read_dmi_data: always return None when inside a container.

This fixes stacktrace and warning message that would be printed
to the log if running inside a container and read_dmi_data tried
to access a key that was not present.

In a container, the /sys/class/dmi/id data is not relevant to the
but to the host.  Additionally an unpriviledged container might see
strange behavior:
   # cd /sys/class/dmi/id/
   # id -u
   0
   # ls -l chassis_serial
   -r-------- 1 nobody nogroup 4096 Jun 29 16:49 chassis_serial
   # cat chassis_serial
   cat: /sys/class/dmi/id/chassis_serial: Permission denied

The solution here is to just always return None when running in a
container.

LP: #1701325

1 files changed, 23 insertions, 0 deletions

diff --git a/tests/unittests/test_util.py b/tests/unittests/test_util.py
index a73fd26a..65035be2 100644
--- a/tests/unittests/test_util.py
+++ b/tests/unittests/test_util.py
@@ -365,6 +365,9 @@ class TestReadDMIData(helpers.FilesystemMockingTestCase):
         self.addCleanup(shutil.rmtree, self.new_root)
         self.patchOS(self.new_root)
         self.patchUtils(self.new_root)
+        p = mock.patch("cloudinit.util.is_container", return_value=False)
+        self.addCleanup(p.stop)
+        self._m_is_container = p.start()
 
     def _create_sysfs_parent_directory(self):
         util.ensure_dir(os.path.join('sys', 'class', 'dmi', 'id'))
@@ -453,6 +456,26 @@ class TestReadDMIData(helpers.FilesystemMockingTestCase):
         self._create_sysfs_file(sysfs_key, dmi_value)
         self.assertEqual(expected, util.read_dmi_data(dmi_key))
 
+    def test_container_returns_none(self):
+        """In a container read_dmi_data should always return None."""
+
+        # first verify we get the value if not in container
+        self._m_is_container.return_value = False
+        key, val = ("system-product-name", "my_product")
+        self._create_sysfs_file('product_name', val)
+        self.assertEqual(val, util.read_dmi_data(key))
+
+        # then verify in container returns None
+        self._m_is_container.return_value = True
+        self.assertIsNone(util.read_dmi_data(key))
+
+    def test_container_returns_none_on_unknown(self):
+        """In a container even bogus keys return None."""
+        self._m_is_container.return_value = True
+        self._create_sysfs_file('product_name', "should-be-ignored")
+        self.assertIsNone(util.read_dmi_data("bogus"))
+        self.assertIsNone(util.read_dmi_data("system-product-name"))
+
 
 class TestMultiLog(helpers.FilesystemMockingTestCase):