Add a simple check for V4 cross reference table

Some unknown software generates cross reference table with the
claimed object numbers are all off by one. Add a simple verification
function to detect this scenario, thus have a chance to rebuild
the correct cross reference table.

To avoid unnecessary checks and potiential performance hit, we only
check for the very first non free entry.

BUG=602650

Review URL: https://codereview.chromium.org/1910063004

1 files changed, 3 insertions, 0 deletions

diff --git a/core/fpdfapi/fpdf_parser/include/cpdf_parser.h b/core/fpdfapi/fpdf_parser/include/cpdf_parser.h
index 5331ccafb1..48511e9263 100644
--- a/core/fpdfapi/fpdf_parser/include/cpdf_parser.h
+++ b/core/fpdfapi/fpdf_parser/include/cpdf_parser.h
@@ -114,6 +114,9 @@ class CPDF_Parser {
   FX_BOOL IsLinearizedFile(IFX_FileRead* pFileAccess, uint32_t offset);
   void SetEncryptDictionary(CPDF_Dictionary* pDict);
   void ShrinkObjectMap(uint32_t size);
+  // A simple check whether the cross reference table matches with
+  // the objects.
+  bool VerifyCrossRefV4();
 
   CPDF_Document* m_pDocument;
   std::unique_ptr<CPDF_SyntaxParser> m_pSyntax;