Avoid resolving arguments to R

When checking two objects preceding R while parsing, ensure that the
objects are direct. This avoids stuff like 1 0 obj containing 1 0 R 0 R
from causing an infinite loop in object resolution.

ChangeLog

@@ -1,3 +1,11 @@
+2015-02-21  Jay Berkenbilt  <ejb@ql.org>
+
+	* Ensure that arguments to "R" when parsing the file are direct
+	objects before trying to resolve them. This prevents specially
+	crafted files from causing qpdf to crash with a stack overflow.
+	Thanks to Gynvael Coldwind and Mateusz Jurczyk of the Google
+	Security Team for providing a sample file with this problem.
+
 2014-12-01  Jay Berkenbilt  <ejb@ql.org>
 
 	* Some broken PDF files lack the required /Type key for /Page and

libqpdf/QPDFObjectHandle.cc

@@ -966,7 +966,9 @@ QPDFObjectHandle::parseInternal(PointerHolder<InputSource> input,
 		std::string const& value = token.getValue();
 		if ((value == "R") && (in_array || in_dictionary) &&
 		    (olist.size() >= 2) &&
+                    (! olist.at(olist.size() - 1).isIndirect()) &&
 		    (olist.at(olist.size() - 1).isInteger()) &&
+                    (! olist.at(olist.size() - 2).isIndirect()) &&
 		    (olist.at(olist.size() - 2).isInteger()))
 		{
                     if (context == 0)

qpdf/qtest/qpdf.test

@@ -199,7 +199,7 @@ $td->runtest("remove page we don't have",
 show_ntests();
 # ----------
 $td->notify("--- Miscellaneous Tests ---");
-$n_tests += 74;
+$n_tests += 75;
 
 $td->runtest("qpdf version",
 	     {$td->COMMAND => "qpdf --version"},
@@ -562,6 +562,10 @@ $td->runtest("no type key for page nodes",
              {$td->COMMAND => "qpdf --check no-pages-types.pdf"},
              {$td->FILE => "no-pages-types.out", $td->EXIT_STATUS => 0},
              $td->NORMALIZE_NEWLINES);
+$td->runtest("ensure arguments to R are direct",
+             {$td->COMMAND => "qpdf --check indirect-r-arg.pdf"},
+             {$td->FILE => "indirect-r-arg.out", $td->EXIT_STATUS => 2},
+             $td->NORMALIZE_NEWLINES);
 
 show_ntests();
 # ----------

qpdf/qtest/qpdf/indirect-r-arg.out

@@ -0,0 +1 @@
+indirect-r-arg.pdf (file position 76): unknown token while reading object (R)

qpdf/qtest/qpdf/indirect-r-arg.pdf

@@ -0,0 +1,102 @@
+%PDF-1.3
+%¿÷¢þ
+%QDF-1.0
+
+%% Original object ID: 1 0
+1 0 obj
+<<
+  /X 1 0 R 0 R
+  /Pages 2 0 R
+  /Type /Catalog
+>>
+endobj
+
+%% Original object ID: 2 0
+2 0 obj
+<<
+  /Count 1
+  /Kids [
+    3 0 R
+  ]
+  /Type /Pages
+>>
+endobj
+
+%% Page 1
+%% Original object ID: 3 0
+3 0 obj
+<<
+  /Contents 4 0 R
+  /MediaBox [
+    0
+    0
+    612
+    792
+  ]
+  /Parent 2 0 R
+  /Resources <<
+    /Font <<
+      /F1 6 0 R
+    >>
+    /ProcSet 7 0 R
+  >>
+  /Type /Page
+>>
+endobj
+
+%% Contents for page 1
+%% Original object ID: 4 0
+4 0 obj
+<<
+  /Length 5 0 R
+>>
+stream
+BT
+  /F1 24 Tf
+  72 720 Td
+  (Potato) Tj
+ET
+endstream
+endobj
+
+5 0 obj
+44
+endobj
+
+%% Original object ID: 6 0
+6 0 obj
+<<
+  /BaseFont /Helvetica
+  /Encoding /WinAnsiEncoding
+  /Name /F1
+  /Subtype /Type1
+  /Type /Font
+>>
+endobj
+
+%% Original object ID: 5 0
+7 0 obj
+[
+  /PDF
+  /Text
+]
+endobj
+
+xref
+0 8
+0000000000 65535 f 
+0000000052 00000 n 
+0000000148 00000 n 
+0000000257 00000 n 
+0000000499 00000 n 
+0000000598 00000 n 
+0000000644 00000 n 
+0000000789 00000 n 
+trailer <<
+  /Root 1 0 R
+  /Size 8
+  /ID [<9e2756c6254602d0b896148e97ee7414><9e2756c6254602d0b896148e97ee7414>]
+>>
+startxref
+824
+%%EOF