Fix blank page issues caused by too strict check

Before this fix, PDF parser aborts the parsering process when detecting an error.
For this case, PDF parser just gives up parsering when it detects that the length of
image stream is incorrect. The solution to this case is to find the tag "endstream"
and "endobj" to calculate the length rather than aborting the parsering process.

BUG=433339
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/743263002

(cherry picked from commit ef619d0562b39f30943cfdc4985a0df233d00e42)

Review URL: https://codereview.chromium.org/776833002

1 files changed, 6 insertions, 9 deletions

diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
index e9c0fdd227..85992a83e3 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
@@ -2435,16 +2435,13 @@ CPDF_Stream* CPDF_SyntaxParser::ReadStream(CPDF_Dictionary* pDict, PARSE_CONTEXT
         pContext->m_DataStart = m_Pos;
     }
 
-    base::CheckedNumeric<FX_FILESIZE> pos = m_Pos;
-    pos += len;
-    if (pos.IsValid() && pos.ValueOrDie() < m_FileLen) {
-        m_Pos = pos.ValueOrDie();
-    } else {
-        return NULL;
-    }
-
     CPDF_CryptoHandler* pCryptoHandler = objnum == (FX_DWORD)m_MetadataObjnum ? NULL : m_pCryptoHandler;
     if (pCryptoHandler == NULL) {
+        base::CheckedNumeric<FX_FILESIZE> pos = m_Pos;
+        pos += len;
+        if (pos.IsValid() && pos.ValueOrDie() < m_FileLen) {
+            m_Pos = pos.ValueOrDie();
+        }
         GetNextWord();
         if (m_WordSize < 9 || FXSYS_memcmp32(m_WordBuffer, "endstream", 9)) {
             m_Pos = StreamStartPos;
@@ -2475,8 +2472,8 @@ CPDF_Stream* CPDF_SyntaxParser::ReadStream(CPDF_Dictionary* pDict, PARSE_CONTEXT
                 }
             }
         }
+        m_Pos = StreamStartPos;
     }
-    m_Pos = StreamStartPos;
     CPDF_Stream* pStream;
 #if defined(_FPDFAPI_MINI_) && !defined(_FXCORE_FEATURE_ALL_)
     pStream = FX_NEW CPDF_Stream(m_pFileAccess, pCryptoHandler, m_HeaderOffset + m_Pos, len, pDict, gennum);