Add some limit checks to ReadSharedObjHintTable().

core/fpdfapi/fpdf_parser/cpdf_hint_tables.cpp

Index: core/fpdfapi/fpdf_parser/cpdf_hint_tables.cpp
diff --git a/core/fpdfapi/fpdf_parser/cpdf_hint_tables.cpp b/core/fpdfapi/fpdf_parser/cpdf_hint_tables.cpp
index 4363d3924c9054b7e502efc5ce8f93a1af84b2c2..fd8765a2d210aad572635feb1346fa53c72478c6 100644
--- a/core/fpdfapi/fpdf_parser/cpdf_hint_tables.cpp
+++ b/core/fpdfapi/fpdf_parser/cpdf_hint_tables.cpp
@@ -278,6 +278,12 @@ bool CPDF_HintTables::ReadSharedObjHintTable(CFX_BitStream* hStream,
   // greatest and least length of a shared object group, in bytes.
   uint32_t dwDeltaGroupLen = hStream->GetBits(16);
 
+  if (dwFirstSharedObjNum >= CPDF_Parser::kMaxObjectNumber ||
+      m_nFirstPageSharedObjs >= CPDF_Parser::kMaxObjectNumber ||
+      dwSharedObjTotal >= CPDF_Parser::kMaxObjectNumber) {
+    return false;
+  }
+
   int nFirstPageObjNum = GetFirstPageObjectNumber();
   if (nFirstPageObjNum < 0)
     return false;