Protect against coding error of re-entrant parsing

include/qpdf/QPDF.hh

@@ -657,6 +657,31 @@ class QPDF
     };
     friend class Warner;
 
+    // ParseGuard class allows QPDFObjectHandle to detect re-entrant
+    // resolution
+    class ParseGuard
+    {
+	friend class QPDFObjectHandle;
+      private:
+        ParseGuard(QPDF* qpdf) :
+            qpdf(qpdf)
+        {
+            if (qpdf)
+            {
+                qpdf->inParse(true);
+            }
+        }
+        ~ParseGuard()
+        {
+            if (qpdf)
+            {
+                qpdf->inParse(false);
+            }
+        }
+        QPDF* qpdf;
+    };
+    friend class ParseGuard;
+
     // Pipe class is restricted to QPDF_Stream
     class Pipe
     {
@@ -816,6 +841,7 @@ class QPDF
     friend class ResolveRecorder;
 
     void parse(char const* password);
+    void inParse(bool);
     void warn(QPDFExc const& e);
     void setTrailer(QPDFObjectHandle obj);
     void read_xref(qpdf_offset_t offset);
@@ -1352,6 +1378,7 @@ class QPDF
         bool reconstructed_xref;
         bool fixed_dangling_refs;
         bool immediate_copy_from;
+        bool in_parse;
 
         // Linearization data
         qpdf_offset_t first_xref_item_offset; // actual value from file

libqpdf/QPDF.cc

@@ -150,6 +150,7 @@ QPDF::Members::Members() :
     reconstructed_xref(false),
     fixed_dangling_refs(false),
     immediate_copy_from(false),
+    in_parse(false),
     first_xref_item_offset(0),
     uncompressed_after_compressed(false)
 {
@@ -416,6 +417,20 @@ QPDF::parse(char const* password)
     findAttachmentStreams();
 }
 
+void
+QPDF::inParse(bool v)
+{
+    if (this->m->in_parse == v)
+    {
+        // This happens of QPDFObjectHandle::parseInternal tries to
+        // resolve an indirect object while it is parsing.
+        throw std::logic_error(
+            "QPDF: re-entrant parsing detected. This is a qpdf bug."
+            " Please report at https://github.com/qpdf/qpdf/issues.");
+    }
+    this->m->in_parse = v;
+}
+
 void
 QPDF::warn(QPDFExc const& e)
 {

libqpdf/QPDFObjectHandle.cc

@@ -1714,7 +1714,11 @@ QPDFObjectHandle::parseInternal(PointerHolder<InputSource> input,
     // This method must take care not to resolve any objects. Don't
     // check the type of any object without first ensuring that it is
     // a direct object. Otherwise, doing so may have the side effect
-    // of reading the object and changing the file pointer.
+    // of reading the object and changing the file pointer. If you do
+    // this, it will cause a logic error to be thrown from
+    // QPDF::inParse().
+
+    QPDF::ParseGuard pg(context);
 
     empty = false;