Fix crash caused by objects self-destructions during displacement animations

The root cause was that the QAbstractAnimationJob::finished() might delegate its
destruction to change.listener->animationFinished(this), and the original author
was aware of that and provided a RETURN_IF_DELETE macro to return early if itself
got deleted. In the bug's case, change.listener->animationFinished(this)
dispatched to QQuickItemViewPrivate::animationFinished() which called
QQuickItemViewPrivate::release() and deleted the QAbstractAnimationJob object
itself in the end.

However, any objects derived from QAbstractAnimationJob, or holding a pointer
to a QAbstractAnimationJob, may potentially fall into the code path calling
QAbstractAnimationJob::finished(). Any QAnimationJobChangeListener that directly
or indirectly deletes QAbstractAnimationJob should be very suspicious to this
kind of "heap-use-after-free" bug. Should ensure that the QAbstractAnimationJob
won't be referenced after deletion.

In the bug's case, within the code path triggered by ListView displacement
animation, the other affected classes by QAbstractAnimationJob are:
QQuickItemViewFxItem, QQuickItemViewTransitionableItem, QQuickTransitionManager.

To fix this, a new SelfDeletable class is factored out to simplify the self-deletion
test logic. Any affected classes are made to have a public member m_selfDeletable.
Any code paths that finally reach QAbstractAnimationJob::finished() are
wrapped with related util macro.

Change-Id: Idd33fc3f2d529fd7d8bb088c329101b1e70dd6c0
Task-number: QTBUG-44308
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
 

1 files changed, 2 insertions, 0 deletions

diff --git a/src/quick/items/qquickitemviewfxitem.cpp b/src/quick/items/qquickitemviewfxitem.cpp
index f9c65967ea..16c2182962 100644
--- a/src/quick/items/qquickitemviewfxitem.cpp
+++ b/src/quick/items/qquickitemviewfxitem.cpp
@@ -56,6 +56,8 @@ QQuickItemViewFxItem::QQuickItemViewFxItem(QQuickItem *item, bool ownItem, QQuic
 QQuickItemViewFxItem::~QQuickItemViewFxItem()
 {
     delete transitionableItem;
+    transitionableItem = nullptr;
+
     if (ownItem && item) {
         trackGeometry(false);
         item->setParentItem(0);