Limit depth of nesting in direct objects (fixes #202)

This fixes CVE-2018-9918.
qpdf · Apr 15, 2018 · b4d6cf6 · b4d6cf6
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diff --git a/ChangeLog b/ChangeLog
@@ -1,3 +1,8 @@
+2018-04-15  Jay Berkenbilt  <ejb@ql.org>
+
+	* Arbitrarily limit the depth of data structures represented by
+	direct object. This is CVE-2018-9918. Fixes #202.
+
 2018-03-06  Jay Berkenbilt  <ejb@ql.org>
 
 	* 8.0.2: release

diff --git a/libqpdf/QPDFObjectHandle.cc b/libqpdf/QPDFObjectHandle.cc
@@ -1487,12 +1487,26 @@ QPDFObjectHandle::parseInternal(PointerHolder<InputSource> input,
 
 	  case QPDFTokenizer::tt_array_open:
 	  case QPDFTokenizer::tt_dict_open:
-            olist_stack.push_back(std::vector<QPDFObjectHandle>());
-            state = st_start;
-            offset_stack.push_back(input->tell());
-            state_stack.push_back(
-                (token.getType() == QPDFTokenizer::tt_array_open) ?
-                st_array : st_dictionary);
+            if (olist_stack.size() > 500)
+            {
+		QTC::TC("qpdf", "QPDFObjectHandle too deep");
+                warn(context,
+                     QPDFExc(qpdf_e_damaged_pdf, input->getName(),
+                             object_description,
+                             input->getLastOffset(),
+                             "ignoring excessively deeply nested data structure"));
+                object = newNull();
+                state = st_top;
+            }
+            else
+            {
+                olist_stack.push_back(std::vector<QPDFObjectHandle>());
+                state = st_start;
+                offset_stack.push_back(input->tell());
+                state_stack.push_back(
+                    (token.getType() == QPDFTokenizer::tt_array_open) ?
+                    st_array : st_dictionary);
+            }
 	    break;
 
 	  case QPDFTokenizer::tt_bool:

diff --git a/qpdf/qpdf.testcov b/qpdf/qpdf.testcov
@@ -335,3 +335,4 @@ QPDFObjectHandle numeric non-numeric 0
 QPDFObjectHandle erase array bounds 0
 qpdf-c called qpdf_check_pdf 0
 QPDF xref loop 0
+QPDFObjectHandle too deep 0
diff --git a/qpdf/qtest/qpdf.test b/qpdf/qtest/qpdf.test
@@ -236,6 +236,7 @@ my @bug_tests = (
     ["148", "free memory on bad flate", 2],
     ["149", "xref prev pointer loop", 3],
     ["150", "integer overflow", 2],
+    ["202", "even more deeply nested dictionary", 2],
     );
 $n_tests += scalar(@bug_tests);
 foreach my $d (@bug_tests)

diff --git a/qpdf/qtest/qpdf/issue-146.out b/qpdf/qtest/qpdf/issue-146.out
@@ -1,7 +1,5 @@
 WARNING: issue-146.pdf: file is damaged
 WARNING: issue-146.pdf: can't find startxref
 WARNING: issue-146.pdf: Attempting to reconstruct cross-reference table
-WARNING: issue-146.pdf (trailer, offset 20728): unknown token while reading object; treating as string
-WARNING: issue-146.pdf (trailer, offset 20732): unexpected EOF
-WARNING: issue-146.pdf (trailer, offset 20732): parse error while reading object
+WARNING: issue-146.pdf (trailer, offset 695): ignoring excessively deeply nested data structure
 issue-146.pdf: unable to find trailer dictionary while recovering damaged file
diff --git a/qpdf/qtest/qpdf/issue-202.out b/qpdf/qtest/qpdf/issue-202.out
@@ -0,0 +1,5 @@
+WARNING: issue-202.pdf (trailer, offset 55770): ignoring excessively deeply nested data structure
+WARNING: issue-202.pdf: file is damaged
+WARNING: issue-202.pdf (offset 54769): expected trailer dictionary
+WARNING: issue-202.pdf: Attempting to reconstruct cross-reference table
+issue-202.pdf: unable to find trailer dictionary while recovering damaged file
diff --git a/qpdf/qtest/qpdf/issue-202.pdf b/qpdf/qtest/qpdf/issue-202.pdf