Windows: Fix QLockFile hanging when file cannot be created.

Return QLockFile::PermissionError when file does not exist, preventing
the stale file detection logic from triggering.

Add Windows-only autotest trying to create a lock file in
a system folder guarded with checks for elevated processes
and UAC virtualization.

Task-number: QTBUG-45631
Change-Id: I1790f8f925660f6bf1df94c2ced901e6ec57cbb0
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>
Reviewed-by: Oliver Wolff <oliver.wolff@theqtcompany.com>

src/corelib/io/qlockfile_win.cpp

@@ -48,6 +48,12 @@ static inline QByteArray localHostName()
     return qgetenv("COMPUTERNAME");
 }
 
+static inline bool fileExists(const wchar_t *fileName)
+{
+    WIN32_FILE_ATTRIBUTE_DATA  data;
+    return GetFileAttributesEx(fileName, GetFileExInfoStandard, &data);
+}
+
 QLockFile::LockError QLockFilePrivate::tryLock_sys()
 {
     const QFileSystemEntry fileEntry(fileName);
@@ -79,8 +85,13 @@ QLockFile::LockError QLockFilePrivate::tryLock_sys()
         case ERROR_SHARING_VIOLATION:
         case ERROR_ALREADY_EXISTS:
         case ERROR_FILE_EXISTS:
-        case ERROR_ACCESS_DENIED: // readonly file, or file still in use by another process. Assume the latter, since we don't create it readonly.
             return QLockFile::LockFailedError;
+        case ERROR_ACCESS_DENIED:
+            // readonly file, or file still in use by another process.
+            // Assume the latter if the file exists, since we don't create it readonly.
+            return fileExists((const wchar_t*)fileEntry.nativeFilePath().utf16())
+                ? QLockFile::LockFailedError
+                : QLockFile::PermissionError;
         default:
             qWarning() << "Got unexpected locking error" << lastError;
             return QLockFile::UnknownError;

tests/auto/corelib/io/qlockfile/tst_qlockfile.cpp

@@ -36,8 +36,11 @@
 #include <QtConcurrentRun>
 #include <qlockfile.h>
 #include <qtemporarydir.h>
+#include <qsysinfo.h>
 #if defined(Q_OS_UNIX) && !defined(Q_OS_VXWORKS)
 #include <unistd.h>
+#elif defined(Q_OS_WIN) && !defined(Q_OS_WINCE) && !defined(Q_OS_WINRT)
+#  include <qt_windows.h>
 #endif
 
 class tst_QLockFile : public QObject
@@ -58,6 +61,7 @@ private slots:
     void staleLongLockFromBusyProcess();
     void staleLockRace();
     void noPermissions();
+    void noPermissionsWindows();
 
 public:
     QString m_helperApp;
@@ -415,5 +419,66 @@ void tst_QLockFile::noPermissions()
     QCOMPARE(int(lockFile.error()), int(QLockFile::PermissionError));
 }
 
+enum ProcessProperty {
+    ElevatedProcess = 0x1,
+    VirtualStore = 0x2
+};
+
+Q_DECLARE_FLAGS(ProcessProperties, ProcessProperty)
+Q_DECLARE_OPERATORS_FOR_FLAGS(ProcessProperties)
+
+static inline ProcessProperties processProperties()
+{
+    ProcessProperties result;
+#if defined(Q_OS_WIN) && !defined(Q_OS_WINCE) && !defined(Q_OS_WINRT)
+    HANDLE processToken = NULL;
+    if (OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY, &processToken)) {
+        DWORD elevation; // struct containing a DWORD, not present in some MinGW headers.
+        DWORD cbSize = sizeof(elevation);
+        if (GetTokenInformation(processToken, TokenElevation, &elevation, cbSize, &cbSize)
+            && elevation) {
+            result |= ElevatedProcess;
+        }
+        // Check for UAC virtualization (compatibility mode for old software
+        // allowing it to write to system folders by mirroring them under
+        // "\Users\...\AppData\Local\VirtualStore\", which is typically the case
+        // for MinGW).
+        DWORD virtualStoreEnabled = 0;
+        cbSize = sizeof(virtualStoreEnabled);
+        if (GetTokenInformation(processToken, TokenVirtualizationEnabled, &virtualStoreEnabled, cbSize, &cbSize)
+            && virtualStoreEnabled) {
+            result |= VirtualStore;
+        }
+        CloseHandle(processToken);
+    }
+#endif
+    return result;
+}
+
+void tst_QLockFile::noPermissionsWindows()
+{
+    // Windows: Do the permissions test in a system directory in which
+    // files cannot be created.
+#if !defined(Q_OS_WIN) || defined(Q_OS_WINCE) || defined(Q_OS_WINRT)
+    QSKIP("This test is for desktop Windows only");
+#endif
+#ifdef Q_OS_WIN
+    if (QSysInfo::windowsVersion() < QSysInfo::WV_WINDOWS7)
+        QSKIP("This test requires at least Windows 7");
+#endif
+    if (const int p = processProperties()) {
+        const QByteArray message = "This test cannot be run (properties=0x"
+            + QByteArray::number(p, 16) + ')';
+        QSKIP(message.constData());
+    }
+
+    const QString fileName = QFile::decodeName(qgetenv("ProgramFiles"))
+        + QLatin1Char('/') + QCoreApplication::applicationName()
+        + QDateTime::currentDateTime().toString(QStringLiteral("yyMMddhhmm"));
+    QLockFile lockFile(fileName);
+    QVERIFY(!lockFile.lock());
+    QCOMPARE(int(lockFile.error()), int(QLockFile::PermissionError));
+}
+
 QTEST_MAIN(tst_QLockFile)
 #include "tst_qlockfile.moc"

tests/auto/corelib/io/qlockfile/tst_qlockfile.pro

@@ -4,3 +4,4 @@ TARGET = tst_qlockfile
 SOURCES += tst_qlockfile.cpp
 
 QT = core testlib concurrent
+win32:!wince:!winrt:LIBS += -ladvapi32