Based on the discussion at
https://bitbucket.org/cffi/cffi/issues/366/fix-known-small-but-needless-leak

--- cffi-1.10.0/c/lib_obj.c	2017-03-21 16:11:29.000000000 +0530
+++ cffi-1.10.0-new/c/lib_obj.c	2018-07-02 16:27:45.120352980 +0530
@@ -328,6 +328,12 @@ static PyObject *lib_build_and_cache_att
         }
         x = convert_to_object(data, ct);
         Py_DECREF(ct);
+
+        if (!(ct->ct_flags & CT_PRIMITIVE_ANY)) {
+            if (ct->ct_flags & (CT_POINTER|CT_FUNCTIONPTR)) {
+                PyMem_Free(data);
+            }
+        }
         break;
     }