[Backport] CVE-2023-1530: Use after free in PDF (1/2)

Manual backport of patch originally reviewed on
https://pdfium-review.googlesource.com/c/pdfium/+/104397:
Observe CPWL_* object destruction across CPDFSDK_Widget methods

This is a simple fix to stop the symptoms while we investigate
how to avoid mutations at these points in the first place.

-- fix some nearby braces and annoying blank lines while at it.

Bug: chromium:1419831
Change-Id: I20c38806b91c7c0c9016bb1b567a04ce319243d8
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/104397
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-on: https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/469851
Reviewed-by: Michal Klocek <michal.klocek@qt.io>

3 files changed, 34 insertions, 20 deletions

diff --git a/chromium/third_party/pdfium/fpdfsdk/formfiller/cffl_checkbox.cpp b/chromium/third_party/pdfium/fpdfsdk/formfiller/cffl_checkbox.cpp
index c8f114896a1..3647bd3dbc4 100644
--- a/chromium/third_party/pdfium/fpdfsdk/formfiller/cffl_checkbox.cpp
+++ b/chromium/third_party/pdfium/fpdfsdk/formfiller/cffl_checkbox.cpp
@@ -64,8 +64,12 @@ bool CFFL_CheckBox::OnChar(CPDFSDK_Annot* pAnnot,
 
       CPWL_CheckBox* pWnd = GetCheckBox(pPageView, true);
       if (pWnd && !pWnd->IsReadOnly()) {
+        ObservedPtr<CPWL_CheckBox> pObservedBox(pWnd);
         CPDFSDK_Widget* pWidget = ToCPDFSDKWidget(pAnnot);
-        pWnd->SetCheck(!pWidget->IsChecked());
+        const bool is_checked = pWidget->IsChecked();
+        if (pObservedBox) {
+          pObservedBox->SetCheck(!is_checked);
+        }
       }
 
       return CommitData(pPageView, nFlags);
@@ -86,8 +90,12 @@ bool CFFL_CheckBox::OnLButtonUp(CPDFSDK_PageView* pPageView,
 
   CPWL_CheckBox* pWnd = GetCheckBox(pPageView, true);
   if (pWnd) {
+    ObservedPtr<CPWL_CheckBox> pObservedBox(pWnd);
     CPDFSDK_Widget* pWidget = ToCPDFSDKWidget(pAnnot);
-    pWnd->SetCheck(!pWidget->IsChecked());
+    const bool is_checked = pWidget->IsChecked();
+    if (pObservedBox) {
+      pObservedBox->SetCheck(!is_checked);
+    }
   }
 
   return CommitData(pPageView, nFlags);
diff --git a/chromium/third_party/pdfium/fpdfsdk/formfiller/cffl_listbox.cpp b/chromium/third_party/pdfium/fpdfsdk/formfiller/cffl_listbox.cpp
index 0cbc20a213c..c35f1485d51 100644
--- a/chromium/third_party/pdfium/fpdfsdk/formfiller/cffl_listbox.cpp
+++ b/chromium/third_party/pdfium/fpdfsdk/formfiller/cffl_listbox.cpp
@@ -110,7 +110,11 @@ void CFFL_ListBox::SaveData(CPDFSDK_PageView* pPageView) {
     return;
 
   int32_t nNewTopIndex = pListBox->GetTopVisibleIndex();
+  ObservedPtr<CPWL_ListBox> observed_box(pListBox);
   m_pWidget->ClearSelection(NotificationOption::kDoNotNotify);
+  if (!observed_box) {
+    return;
+  }
   if (m_pWidget->GetFieldFlags() & pdfium::form_flags::kChoiceMultiSelect) {
     for (int32_t i = 0, sz = pListBox->GetCount(); i < sz; i++) {
       if (pListBox->IsItemSelected(i)) {
@@ -125,17 +129,17 @@ void CFFL_ListBox::SaveData(CPDFSDK_PageView* pPageView) {
   ObservedPtr<CPDFSDK_Widget> observed_widget(m_pWidget.Get());
   ObservedPtr<CFFL_ListBox> observed_this(this);
   m_pWidget->SetTopVisibleIndex(nNewTopIndex);
-  if (!observed_widget)
+  if (!observed_widget) {
     return;
-
+  }
   m_pWidget->ResetFieldAppearance();
-  if (!observed_widget)
+  if (!observed_widget) {
     return;
-
+  }
   m_pWidget->UpdateField();
-  if (!observed_widget || !observed_this)
+  if (!observed_widget || !observed_this) {
     return;
-
+  }
   SetChangeMark();
 }
 
diff --git a/chromium/third_party/pdfium/fpdfsdk/formfiller/cffl_textfield.cpp b/chromium/third_party/pdfium/fpdfsdk/formfiller/cffl_textfield.cpp
index 93ec9fe1e72..85402d45d23 100644
--- a/chromium/third_party/pdfium/fpdfsdk/formfiller/cffl_textfield.cpp
+++ b/chromium/third_party/pdfium/fpdfsdk/formfiller/cffl_textfield.cpp
@@ -145,26 +145,30 @@ bool CFFL_TextField::IsDataChanged(CPDFSDK_PageView* pPageView) {
 }
 
 void CFFL_TextField::SaveData(CPDFSDK_PageView* pPageView) {
-  CPWL_Edit* pWnd = GetEdit(pPageView, false);
-  if (!pWnd)
+  ObservedPtr<CPWL_Edit> observed_edit(GetEdit(pPageView, false));
+  if (!observed_edit) {
     return;
-
+  }
   WideString sOldValue = m_pWidget->GetValue();
-  WideString sNewValue = pWnd->GetText();
+  if (!observed_edit) {
+    return;
+  }
+
+  WideString sNewValue = observed_edit->GetText();
   ObservedPtr<CPDFSDK_Widget> observed_widget(m_pWidget.Get());
   ObservedPtr<CFFL_TextField> observed_this(this);
   m_pWidget->SetValue(sNewValue, NotificationOption::kDoNotNotify);
-  if (!observed_widget)
+  if (!observed_widget) {
     return;
-
+  }
   m_pWidget->ResetFieldAppearance();
-  if (!observed_widget)
+  if (!observed_widget) {
     return;
-
+  }
   m_pWidget->UpdateField();
-  if (!observed_widget || !observed_this)
+  if (!observed_widget || !observed_this) {
     return;
-
+  }
   SetChangeMark();
 }
 
@@ -175,9 +179,7 @@ void CFFL_TextField::GetActionData(CPDFSDK_PageView* pPageView,
     case CPDF_AAction::kKeyStroke:
       if (CPWL_Edit* pWnd = GetEdit(pPageView, false)) {
         fa.bFieldFull = pWnd->IsTextFull();
-
         fa.sValue = pWnd->GetText();
-
         if (fa.bFieldFull) {
           fa.sChange.clear();
           fa.sChangeEx.clear();