Null CPDF_CountedObj::m_pObj prior to deletion

This gives additional protection in case of re-entry. Also
make CFX_CountRef more robust in face of errors.

BUG=649229

Review-Url: https://codereview.chromium.org/2364673002

3 files changed, 12 insertions, 3 deletions

diff --git a/core/fpdfapi/fpdf_page/cpdf_countedobject.h b/core/fpdfapi/fpdf_page/cpdf_countedobject.h
index e7f4ab6af0..c61e024589 100644
--- a/core/fpdfapi/fpdf_page/cpdf_countedobject.h
+++ b/core/fpdfapi/fpdf_page/cpdf_countedobject.h
@@ -20,8 +20,10 @@ class CPDF_CountedObject {
     m_pObj = ptr;
   }
   void clear() {  // Now you're all weak ptrs ...
-    delete m_pObj;
+    // Guard against accidental re-entry.
+    T* pObj = m_pObj;
     m_pObj = nullptr;
+    delete pObj;
   }
   T* get() const { return m_pObj; }
   T* AddRef() {
diff --git a/core/fxcrt/cfx_string_data_template.h b/core/fxcrt/cfx_string_data_template.h
index 225020a7dd..5f7bfa1f83 100644
--- a/core/fxcrt/cfx_string_data_template.h
+++ b/core/fxcrt/cfx_string_data_template.h
@@ -85,7 +85,7 @@ class CFX_StringDataTemplate {
   // Since the count increments with each new pointer, the largest value is
   // the number of pointers that can fit into the address space. The size of
   // the address space itself is a good upper bound on it.
-  intptr_t m_nRefs;  // Would prefer ssize_t, but no windows support.
+  intptr_t m_nRefs;
 
   // |FX_STRSIZE| is currently typedef'd as |int|.
   // TODO(palmer): It should be a |size_t|, or at least unsigned.
diff --git a/core/fxcrt/include/cfx_count_ref.h b/core/fxcrt/include/cfx_count_ref.h
index d709efb67c..a879967b28 100644
--- a/core/fxcrt/include/cfx_count_ref.h
+++ b/core/fxcrt/include/cfx_count_ref.h
@@ -56,15 +56,22 @@ class CFX_CountRef {
     CountedObj(Args... params) : ObjClass(params...), m_RefCount(0) {}
 
     CountedObj(const CountedObj& src) : ObjClass(src), m_RefCount(0) {}
+    ~CountedObj() { m_RefCount = 0; }
 
     bool HasOneRef() const { return m_RefCount == 1; }
     void Retain() { m_RefCount++; }
     void Release() {
-      if (--m_RefCount <= 0)
+      ASSERT(m_RefCount);
+      if (--m_RefCount == 0)
         delete this;
     }
 
    private:
+    // To ensure ref counts do not overflow, consider the worst possible case:
+    // the entire address space contains nothing but pointers to this object.
+    // Since the count increments with each new pointer, the largest value is
+    // the number of pointers that can fit into the address space. The size of
+    // the address space itself is a good upper bound on it.
     intptr_t m_RefCount;
   };