Don't use shred for volume clearing

Volume clearing is intended to provide safety against
data leaking between different volumes/tenants when
backing storage is reused.  dd is sufficient to
accomplish this, and since 'shred' does not add anything
meaningful and has not seen much real-world use,
we should remove it for simplicity.

This change makes 'volume_clear=shred' call dd and
warns that this option will be removed.

Change-Id: I190dc22c5edb6efc56b98c5eac870a35c03fcd3f

cinder/tests/unit/test_volume_utils.py

@@ -437,24 +437,33 @@ class ClearVolumeTestCase(test.TestCase):
     @mock.patch('cinder.utils.execute')
     @mock.patch('cinder.volume.utils.CONF')
     def test_clear_volume_shred(self, mock_conf, mock_exec):
+        # 'shred' now uses 'dd'.  Remove this test when
+        # support for 'volume_clear=shred' is removed.
         mock_conf.volume_clear = 'shred'
         mock_conf.volume_clear_size = 1
         mock_conf.volume_clear_ionice = None
+        mock_conf.volume_dd_blocksize = '1M'
         output = volume_utils.clear_volume(1024, 'volume_path')
         self.assertIsNone(output)
-        mock_exec.assert_called_once_with(
-            'shred', '-n3', '-s1MiB', "volume_path", run_as_root=True)
+        mock_exec.assert_called_with(
+            'dd', 'if=/dev/zero', 'of=volume_path', 'count=1', 'bs=1M',
+            'oflag=direct', run_as_root=True)
 
     @mock.patch('cinder.utils.execute')
     @mock.patch('cinder.volume.utils.CONF')
     def test_clear_volume_shred_not_clear_size(self, mock_conf, mock_exec):
+        # 'shred' now uses 'dd'.  Remove this test when
+        # support for 'volume_clear=shred' is removed.
         mock_conf.volume_clear = 'shred'
         mock_conf.volume_clear_size = None
         mock_conf.volume_clear_ionice = None
+        mock_conf.volume_dd_blocksize = '1M'
+        mock_conf.volume_clear_size = 1
         output = volume_utils.clear_volume(1024, 'volume_path')
         self.assertIsNone(output)
-        mock_exec.assert_called_once_with(
-            'shred', '-n3', "volume_path", run_as_root=True)
+        mock_exec.assert_called_with(
+            'dd', 'if=/dev/zero', 'of=volume_path', 'count=1', 'bs=1M',
+            'oflag=direct', run_as_root=True)
 
     @mock.patch('cinder.volume.utils.CONF')
     def test_clear_volume_invalid_opt(self, mock_conf):

cinder/volume/utils.py

@@ -488,6 +488,11 @@ def clear_volume(volume_size, volume_path, volume_clear=None,
 
     LOG.info(_LI("Performing secure delete on volume: %s"), volume_path)
 
+    if volume_clear == 'shred':
+        LOG.warning(_LW("volume_clear=shred has been deprecated and will "
+                        "be removed in the next release. Clearing with dd."))
+        volume_clear = 'zero'
+
     # We pass sparse=False explicitly here so that zero blocks are not
     # skipped in order to clear the volume.
     if volume_clear == 'zero':
@@ -496,26 +501,11 @@ def clear_volume(volume_size, volume_path, volume_clear=None,
                            sync=True, execute=utils.execute,
                            ionice=volume_clear_ionice,
                            throttle=throttle, sparse=False)
-    elif volume_clear == 'shred':
-        clear_cmd = ['shred', '-n3']
-        if volume_clear_size:
-            clear_cmd.append('-s%dMiB' % volume_clear_size)
     else:
         raise exception.InvalidConfigurationValue(
             option='volume_clear',
             value=volume_clear)
 
-    clear_cmd.append(volume_path)
-    start_time = timeutils.utcnow()
-    utils.execute(*clear_cmd, run_as_root=True)
-    duration = timeutils.delta_seconds(start_time, timeutils.utcnow())
-
-    # NOTE(jdg): use a default of 1, mostly for unit test, but in
-    # some incredible event this is 0 (cirros image?) don't barf
-    if duration < 1:
-        duration = 1
-    LOG.info(_LI('Elapsed time for clear volume: %.2f sec'), duration)
-
 
 def supports_thin_provisioning():
     return brick_lvm.LVM.supports_thin_provisioning(

etc/cinder/rootwrap.d/volume.filters

@@ -65,10 +65,6 @@ lvconvert: CommandFilter, lvconvert, root
 # cinder/volume/driver.py: 'iscsiadm', '-m', 'node', '-T', ...
 iscsiadm: CommandFilter, iscsiadm, root
 
-# cinder/volume/drivers/lvm.py: 'shred', '-n3'
-# cinder/volume/drivers/lvm.py: 'shred', '-n0', '-z', '-s%dMiB'
-shred: CommandFilter, shred, root
-
 # cinder/volume/utils.py: utils.temporary_chown(path, 0)
 chown: CommandFilter, chown, root