Windows/QProcess::startDetached(): Fall back to ShellExecuteEx() for UAC prompt.

When running a process that requires elevated privileges (such as
regedt32 or an installer), the Win32 API CreateProcess fails
with error ERROR_ELEVATION_REQUIRED.
Fall back to ShellExecuteEx() using the verb "runas" in that case,
bringing up the UAC prompt.

Task-number: QTBUG-7645
Change-Id: Iee82a86a30f78c5a49246d2c0d4566306f3afc71
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>

1 files changed, 40 insertions, 0 deletions

diff --git a/src/corelib/io/qprocess_win.cpp b/src/corelib/io/qprocess_win.cpp
index e7cd9d9a17..7e9cffe129 100644
--- a/src/corelib/io/qprocess_win.cpp
+++ b/src/corelib/io/qprocess_win.cpp
@@ -42,6 +42,7 @@
 #include <qfileinfo.h>
 #include <qregexp.h>
 #include <qwineventnotifier.h>
+#include <private/qsystemlibrary_p.h>
 #include <private/qthread_p.h>
 #include <qdebug.h>
 
@@ -808,8 +809,45 @@ bool QProcessPrivate::waitForWrite(int msecs)
     return false;
 }
 
+// Use ShellExecuteEx() to trigger an UAC prompt when CreateProcess()fails
+// with ERROR_ELEVATION_REQUIRED.
+static bool startDetachedUacPrompt(const QString &programIn, const QStringList &arguments,
+                                   const QString &workingDir, qint64 *pid)
+{
+    typedef BOOL (WINAPI *ShellExecuteExType)(SHELLEXECUTEINFOW *);
+
+    static const ShellExecuteExType shellExecuteEx = // XP ServicePack 1 onwards.
+        reinterpret_cast<ShellExecuteExType>(QSystemLibrary::resolve(QLatin1String("shell32"),
+                                                                     "ShellExecuteExW"));
+    if (!shellExecuteEx)
+        return false;
+
+    const QString args = qt_create_commandline(QString(), arguments); // needs arguments only
+    SHELLEXECUTEINFOW shellExecuteExInfo;
+    memset(&shellExecuteExInfo, 0, sizeof(SHELLEXECUTEINFOW));
+    shellExecuteExInfo.cbSize = sizeof(SHELLEXECUTEINFOW);
+    shellExecuteExInfo.fMask = SEE_MASK_NOCLOSEPROCESS | SEE_MASK_UNICODE | SEE_MASK_FLAG_NO_UI;
+    shellExecuteExInfo.lpVerb = L"runas";
+    const QString program = QDir::toNativeSeparators(programIn);
+    shellExecuteExInfo.lpFile = reinterpret_cast<LPCWSTR>(program.utf16());
+    if (!args.isEmpty())
+        shellExecuteExInfo.lpParameters = reinterpret_cast<LPCWSTR>(args.utf16());
+    if (!workingDir.isEmpty())
+        shellExecuteExInfo.lpDirectory = reinterpret_cast<LPCWSTR>(workingDir.utf16());
+    shellExecuteExInfo.nShow = SW_SHOWNORMAL;
+
+    if (!shellExecuteEx(&shellExecuteExInfo))
+        return false;
+    if (pid)
+        *pid = qint64(GetProcessId(shellExecuteExInfo.hProcess));
+    CloseHandle(shellExecuteExInfo.hProcess);
+    return true;
+}
+
 bool QProcessPrivate::startDetached(const QString &program, const QStringList &arguments, const QString &workingDir, qint64 *pid)
 {
+    static const DWORD errorElevationRequired = 740;
+
     QString args = qt_create_commandline(program, arguments);
     bool success = false;
     PROCESS_INFORMATION pinfo;
@@ -829,6 +867,8 @@ bool QProcessPrivate::startDetached(const QString &program, const QStringList &a
         CloseHandle(pinfo.hProcess);
         if (pid)
             *pid = pinfo.dwProcessId;
+    } else if (GetLastError() == errorElevationRequired) {
+        success = startDetachedUacPrompt(program, arguments, workingDir, pid);
     }
 
     return success;