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a11y: Do not refer to destructed QObject in Windows bridge

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The crash could happen if a QWidget in the UI got deleted, and
the AT client later tried to access the widget through the cache
(qAccessibleRecentSentEvents()).

Solution: Use a QPointer as a guard.

Task-number: QTBUG-26187

Change-Id: I1aa716766626cf171757e76ba255a6d5ae4fd854
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
This commit is contained in:
Jan Arve Saether 2012-12-07 15:29:06 +01:00 committed by The Qt Project
parent 03e1e4138c
commit ced154500d
2 changed files with 22 additions and 10 deletions
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28
src/plugins/platforms/windows/accessible/qwindowsaccessibility.cpp
View File

@ -48,6 +48,7 @@
#include <QtCore/qlocale.h>
#include <QtCore/qmap.h>
#include <QtCore/qpair.h>
#include <QtCore/qpointer.h>
#include <QtCore/qsettings.h>
#include <QtGui/qaccessible.h>
#include <QtGui/qaccessible2.h>
@ -87,10 +88,9 @@
// This stuff is used for widgets/items with no window handle:
typedef QMap<int, QPair<QObject*,int> > NotifyMap;
typedef QMap<int, QPair<QPointer<QObject>,int> > NotifyMap;
Q_GLOBAL_STATIC(NotifyMap, qAccessibleRecentSentEvents)
QT_BEGIN_NAMESPACE
@ -193,14 +193,25 @@ void QWindowsAccessibility::notifyAccessibilityUpdate(QAccessibleEvent *event)
HWND hWnd = (HWND)platform->nativeResourceForWindow("handle", window);
static int eventNum = 0;
if (event->type() != QAccessible::MenuCommand) { // MenuCommand is faked
// See comment "SENDING EVENTS TO OBJECTS WITH NO WINDOW HANDLE"
if (event->type() != QAccessible::MenuCommand && // MenuCommand is faked
event->type() != QAccessible::ObjectDestroyed) {
/* In some rare occasions, the server (Qt) might get a ::get_accChild call with a
childId that references an entry in the cache where there was a dangling
QObject-pointer. Previously we crashed on this.
There is no point in actually notifying the AT client that the object got destroyed,
because the AT client won't query for get_accChild if the event is ObjectDestroyed
anyway, and we have no other way of mapping the eventId argument to the actual
child/descendant object. (Firefox seems to simply completely ignore
EVENT_OBJECT_DESTROY).
We therefore guard each QObject in the cache with a QPointer, and only notify the AT
client if the type is not ObjectDestroyed.
*/
eventNum %= 50; //[0..49]
int eventId = - (eventNum - 1);
qAccessibleRecentSentEvents()->insert(eventId, qMakePair(event->object(), event->child()));
qAccessibleRecentSentEvents()->insert(eventId, qMakePair(QPointer<QObject>(event->object()), event->child()));
ptrNotifyWinEvent(event->type(), hWnd, OBJID_CLIENT, eventId);
++eventNum;
}
#endif // Q_OS_WINCE
@ -244,7 +255,8 @@ IAccessible *QWindowsAccessibility::wrap(QAccessibleInterface *acc)
*/
QPair<QObject*, int> QWindowsAccessibility::getCachedObject(int entryId)
{
return qAccessibleRecentSentEvents()->value(entryId);
QPair<QPointer<QObject>, int> pair = qAccessibleRecentSentEvents()->value(entryId);
return qMakePair(pair.first.data(), pair.second);
}
/*

2
src/plugins/platforms/windows/accessible/qwindowsmsaaaccessible.cpp
View File

@ -757,7 +757,7 @@ HRESULT STDMETHODCALLTYPE QWindowsMsaaAccessible::get_accChild(VARIANT varChildI
acc = res;
}
} else {
qWarning("get_accChild got a negative varChildID, but did not find it in cache");
qWarning("get_accChild got a negative varChildID (%d), but did not find it in cache", childIndex);
}
} else {
if (childIndex) {