Explicitly check root dictionary type

Very badly corrupted files may not have a retrievable root dictionary.
Handle that as a special case so that a more helpful error message can
be provided.

1 files changed, 8 insertions, 1 deletions

diff --git a/libqpdf/QPDF.cc b/libqpdf/QPDF.cc
index b5c1212c..4d5bf67f 100644
--- a/libqpdf/QPDF.cc
+++ b/libqpdf/QPDF.cc
@@ -2028,7 +2028,14 @@ QPDF::getTrailer()
 QPDFObjectHandle
 QPDF::getRoot()
 {
-    return this->trailer.getKey("/Root");
+    QPDFObjectHandle root = this->trailer.getKey("/Root");
+    if (! root.isDictionary())
+    {
+        throw QPDFExc(qpdf_e_damaged_pdf, file->getName(),
+                      "", file->getLastOffset(),
+                      "unable to find /Root dictionary");
+    }
+    return root;
 }
 
 void