Windows: allow cancelling long mount operations

Add a root-driver abort IOCTL that bypasses the mount control mutex and sets cooperative KDF abort flags for the active mount.

Restrict abort requests to privileged callers or to the user that initiated the pending mount, and retry early wait-dialog cancel requests until the driver has registered the cancellable mount context.

Wire the wait dialog Cancel button to send the abort request through a fresh driver handle, and propagate ERR_USER_ABORT through header/cache processing.

Add a /cancelmount command-line switch that sends the same abort request without displaying UI, so users can cancel hidden-wait-dialog mount operations from another process.

src/Common/Dlgcode.c

@@ -8880,12 +8880,18 @@ BOOL GetPhysicalDriveStorageInformation(UINT nDriveNumber, STORAGE_ACCESS_ALIGNM
 // implementation of the generic wait dialog mechanism
 
 static UINT g_wmWaitDlg = ::RegisterWindowMessage(L"VeraCryptWaitDlgMessage");
+#define WAIT_DLG_CANCEL_RETRY_TIMER_ID 1
+#define WAIT_DLG_CANCEL_RETRY_INTERVAL 250
+
+typedef BOOL (CALLBACK* WaitCancelProc)(void* pArg, HWND hWaitDlg);
 
 typedef struct
 {
 	HWND hwnd;
 	void* pArg;
 	WaitThreadProc callback;
+	WaitCancelProc cancelCallback;
+	BOOL cancelRequested;
 } WaitThreadParam;
 
 static void _cdecl WaitThread (void* pParam)
@@ -8899,6 +8905,22 @@ static void _cdecl WaitThread (void* pParam)
 	PostMessage (pThreadParam->hwnd, g_wmWaitDlg, 0, 0);
 }
 
+static BOOL WaitDlgTryCancel (HWND hwndDlg, WaitThreadParam* thParam)
+{
+	if (thParam && thParam->cancelCallback)
+	{
+		if (thParam->cancelCallback (thParam->pArg, hwndDlg))
+		{
+			KillTimer (hwndDlg, WAIT_DLG_CANCEL_RETRY_TIMER_ID);
+			return TRUE;
+		}
+
+		SetTimer (hwndDlg, WAIT_DLG_CANCEL_RETRY_TIMER_ID, WAIT_DLG_CANCEL_RETRY_INTERVAL, NULL);
+	}
+
+	return FALSE;
+}
+
 BOOL CALLBACK WaitDlgProc (HWND hwndDlg, UINT msg, WPARAM wParam, LPARAM lParam)
 {
 	WORD lw = LOWORD (wParam);
@@ -8908,6 +8930,7 @@ BOOL CALLBACK WaitDlgProc (HWND hwndDlg, UINT msg, WPARAM wParam, LPARAM lParam)
 	case WM_INITDIALOG:
 		{
 			WaitThreadParam* thParam = (WaitThreadParam*) lParam;
+			SetWindowLongPtr (hwndDlg, DWLP_USER, (LONG_PTR) thParam);
 
 			// set the progress bar type to MARQUEE (indefinite progress)
 			HWND hProgress = GetDlgItem (hwndDlg, IDC_WAIT_PROGRESS_BAR);
@@ -8935,24 +8958,50 @@ BOOL CALLBACK WaitDlgProc (HWND hwndDlg, UINT msg, WPARAM wParam, LPARAM lParam)
 			} 
 
 			LocalizeDialog (hwndDlg, NULL);
+			if (!thParam->cancelCallback)
+				ShowWindow (GetDlgItem (hwndDlg, IDCANCEL), SW_HIDE);
 			_beginthread(WaitThread, 0, thParam);
 			return 0;
 		}
 
 	case WM_COMMAND:
 
-		if (lw == IDOK || lw == IDCANCEL)
+		if (lw == IDCANCEL)
+		{
+			WaitThreadParam* thParam = (WaitThreadParam*) GetWindowLongPtr (hwndDlg, DWLP_USER);
+			if (thParam && thParam->cancelCallback && !thParam->cancelRequested)
+			{
+				thParam->cancelRequested = TRUE;
+				EnableWindow (GetDlgItem (hwndDlg, IDCANCEL), FALSE);
+				WaitDlgTryCancel (hwndDlg, thParam);
+			}
+			return 1;
+		}
+
+		if (lw == IDOK)
 			return 1;
 		else
 			return 0;
 
+	case WM_TIMER:
+		if (wParam == WAIT_DLG_CANCEL_RETRY_TIMER_ID)
+		{
+			WaitThreadParam* thParam = (WaitThreadParam*) GetWindowLongPtr (hwndDlg, DWLP_USER);
+			if (thParam && thParam->cancelRequested)
+				WaitDlgTryCancel (hwndDlg, thParam);
+			return 1;
+		}
+		return 0;
+
 	case WM_DESTROY:
+		KillTimer (hwndDlg, WAIT_DLG_CANCEL_RETRY_TIMER_ID);
 		DetachProtectionFromCurrentThread();
 		return 0;
 
 	default:
 		if (msg == g_wmWaitDlg)
 		{
+			KillTimer (hwndDlg, WAIT_DLG_CANCEL_RETRY_TIMER_ID);
 			EndDialog (hwndDlg, IDOK);
 			return 1;
 		}
@@ -9015,11 +9064,13 @@ static LRESULT CALLBACK ShowWaitDialogParentWndProc (HWND hWnd, UINT message, WP
 }
 
 
-void ShowWaitDialog(HWND hwnd, BOOL bUseHwndAsParent, WaitThreadProc callback, void* pArg)
+static void ShowWaitDialogEx(HWND hwnd, BOOL bUseHwndAsParent, WaitThreadProc callback, WaitCancelProc cancelCallback, void* pArg)
 {
 	BOOL bEffectiveHideWaitingDialog = bCmdHideWaitingDialogValid? bCmdHideWaitingDialog : bHideWaitingDialog;
 	WaitThreadParam threadParam;
 	threadParam.callback = callback;
+	threadParam.cancelCallback = cancelCallback;
+	threadParam.cancelRequested = FALSE;
 	threadParam.pArg = pArg;
 
 	if (WaitDialogDisplaying || bEffectiveHideWaitingDialog)
@@ -9082,6 +9133,11 @@ void ShowWaitDialog(HWND hwnd, BOOL bUseHwndAsParent, WaitThreadProc callback, v
 	}
 }
 
+void ShowWaitDialog(HWND hwnd, BOOL bUseHwndAsParent, WaitThreadProc callback, void* pArg)
+{
+	ShowWaitDialogEx (hwnd, bUseHwndAsParent, callback, NULL, pArg);
+}
+
 #ifndef SETUP
 /************************************************************************/
 
@@ -9108,6 +9164,26 @@ static BOOL PerformMountIoctl (MOUNT_STRUCT* pmount, LPDWORD pdwResult, BOOL use
 			sizeof (MOUNT_STRUCT), pmount, sizeof (MOUNT_STRUCT), pdwResult, NULL);
 }
 
+BOOL AbortMountOperation (int nDosDriveNo)
+{
+	BOOL bResult;
+	DWORD dwResult;
+	HANDLE hAbortDriver = CreateFile (WIN32_ROOT_PREFIX, 0, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, 0, NULL);
+	MOUNT_ABORT_STRUCT abortMount;
+
+	if (hAbortDriver == INVALID_HANDLE_VALUE)
+		return FALSE;
+
+	memset (&abortMount, 0, sizeof (abortMount));
+	abortMount.nDosDriveNo = nDosDriveNo;
+
+	bResult = DeviceIoControl (hAbortDriver, TC_IOCTL_ABORT_MOUNT_VOLUME, &abortMount,
+		sizeof (abortMount), &abortMount, sizeof (abortMount), &dwResult, NULL);
+
+	CloseHandle (hAbortDriver);
+	return bResult && abortMount.nReturnCode == ERR_USER_ABORT;
+}
+
 // specific definitions and implementation for support of mount operation 
 // in wait dialog mechanism
 
@@ -9130,6 +9206,13 @@ void CALLBACK MountWaitThreadProc(void* pArg, HWND )
 	pThreadParam->dwLastError = GetLastError ();
 }
 
+BOOL CALLBACK MountWaitCancelProc(void* pArg, HWND )
+{
+	MountThreadParam* pThreadParam = (MountThreadParam*) pArg;
+
+	return AbortMountOperation (pThreadParam->pmount->nDosDriveNo);
+}
+
 /************************************************************************/
 
 // Use only cached passwords if password = NULL
@@ -9366,7 +9449,7 @@ retry:
 		mountThreadParam.pdwResult = &dwResult;
 		mountThreadParam.dwLastError = ERROR_SUCCESS;
 
-		ShowWaitDialog (hwndDlg, FALSE, MountWaitThreadProc, &mountThreadParam);
+		ShowWaitDialogEx (hwndDlg, FALSE, MountWaitThreadProc, MountWaitCancelProc, &mountThreadParam);
 
 		dwLastError  = mountThreadParam.dwLastError;
 	}
@@ -9428,6 +9511,9 @@ retry:
 
 	if (mount.nReturnCode != 0)
 	{
+		if (mount.nReturnCode == ERR_USER_ABORT)
+			return -1;
+
 		if (mount.nReturnCode == ERR_PASSWORD_WRONG)
 		{
 			// Do not report wrong password, if not instructed to