Fix a potential UAF with FPDFAvail_IsLinearized().

core/fpdfapi/fpdf_parser/cpdf_data_avail.cpp

 // Copyright 2016 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "core/fpdfapi/fpdf_parser/include/ipdf_data_avail.h"
 
 #include "core/fpdfapi/fpdf_parser/cpdf_data_avail.h"
 #include "core/fpdfapi/fpdf_parser/fpdf_parser_utility.h"
@@ skipping 833 matching lines @@
   m_syntaxParser.InitParser(file.get(), offset);
   m_syntaxParser.RestorePos(m_syntaxParser.m_HeaderOffset + 9);
 
   bool bNumber;
   CFX_ByteString wordObjNum = m_syntaxParser.GetNextWord(&bNumber);
   if (!bNumber)
     return FALSE;
 
   uint32_t objnum = FXSYS_atoui(wordObjNum.c_str());
   if (m_pLinearized) {
+    m_pHintTables.reset();

[Wei Li, 2016/05/11 00:26:25]

Will we lose hint stream info then? Will we still need that info for subsequent
loading?

[Lei Zhang, 2016/05/11 01:16:21]

Yes, and that's not optimal. See patch set 2 - use the cached result instead.
There's no point in reparsing the header again, right?

     m_pLinearized->Release();
-    m_pLinearized = nullptr;
   }
 
   m_pLinearized =
       ParseIndirectObjectAt(m_syntaxParser.m_HeaderOffset + 9, objnum);
   if (!m_pLinearized)
     return FALSE;
 
   CPDF_Dictionary* pDict = m_pLinearized->GetDict();
-  if (pDict && pDict->GetObjectBy("Linearized")) {
-    CPDF_Object* pLen = pDict->GetObjectBy("L");
-    if (!pLen)
-      return FALSE;
+  if (!pDict || !pDict->GetObjectBy("Linearized"))
+    return FALSE;
 
-    if ((FX_FILESIZE)pLen->GetInteger() != m_pFileRead->GetSize())
-      return FALSE;
+  CPDF_Object* pLen = pDict->GetObjectBy("L");
+  if (!pLen)
+    return FALSE;
 
-    m_bLinearized = TRUE;
+  if ((FX_FILESIZE)pLen->GetInteger() != m_pFileRead->GetSize())
+    return FALSE;
 
-    if (CPDF_Number* pNo = ToNumber(pDict->GetObjectBy("P")))
-      m_dwFirstPageNo = pNo->GetInteger();
+  m_bLinearized = TRUE;
 
-    return TRUE;
-  }
-  return FALSE;
+  if (CPDF_Number* pNo = ToNumber(pDict->GetObjectBy("P")))
+    m_dwFirstPageNo = pNo->GetInteger();
+
+  return TRUE;
 }
 
 FX_BOOL CPDF_DataAvail::CheckEnd(IPDF_DataAvail::DownloadHints* pHints) {
   uint32_t req_pos = (uint32_t)(m_dwFileLen > 1024 ? m_dwFileLen - 1024 : 0);
   uint32_t dwSize = (uint32_t)(m_dwFileLen - req_pos);
 
   if (m_pFileAvail->IsDataAvail(req_pos, dwSize)) {
     uint8_t buffer[1024];
     m_pFileRead->ReadBlock(buffer, req_pos, dwSize);
 
@@ skipping 942 matching lines @@
   return FormAvailable;
 }
 
 CPDF_DataAvail::PageNode::PageNode() : m_type(PDF_PAGENODE_UNKNOWN) {}
 
 CPDF_DataAvail::PageNode::~PageNode() {
   for (int32_t i = 0; i < m_childNode.GetSize(); ++i)
     delete m_childNode[i];
   m_childNode.RemoveAll();
 }