A new boolean on XModuleSystem that determines whether to allow execution of untrusted unsandboxed code.

common/lib/capa/capa/responsetypes.py

@@ -502,6 +502,10 @@ class JavascriptResponse(LoncapaResponse):
         return tmp_env
 
     def call_node(self, args):
+        # Node.js code is un-sandboxed. If the XModuleSystem says we aren't
+        # allowed to run unsafe code, then stop now.
+        if not self.system.can_execute_unsafe_code:
+            raise LoncapaProblemError("Execution of unsafe Javascript code is not allowed.")
 
         subprocess_args = ["node"]
         subprocess_args.extend(args)

common/lib/capa/capa/tests/__init__.py

@@ -40,6 +40,7 @@ def test_system():
         node_path=os.environ.get("NODE_PATH", "/usr/local/lib/node_modules"),
         anonymous_student_id='student',
         cache=None,
+        can_execute_unsafe_code=False,
     )
     return the_system
 

common/lib/capa/capa/tests/test_responsetypes.py

@@ -12,7 +12,7 @@ import textwrap
 import mock
 import textwrap
 
-from . import new_loncapa_problem
+from . import new_loncapa_problem, test_system
 
 from capa.responsetypes import LoncapaProblemError, \
     StudentInputError, ResponseError
@@ -30,9 +30,9 @@ class ResponseTest(unittest.TestCase):
         if self.xml_factory_class:
             self.xml_factory = self.xml_factory_class()
 
-    def build_problem(self, **kwargs):
+    def build_problem(self, system=None, **kwargs):
         xml = self.xml_factory.build_xml(**kwargs)
-        return new_loncapa_problem(xml)
+        return new_loncapa_problem(xml, system=system)
 
     def assert_grade(self, problem, submission, expected_correctness, msg=None):
         input_dict = {'1_2_1': submission}
@@ -746,16 +746,37 @@ class JavascriptResponseTest(ResponseTest):
         coffee_file_path = os.path.dirname(__file__) + "/test_files/js/*.coffee"
         os.system("coffee -c %s" % (coffee_file_path))
 
-        problem = self.build_problem(generator_src="test_problem_generator.js",
-                                     grader_src="test_problem_grader.js",
-                                     display_class="TestProblemDisplay",
-                                     display_src="test_problem_display.js",
-                                     param_dict={'value': '4'})
+        system = test_system()
+        system.can_execute_unsafe_code = True
+        problem = self.build_problem(
+            system=system,
+            generator_src="test_problem_generator.js",
+            grader_src="test_problem_grader.js",
+            display_class="TestProblemDisplay",
+            display_src="test_problem_display.js",
+            param_dict={'value': '4'},
+        )
 
         # Test that we get graded correctly
         self.assert_grade(problem, json.dumps({0: 4}), "correct")
         self.assert_grade(problem, json.dumps({0: 5}), "incorrect")
 
+    def test_cant_execute_javascript(self):
+        # If the system says to disallow unsafe code execution, then making
+        # this problem will raise an exception.
+        system = test_system()
+        system.can_execute_unsafe_code = False
+
+        with self.assertRaises(LoncapaProblemError):
+            problem = self.build_problem(
+                system=system,
+                generator_src="test_problem_generator.js",
+                grader_src="test_problem_grader.js",
+                display_class="TestProblemDisplay",
+                display_src="test_problem_display.js",
+                param_dict={'value': '4'},
+            )
+
 
 class NumericalResponseTest(ResponseTest):
     from response_xml_factory import NumericalResponseXMLFactory

common/lib/xmodule/xmodule/x_module.py

@@ -702,6 +702,7 @@ class ModuleSystem(object):
                  open_ended_grading_interface=None,
                  s3_interface=None,
                  cache=None,
+                 can_execute_unsafe_code=False,
                 ):
         '''
         Create a closure around the system environment.
@@ -749,6 +750,9 @@ class ModuleSystem(object):
             .get(key) returns an object from the cache or None.
             .set(key, value, timeout_secs=None) stores a value in the cache with a timeout.
 
+        can_execute_unsafe_code - A boolean, whether or not to allow the execution
+            of unsafe, unsandboxed code.
+
         '''
         self.ajax_url = ajax_url
         self.xqueue = xqueue
@@ -774,6 +778,7 @@ class ModuleSystem(object):
         self.s3_interface = s3_interface
 
         self.cache = cache or DoNothingCache()
+        self.can_execute_unsafe_code = can_execute_unsafe_code
 
     def get(self, attr):
         '''	provide uniform access to attributes (like etree).'''