "data.cpp"
 
@@ -1882,6 +1946,51 @@ void tst_QCborValue::validation()
     }
 }
 
+void tst_QCborValue::extendedTypeValidation_data()
+{
+    QTest::addColumn<QByteArray>("data");
+    QTest::addColumn<QCborValue>("expected");
+
+    // QDateTime currently stores time in milliseconds, so make sure
+    // we don't overflow
+    {
+        quint64 limit = std::numeric_limits<quint64>::max() / 1000;
+        QTest::newRow("UnixTime_t:integer-overflow-positive")
+                << encode(0xc1, 0x1b, limit + 1)
+                << QCborValue(QCborKnownTags::UnixTime_t, qint64(limit) + 1);
+        QTest::newRow("UnixTime_t:integer-overflow-negative")
+                << encode(0xc1, 0x3b, limit)
+                << QCborValue(QCborKnownTags::UnixTime_t, -qint64(limit) - 1);
+
+        double fplimit = std::numeric_limits<qint64>::min() / (-1000.); // 2^63 ms
+        QTest::newRow("UnixTime_t:fp-overflow-positive")
+                << encode(0xc1, 0xfb, fplimit)
+                << QCborValue(QCborKnownTags::UnixTime_t, fplimit);
+        QTest::newRow("UnixTime_t:fp-overflow-negative")
+                << encode(0xc1, 0xfb, -fplimit)
+                << QCborValue(QCborKnownTags::UnixTime_t, -fplimit);
+    }
+}
+
+void tst_QCborValue::extendedTypeValidation()
+{
+    QFETCH(QByteArray, data);
+    QFETCH(QCborValue, expected);
+
+    QCborParserError error;
+    QCborValue decoded = QCborValue::fromCbor(data, &error);
+    QVERIFY2(error.error == QCborError(), qPrintable(error.errorString()));
+    QCOMPARE(error.offset, data.size());
+    QCOMPARE(decoded, expected);
+
+    QByteArray encoded = decoded.toCbor();
+#if QT_VERSION < QT_VERSION_CHECK(6,0,0)
+    // behavior change, see qdatetime.cpp:fromIsoTimeString
+    QEXPECT_FAIL("DateTime:Null-at-19", "QDateTime parsing fixed, but only in 6.0", Abort);
+#endif
+    QCOMPARE(encoded, data);
+}
+
 void tst_QCborValue::hugeDeviceValidation_data()
 {
     addValidationHugeDevice(MaxByteArraySize + 1, MaxStringSize + 1);