Fix heap use after free in CPDFSDK_Annot::GetPDFAnnot.

Use two seperate loops to kill current focus annot and to release annots
in current page. Loop to kill current focus annot is run first, so it
will not access deleted annots.

BUG=507316

R=tsepez@chromium.org

TEST=Reproduction steps mentioned in issue 507316 should not crash
     chrome.
     Unit test added to pdfium.
     Run pdfium_embeddertests.exe.

Review URL: https://codereview.chromium.org/1312313006 .

2 files changed, 26 insertions, 8 deletions

diff --git a/fpdfsdk/src/fpdfformfill_embeddertest.cpp b/fpdfsdk/src/fpdfformfill_embeddertest.cpp
index 6baad11531..56710b9f83 100644
--- a/fpdfsdk/src/fpdfformfill_embeddertest.cpp
+++ b/fpdfsdk/src/fpdfformfill_embeddertest.cpp
@@ -40,6 +40,18 @@ TEST_F(FPDFFormFillEmbeddertest, BUG_487928) {
   UnloadPage(page);
 }
 
+TEST_F(FPDFFormFillEmbeddertest, BUG_507316) {
+  EmbedderTestTimerHandlingDelegate delegate;
+  SetDelegate(&delegate);
+
+  EXPECT_TRUE(OpenDocument("testing/resources/bug_507316.pdf"));
+  FPDF_PAGE page = LoadAndCachePage(2);
+  EXPECT_NE(nullptr, page);
+  DoOpenActions();
+  delegate.AdvanceTime(4000);
+  UnloadPage(page);
+}
+
 TEST_F(FPDFFormFillEmbeddertest, BUG_514690) {
   EXPECT_TRUE(OpenDocument("testing/resources/hello_world.pdf"));
   FPDF_PAGE page = LoadPage(0);
diff --git a/fpdfsdk/src/fsdk_mgr.cpp b/fpdfsdk/src/fsdk_mgr.cpp
index 3eca559285..9cbb9de4d9 100644
--- a/fpdfsdk/src/fsdk_mgr.cpp
+++ b/fpdfsdk/src/fsdk_mgr.cpp
@@ -634,16 +634,22 @@ CPDFSDK_PageView::CPDFSDK_PageView(CPDFSDK_Document* pSDKDoc, CPDF_Page* page)
 }
 
 CPDFSDK_PageView::~CPDFSDK_PageView() {
-  CPDFDoc_Environment* pEnv = m_pSDKDoc->GetEnv();
-  int nAnnotCount = m_fxAnnotArray.GetSize();
+  // if there is a focused annot on the page, we should kill the focus first.
+  if (CPDFSDK_Annot* focusedAnnot = m_pSDKDoc->GetFocusAnnot()) {
+    for (int i = 0, count = m_fxAnnotArray.GetSize(); i < count; i++) {
+      CPDFSDK_Annot* pAnnot = (CPDFSDK_Annot*)m_fxAnnotArray.GetAt(i);
+      if (pAnnot == focusedAnnot) {
+        KillFocusAnnot();
+        break;
+      }
+    }
+  }
 
-  for (int i = 0; i < nAnnotCount; i++) {
+  CPDFDoc_Environment* pEnv = m_pSDKDoc->GetEnv();
+  CPDFSDK_AnnotHandlerMgr* pAnnotHandlerMgr = pEnv->GetAnnotHandlerMgr();
+  ASSERT(pAnnotHandlerMgr);
+  for (int i = 0, count = m_fxAnnotArray.GetSize(); i < count; i++) {
     CPDFSDK_Annot* pAnnot = (CPDFSDK_Annot*)m_fxAnnotArray.GetAt(i);
-    // if there is a focused annot on the page, we should kill the focus first.
-    if (pAnnot == m_pSDKDoc->GetFocusAnnot())
-      KillFocusAnnot();
-    CPDFSDK_AnnotHandlerMgr* pAnnotHandlerMgr = pEnv->GetAnnotHandlerMgr();
-    ASSERT(pAnnotHandlerMgr);
     pAnnotHandlerMgr->ReleaseAnnot(pAnnot);
   }
   m_fxAnnotArray.RemoveAll();