Perform better input checks in early steps of parser.

core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp

Index: core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
index e0fd3bfaeecea13e1b023d68982f3d35897ff2b9..d2a02d0177d686878bbd6f9460b292d3b09e566c 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
@@ -158,10 +158,17 @@ FX_DWORD CPDF_Parser::StartParse(IFX_FileRead* pFileAccess, FX_BOOL bReParse, FX
     }
     m_Syntax.InitParser(pFileAccess, offset);
     FX_BYTE ch;
-    m_Syntax.GetCharAt(5, ch);
+    if (!m_Syntax.GetCharAt(5, ch) || ch < '0' || ch > '9') {

[jun_fang, 2014/08/25 19:44:04]

This is used to parse file version which is not important information. Even it's
invalid, we shouldn't need to block the further parsing. So it's better to keep
it no change. 

[Tom Sepez, 2014/08/25 20:05:32]

Ok.  I'll keep going but ingore out-of-range values, then.

+        return PDFPARSE_ERROR_FORMAT;
+    }
     m_FileVersion = (ch - '0') * 10;
-    m_Syntax.GetCharAt(7, ch);
+    if (!m_Syntax.GetCharAt(7, ch) || ch < '0' || ch > '9') {
+        return PDFPARSE_ERROR_FORMAT;
+    }
     m_FileVersion += ch - '0';
+    if (m_Syntax.m_FileLen <  m_Syntax.m_HeaderOffset + 9) {
+        return PDFPARSE_ERROR_FORMAT;
+    }
     m_Syntax.RestorePos(m_Syntax.m_FileLen - m_Syntax.m_HeaderOffset - 9);
     if (!bReParse) {
         m_pDocument = FX_NEW CPDF_Document(this);