qputenv: defend against non-NUL-terminated QByteArray values

The old code assumed that a QByteArray's data() is always
NUL-terminated. Due to the conflation of owners and non-owners in
QByteArray (but also in case we ever get efficient substringing), this
is not always the case, e.g. QByteArray::fromRawData() does not ensure
NUL-termination.

From QString::utf16(), we learn that the condition to check for is
QArrayData::isMutable(). After working around the fact that
QByteArray::data_ptr() doesn't exist for const QBAs and that empty
QBAs always refer to QByteArray::empty_, which is !isMutable(), we can
detect this situation and re-allocate without introducing new API.

This is the fix for Qt ≤ 6.4. For Qt 6.5, we'll port the function to
QByteArrayView.

Pick-to: 6.4 6.3 6.2 5.15
Fixes: QTBUG-105302
Change-Id: I3416535ab09d601e0e87b2767f2c024ba1217e64
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/global/qenvironmentvariables.cpp

@@ -262,6 +262,14 @@ bool qEnvironmentVariableIsSet(const char *varName) noexcept
 */
 bool qputenv(const char *varName, const QByteArray &value)
 {
+    // protect against non-NUL-terminated QByteArrays:
+    if (!const_cast<QByteArray&>(value).data_ptr()->isMutable()) {
+        QByteArray copy(value);
+        copy.reserve(copy.size() + 1); // ensures NUL termination (and isMutable() even for size==0
+                                       // (unlike detach()) to avoid infinite recursion)
+        return qputenv(varName, copy);
+    }
+
 #if defined(Q_CC_MSVC)
     const auto locker = qt_scoped_lock(environmentMutex);
     return _putenv_s(varName, value.constData()) == 0;

tests/auto/corelib/global/qgetputenv/tst_qgetputenv.cpp

@@ -60,7 +60,11 @@ void tst_QGetPutEnv::getSetCheck()
     QCOMPARE(sresult, QString());
 #endif
 
-    QVERIFY(qputenv(varName, QByteArray("supervalue")));
+    constexpr char varValueFullString[] = "supervalue123";
+    const auto varValueQBA = QByteArray::fromRawData(varValueFullString, sizeof varValueFullString - 4);
+    QCOMPARE_EQ(varValueQBA, "supervalue");
+
+    QVERIFY(qputenv(varName, varValueQBA));
 
     QVERIFY(qEnvironmentVariableIsSet(varName));
     QVERIFY(!qEnvironmentVariableIsEmpty(varName));