tdf#132940 Crash in mergedlo!vcl::Region::operator=

We had a SdrPageWindow accessing a SdPaintWindow that had already been
freed.
Turns that SdrPageWindow can be "patched" more than once given enough
stuff going on in writer, so make the call sites restore the previous
state as the stack unwinds.

Change-Id: Ia1ef5c9b2f818b7873e8e739c9cdf257554e403a
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/101044
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
(cherry picked from commit 445cf499666f21c2d480ce1df9ce6004b9450b64)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/101450

2 files changed, 32 insertions, 12 deletions

diff --git a/svx/source/svdraw/sdrpagewindow.cxx b/svx/source/svdraw/sdrpagewindow.cxx
index fb3155c0eb14..6d197dab5282 100644
--- a/svx/source/svdraw/sdrpagewindow.cxx
+++ b/svx/source/svdraw/sdrpagewindow.cxx
@@ -163,22 +163,41 @@ rtl::Reference< sdr::overlay::OverlayManager > const & SdrPageWindow::GetOverlay
     return GetPaintWindow().GetOverlayManager();
 }
 
-void SdrPageWindow::patchPaintWindow(SdrPaintWindow& rPaintWindow)
+SdrPaintWindow* SdrPageWindow::patchPaintWindow(SdrPaintWindow& rPaintWindow)
 {
-    mpImpl->mpOriginalPaintWindow = mpImpl->mpPaintWindow;
-    mpImpl->mpPaintWindow = &rPaintWindow;
-    mpImpl->mpOriginalPaintWindow->setPatched(&rPaintWindow);
+    if (!mpImpl->mpOriginalPaintWindow)
+    {
+        // first patch
+        mpImpl->mpOriginalPaintWindow = mpImpl->mpPaintWindow;
+        mpImpl->mpPaintWindow = &rPaintWindow;
+        mpImpl->mpOriginalPaintWindow->setPatched(&rPaintWindow);
+        return mpImpl->mpOriginalPaintWindow;
+    }
+    else
+    {
+        // second or more patch
+        auto pPreviousPaintWindow = mpImpl->mpPaintWindow;
+        mpImpl->mpPaintWindow = &rPaintWindow;
+        mpImpl->mpOriginalPaintWindow->setPatched(&rPaintWindow);
+        return pPreviousPaintWindow;
+    }
 }
 
-void SdrPageWindow::unpatchPaintWindow()
+void SdrPageWindow::unpatchPaintWindow(SdrPaintWindow* pPreviousPaintWindow)
 {
-    DBG_ASSERT(mpImpl->mpOriginalPaintWindow, "SdrPageWindow::unpatchPaintWindow: paint window not patched!" );
-    if (mpImpl->mpOriginalPaintWindow)
+    if (pPreviousPaintWindow == mpImpl->mpOriginalPaintWindow)
     {
+        // first patch
         mpImpl->mpPaintWindow = mpImpl->mpOriginalPaintWindow;
         mpImpl->mpOriginalPaintWindow->setPatched(nullptr);
         mpImpl->mpOriginalPaintWindow = nullptr;
     }
+    else
+    {
+        // second or more patch
+        mpImpl->mpPaintWindow = pPreviousPaintWindow;
+        mpImpl->mpOriginalPaintWindow->setPatched(pPreviousPaintWindow);
+    }
 }
 
 void SdrPageWindow::PrePaint()
diff --git a/svx/source/svdraw/svdpagv.cxx b/svx/source/svdraw/svdpagv.cxx
index 215e37bc7c94..480182782984 100644
--- a/svx/source/svdraw/svdpagv.cxx
+++ b/svx/source/svdraw/svdpagv.cxx
@@ -32,6 +32,7 @@
 #include <svx/sdrpagewindow.hxx>
 #include <svx/sdrpaintwindow.hxx>
 #include <comphelper/lok.hxx>
+#include <comphelper/scopeguard.hxx>
 #include <basegfx/range/b2irectangle.hxx>
 
 using namespace ::com::sun::star;
@@ -290,13 +291,13 @@ void SdrPageView::DrawLayer(SdrLayerID nID, OutputDevice* pGivenTarget,
                     else
                         aTemporaryPaintWindow.SetRedrawRegion(vcl::Region(rRect));
                     // patch the ExistingPageWindow
-                    pPreparedTarget->patchPaintWindow(aTemporaryPaintWindow);
-
+                    auto pPreviousWindow = pPreparedTarget->patchPaintWindow(aTemporaryPaintWindow);
+                    // unpatch window when leaving the scope
+                    const ::comphelper::ScopeGuard aGuard(
+                        [&pPreviousWindow, &pPreparedTarget]() { pPreparedTarget->unpatchPaintWindow(pPreviousWindow); } );
+                    
                     // redraw the layer
                     pPreparedTarget->RedrawLayer(&nID, pRedirector, pPageFrame);
-
-                    // restore the ExistingPageWindow
-                    pPreparedTarget->unpatchPaintWindow();
                 }
                 else
                 {