Windows: mention 'Controlled Folder Access' on ERROR_ACCESS_DENIED

If WriteFile() returns ERROR_ACCESS_DENIED and registry indicates
CFA is on, tell user rpi-imager (and fat32format) should be added
to the "allowed apps" in the CFA settings.

downloadthread.cpp

@@ -18,6 +18,7 @@
 #include <regex>
 #include <QDebug>
 #include <QProcess>
+#include <QSettings>
 #include <QtConcurrent/QtConcurrent>
 
 #ifdef Q_OS_LINUX
@@ -34,7 +35,7 @@ int DownloadThread::_curlCount = 0;
 DownloadThread::DownloadThread(const QByteArray &url, const QByteArray &localfilename, const QByteArray &expectedHash, QObject *parent) :
     QThread(parent), _startOffset(0), _lastDlTotal(0), _lastDlNow(0), _verifyTotal(0), _lastVerifyNow(0), _bytesWritten(0), _sectorsStart(-1), _url(url), _filename(localfilename), _expectedHash(expectedHash),
     _firstBlock(nullptr), _cancelled(false), _successful(false), _verifyEnabled(false), _cacheEnabled(false), _lastModified(0), _serverTime(0),  _lastFailureTime(0),
-    _file(NULL), _writehash(OSLIST_HASH_ALGORITHM), _verifyhash(OSLIST_HASH_ALGORITHM), _inputBufferSize(0)
+    _inputBufferSize(0), _file(NULL), _writehash(OSLIST_HASH_ALGORITHM), _verifyhash(OSLIST_HASH_ALGORITHM)
 {
     if (!_curlCount)
         curl_global_init(CURL_GLOBAL_DEFAULT);
@@ -333,7 +334,22 @@ void DownloadThread::run()
             break;
         case CURLE_WRITE_ERROR:
             deleteDownloadedFile();
-            _onDownloadError("Error writing file to disk");
+
+#ifdef Q_OS_WIN
+            if (_file.errorCode() == ERROR_ACCESS_DENIED)
+            {
+                QString msg = tr("Access denied error while writing file to disk.");
+                QSettings registry("HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Windows Defender\\Windows Defender Exploit Guard\\Controlled Folder Access",
+                                   QSettings::Registry64Format);
+                if (registry.value("EnableControlledFolderAccess").toInt() == 1)
+                {
+                    msg += "<br>"+tr("Controlled Folder Access seems to be enabled. Please add both rpi-imager.exe and fat32format.exe to the list of allowed apps and try again.");
+                }
+                _onDownloadError(msg);
+            }
+            else
+#endif
+                _onDownloadError(tr("Error writing file to disk"));
             break;
         case CURLE_ABORTED_BY_CALLBACK:
             deleteDownloadedFile();
@@ -619,10 +635,10 @@ void DownloadThread::_writeComplete()
     eject_disk(_filename.constData());
 
 #ifdef Q_OS_WIN
-    QStringList args = {"start", "StorSvc"};
+    QStringList args2 = {"start", "StorSvc"};
     QProcess *p2 = new QProcess(this);
     qDebug() << "Restarting storage services";
-    p2->startDetached("net", args);
+    p2->startDetached("net", args2);
 #endif
 
     emit success();

windows/winfile.cpp

@@ -8,7 +8,7 @@
 #include <QThread>
 
 WinFile::WinFile(QObject *parent)
-    : QObject(parent), _locked(false), _h(INVALID_HANDLE_VALUE)
+    : QObject(parent), _locked(false), _h(INVALID_HANDLE_VALUE), _lasterrorcode(0)
 {
 
 }
@@ -44,6 +44,7 @@ bool WinFile::open(QIODevice::OpenMode)
 
     if (_h == INVALID_HANDLE_VALUE)
     {
+        _lasterrorcode = GetLastError();
         _lasterror = qt_error_string();
         qDebug() << "Error opening:" << _lasterror;
         return false;
@@ -80,6 +81,7 @@ qint64 WinFile::write(const char *data, qint64 maxSize)
 
     if (!WriteFile(_h, data, maxSize, &bytesWritten, NULL))
     {
+        _lasterrorcode = GetLastError();
         _lasterror = qt_error_string();
         return -1;
     }
@@ -93,6 +95,7 @@ qint64 WinFile::read(char *data, qint64 maxSize)
 
     if (!ReadFile(_h, data, maxSize, &bytesRead, NULL))
     {
+        _lasterrorcode = GetLastError();
         _lasterror = qt_error_string();
         return -1;
     }
@@ -107,6 +110,7 @@ bool WinFile::seek(qint64 pos)
     offset.QuadPart = pos;
     if (!SetFilePointerEx(_h, offset, &current, FILE_BEGIN))
     {
+        _lasterrorcode = GetLastError();
         _lasterror = qt_error_string();
         qDebug() << "Error seeking:" << _lasterror;
         return false;
@@ -122,6 +126,7 @@ qint64 WinFile::pos()
     offset.QuadPart = 0;
     if (!SetFilePointerEx(_h, offset, &current, FILE_CURRENT))
     {
+        _lasterrorcode = GetLastError();
         _lasterror = qt_error_string();
         return 0;
     }
@@ -139,6 +144,11 @@ QString WinFile::errorString() const
     return _lasterror;
 }
 
+int WinFile::errorCode() const
+{
+    return _lasterrorcode;
+}
+
 bool WinFile::flush()
 {
     if (!FlushFileBuffers(_h))

windows/winfile.h

@@ -24,6 +24,7 @@ public:
     qint64 read(char *data, qint64 maxSize);
     HANDLE handle();
     QString errorString() const;
+    int errorCode() const;
     bool flush();
     bool seek(qint64 pos);
     qint64 pos();
@@ -34,6 +35,7 @@ protected:
     bool _locked;
     QString _name, _lasterror;
     HANDLE _h;
+    int _lasterrorcode;
 };
 
 #endif // WINFILE_H