Adding constraints around qemu-img calls

* All "qemu-img info" calls are now run under resource limitations
  that limit CPU time to 2 seconds and address space usage to 1 GB.
  This helps avoid any DoS attacks via malicious images.
* All "qemu-img convert" calls now specify the import format so that
  it does not have to be inferred by qemu-img.

SecurityImpact

Change-Id: Ib900bbc05cb9ccd90c6f56ccb4bf2006e30cdc80
Closes-Bug: #1449062
(cherry picked from commit 69a9b659fd)

glance/async/flows/base_import.py

@@ -30,6 +30,7 @@ from taskflow import retry
 from taskflow import task
 from taskflow.types import failure
 
+from glance.async import utils
 from glance.common import exception
 from glance.common.scripts.image_import import main as image_import
 from glance.common.scripts import utils as script_utils
@@ -154,6 +155,7 @@ class _ImportToFS(task.Task):
             # place that other tasks can consume as well.
             stdout, stderr = putils.trycmd('qemu-img', 'info',
                                            '--output=json', path,
+                                           prlimit=utils.QEMU_IMG_PROC_LIMITS,
                                            log_errors=putils.LOG_ALL_ERRORS)
         except OSError as exc:
             with excutils.save_and_reraise_exception():

glance/async/flows/convert.py

@@ -69,12 +69,23 @@ class _Convert(task.Task):
                 _Convert.conversion_missing_warned = True
             return
 
+        image_obj = self.image_repo.get(image_id)
+        src_format = image_obj.disk_format
+
         # TODO(flaper87): Check whether the image is in the desired
         # format already. Probably using `qemu-img` just like the
         # `Introspection` task.
+
+        # NOTE(hemanthm): We add '-f' parameter to the convert command here so
+        # that the image format need not be inferred by qemu utils. This
+        # shields us from being vulnerable to an attack vector described here
+        # https://bugs.launchpad.net/glance/+bug/1449062
+
         dest_path = os.path.join(CONF.task.work_dir, "%s.converted" % image_id)
-        stdout, stderr = putils.trycmd('qemu-img', 'convert', '-O',
-                                       conversion_format, file_path, dest_path,
+        stdout, stderr = putils.trycmd('qemu-img', 'convert',
+                                       '-f', src_format,
+                                       '-O', conversion_format,
+                                       file_path, dest_path,
                                        log_errors=putils.LOG_ALL_ERRORS)
 
         if stderr:

glance/async/flows/introspect.py

@@ -48,6 +48,7 @@ class _Introspect(utils.OptionalTask):
         try:
             stdout, stderr = putils.trycmd('qemu-img', 'info',
                                            '--output=json', file_path,
+                                           prlimit=utils.QEMU_IMG_PROC_LIMITS,
                                            log_errors=putils.LOG_ALL_ERRORS)
         except OSError as exc:
             # NOTE(flaper87): errno == 2 means the executable file

glance/async/utils.py

@@ -13,8 +13,10 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+from oslo_concurrency import processutils as putils
 from oslo_log import log as logging
 from oslo_utils import encodeutils
+from oslo_utils import units
 from taskflow import task
 
 from glance.i18n import _LW
@@ -22,6 +24,14 @@ from glance.i18n import _LW
 
 LOG = logging.getLogger(__name__)
 
+# NOTE(hemanthm): As reported in the bug #1449062, "qemu-img info" calls can
+# be exploited to craft DoS attacks by providing malicious input. The process
+# limits defined here are protections against such attacks. This essentially
+# limits the CPU time and address space used by the process that executes
+# "qemu-img info" command to 2 seconds and 1 GB respectively.
+QEMU_IMG_PROC_LIMITS = putils.ProcessLimits(cpu_time=2,
+                                            address_space=1 * units.Gi)
+
 
 class OptionalTask(task.Task):
 

glance/tests/unit/async/flows/test_convert.py

@@ -94,6 +94,12 @@ class TestImportTask(test_utils.BaseTestCase):
                 rm_mock.return_value = None
                 image_convert.execute(image, 'file:///test/path.raw')
 
+                # NOTE(hemanthm): Asserting that the source format is passed
+                # to qemu-utis to avoid inferring the image format. This
+                # shields us from an attack vector described at
+                # https://bugs.launchpad.net/glance/+bug/1449062/comments/72
+                self.assertIn('-f', exc_mock.call_args[0])
+
     def test_convert_revert_success(self):
         image_convert = convert._Convert(self.task.task_id,
                                          self.task_type,
@@ -178,3 +184,15 @@ class TestImportTask(test_utils.BaseTestCase):
                 self.assertEqual([], os.listdir(self.work_dir))
                 self.assertEqual('qcow2', image.disk_format)
                 self.assertEqual(10737418240, image.virtual_size)
+
+                # NOTE(hemanthm): Asserting that the source format is passed
+                # to qemu-utis to avoid inferring the image format when
+                # converting. This shields us from an attack vector described
+                # at https://bugs.launchpad.net/glance/+bug/1449062/comments/72
+                #
+                # A total of three calls will be made to 'execute': 'info',
+                # 'convert' and 'info' towards introspection, conversion and
+                # OVF packaging respectively. We care about the 'convert' call
+                # here, hence we fetch the 2nd set of args from the args list.
+                convert_call_args, _ = exc_mock.call_args_list[1]
+                self.assertIn('-f', convert_call_args)

glance/tests/unit/async/flows/test_import.py

@@ -27,6 +27,7 @@ from taskflow.types import failure
 
 import glance.async.flows.base_import as import_flow
 from glance.async import taskflow_executor
+from glance.async import utils as async_utils
 from glance.common.scripts.image_import import main as image_import
 from glance.common.scripts import utils as script_utils
 from glance.common import utils
@@ -86,6 +87,14 @@ class TestImportTask(test_utils.BaseTestCase):
                                                task_time_to_live=task_ttl,
                                                task_input=task_input)
 
+    def _assert_qemu_process_limits(self, exec_mock):
+        # NOTE(hemanthm): Assert that process limits are being applied
+        # on "qemu-img info" calls. See bug #1449062 for more details.
+        kw_args = exec_mock.call_args[1]
+        self.assertIn('prlimit', kw_args)
+        self.assertEqual(async_utils.QEMU_IMG_PROC_LIMITS,
+                         kw_args.get('prlimit'))
+
     def test_import_flow(self):
         self.config(engine_mode='serial',
                     group='taskflow_executor')
@@ -127,6 +136,8 @@ class TestImportTask(test_utils.BaseTestCase):
                                                    self.image.image_id),
                                  self.image.locations[0]['url'])
 
+                self._assert_qemu_process_limits(tmock)
+
     def test_import_flow_missing_work_dir(self):
         self.config(engine_mode='serial', group='taskflow_executor')
         self.config(work_dir=None, group='task')
@@ -235,6 +246,7 @@ class TestImportTask(test_utils.BaseTestCase):
                     self.assertTrue(rmock.called)
                     self.assertIsInstance(rmock.call_args[1]['result'],
                                           failure.Failure)
+                    self._assert_qemu_process_limits(tmock)
 
                     image_path = os.path.join(self.test_dir,
                                               self.image.image_id)
@@ -283,6 +295,8 @@ class TestImportTask(test_utils.BaseTestCase):
                                       executor.begin_processing,
                                       self.task.task_id)
 
+                    self._assert_qemu_process_limits(tmock)
+
                     image_path = os.path.join(self.test_dir,
                                               self.image.image_id)
                     tmp_image_path = os.path.join(self.work_dir,
@@ -393,6 +407,7 @@ class TestImportTask(test_utils.BaseTestCase):
                 image_path = os.path.join(self.work_dir, image_id)
                 tmp_image_path = os.path.join(self.work_dir, image_path)
                 self.assertTrue(os.path.exists(tmp_image_path))
+                self._assert_qemu_process_limits(tmock)
 
     def test_delete_from_fs(self):
         delete_fs = import_flow._DeleteFromFS(self.task.task_id,

glance/tests/unit/async/flows/test_introspect.py

@@ -21,6 +21,7 @@ from oslo_concurrency import processutils
 from oslo_config import cfg
 
 from glance.async.flows import introspect
+from glance.async import utils as async_utils
 from glance import domain
 import glance.tests.utils as test_utils
 
@@ -89,6 +90,13 @@ class TestImportTask(test_utils.BaseTestCase):
             image_create.execute(image, '/test/path.qcow2')
             self.assertEqual(10737418240, image.virtual_size)
 
+            # NOTE(hemanthm): Assert that process limits are being applied on
+            # "qemu-img info" calls. See bug #1449062 for more details.
+            kw_args = exc_mock.call_args[1]
+            self.assertIn('prlimit', kw_args)
+            self.assertEqual(async_utils.QEMU_IMG_PROC_LIMITS,
+                             kw_args.get('prlimit'))
+
     def test_introspect_no_image(self):
         image_create = introspect._Introspect(self.task.task_id,
                                               self.task_type,

releasenotes/notes/add-processlimits-to-qemu-img-c215f5d90f741d8a.yaml

@@ -0,0 +1,12 @@
+---
+security:
+  - All ``qemu-img info`` calls are now run under resource
+    limitations that limit the CPU time and address space
+    usage of the process running the command to 2 seconds
+    and 1 GB respectively. This addresses the bug
+    https://bugs.launchpad.net/glance/+bug/1449062
+
+    Current usage of "qemu-img" is limited to Glance tasks,
+    which by default (since the Liberty release) are only
+    available to admin users. We continue to recommend that
+    tasks only be exposed to trusted users