Add clean step 'erase_pstore'

Add an automatic clean step to clean the Linux kernel's pstore.
The step is disabled by default.

Story: #2008317
Task: #41214

Change-Id: Ie1a42dfff4c7e1c7abeaf39feca956bb9e2ea497

doc/source/admin/hardware_managers.rst

@@ -35,6 +35,9 @@ Clean steps
 ``deploy.erase_devices_metadata``
     Erases partition tables from all recognized disk devices. Can be used as
     an alternative to the much longer ``erase_devices`` step.
+``deploy.erase_pstore``
+    Erases entries from pstore, the kernel's oops/panic logger. Disabled by
+    default. Can be enabled via priority overrides.
 ``raid.create_configuration``
     Create a RAID configuration. This step belongs to the ``raid`` interface
     and must be used through the :ironic-doc:`ironic RAID feature

ironic_python_agent/hardware.py

@@ -22,6 +22,7 @@ from multiprocessing.pool import ThreadPool
 import os
 import re
 import shlex
+import shutil
 import time
 
 from ironic_lib import disk_utils
@@ -1314,6 +1315,37 @@ class GenericHardwareManager(HardwareManager):
                                     for k, v in erase_errors.items()]))
             raise errors.BlockDeviceEraseError(excpt_msg)
 
+    def _find_pstore_mount_point(self):
+        """Find the pstore mount point by scanning /proc/mounts.
+
+        :returns: The pstore mount if existing, none otherwise.
+        """
+        with open("/proc/mounts", "r") as mounts:
+            for line in mounts:
+                # /proc/mounts format is: "device mountpoint fstype ..."
+                m = re.match(r'^pstore (\S+) pstore', line)
+                if m:
+                    return m.group(1)
+
+    def erase_pstore(self, node, ports):
+        """Attempt to erase the kernel pstore.
+
+        :param node: Ironic node object
+        :param ports: list of Ironic port objects
+        """
+        pstore_path = self._find_pstore_mount_point()
+        if not pstore_path:
+            LOG.debug("No pstore found")
+            return
+
+        LOG.info("Cleaning up pstore in %s", pstore_path)
+        for file in os.listdir(pstore_path):
+            filepath = os.path.join(pstore_path, file)
+            try:
+                shutil.rmtree(filepath)
+            except OSError:
+                os.remove(filepath)
+
     def _shred_block_device(self, node, block_device):
         """Erase a block device using shred.
 
@@ -1680,6 +1712,13 @@ class GenericHardwareManager(HardwareManager):
                 'reboot_requested': False,
                 'abortable': True
             },
+            {
+                'step': 'erase_pstore',
+                'priority': 0,
+                'interface': 'deploy',
+                'reboot_requested': False,
+                'abortable': True
+            },
             {
                 'step': 'delete_configuration',
                 'priority': 0,

ironic_python_agent/tests/unit/test_hardware.py

@@ -14,6 +14,7 @@
 
 import binascii
 import os
+import shutil
 import time
 from unittest import mock
 
@@ -859,6 +860,24 @@ MDADM_EXAMINE_OUTPUT_NON_MEMBER = ("""/dev/sdz1:
 """)
 
 
+PROC_MOUNTS_OUTPUT = ("""
+debugfs /sys/kernel/debug debugfs rw,relatime 0 0
+/dev/sda2 / ext4 rw,relatime,errors=remount-ro 0 0
+tmpfs /run/user/1000 tmpfs rw,nosuid,nodev,relatime  0 0
+pstore /sys/fs/pstore pstore rw,nosuid,nodev,noexec,relatime 0 0
+/dev/loop19 /snap/core/10126 squashfs ro,nodev,relatime 0 0
+""")
+
+
+PROC_MOUNTS_OUTPUT_NO_PSTORE = ("""
+debugfs /sys/kernel/debug debugfs rw,relatime 0 0
+/dev/sda2 / ext4 rw,relatime,errors=remount-ro 0 0
+tmpfs /run/user/1000 tmpfs rw,nosuid,nodev,relatime  0 0
+pstore /sys/fs/pstore qstore rw,nosuid,nodev,noexec,relatime 0 0
+/dev/loop19 /snap/core/10126 squashfs ro,nodev,relatime 0 0
+""")
+
+
 class FakeHardwareManager(hardware.GenericHardwareManager):
     def __init__(self, hardware_support):
         self._hardware_support = hardware_support
@@ -921,6 +940,13 @@ class TestGenericHardwareManager(base.IronicAgentTest):
                 'reboot_requested': False,
                 'abortable': True
             },
+            {
+                'step': 'erase_pstore',
+                'priority': 0,
+                'interface': 'deploy',
+                'reboot_requested': False,
+                'abortable': True
+            },
             {
                 'step': 'delete_configuration',
                 'priority': 0,
@@ -2631,6 +2657,44 @@ class TestGenericHardwareManager(base.IronicAgentTest):
         test_security_erase_option(
             self, False, '--security-erase')
 
+    def test__find_pstore_mount_point(self):
+        with mock.patch('builtins.open',
+                        mock.mock_open(),
+                        create=True) as mocked_open:
+            mocked_open.return_value.__iter__ = \
+                lambda self: iter(PROC_MOUNTS_OUTPUT.splitlines())
+
+            self.assertEqual(self.hardware._find_pstore_mount_point(),
+                             "/sys/fs/pstore")
+            mocked_open.assert_called_once_with('/proc/mounts', 'r')
+
+    def test__find_pstore_mount_point_no_pstore(self):
+        with mock.patch('builtins.open',
+                        mock.mock_open(),
+                        create=True) as mocked_open:
+            mocked_open.return_value.__iter__.return_value = \
+                PROC_MOUNTS_OUTPUT_NO_PSTORE.splitlines()
+            self.assertIsNone(self.hardware._find_pstore_mount_point())
+            mocked_open.assert_called_once_with('/proc/mounts', 'r')
+
+    @mock.patch('os.listdir', autospec=True)
+    @mock.patch.object(shutil, 'rmtree', autospec=True)
+    @mock.patch.object(hardware.GenericHardwareManager,
+                       '_find_pstore_mount_point', autospec=True)
+    def test_erase_pstore(self, mocked_find_pstore, mocked_rmtree,
+                          mocked_listdir):
+        mocked_find_pstore.return_value = '/sys/fs/pstore'
+        pstore_entries = ['dmesg-erst-663482778',
+                          'dmesg-erst-663482779']
+        mocked_listdir.return_value = pstore_entries
+        self.hardware.erase_pstore(self.node, [])
+        mocked_listdir.assert_called_once()
+        self.assertEqual(mocked_rmtree.call_count,
+                         len(pstore_entries))
+        mocked_rmtree.assert_has_calls([
+            mock.call('/sys/fs/pstore/' + arg) for arg in pstore_entries
+        ])
+
     @mock.patch.object(utils, 'execute', autospec=True)
     @mock.patch.object(hardware.GenericHardwareManager,
                        '_is_virtual_media_device', autospec=True)

releasenotes/notes/add_erase_pstore-b109c58ed8f5d351.yaml

@@ -0,0 +1,11 @@
+---
+features:
+  - |
+    Adds a clean step to erase the Linux kernel's pstore. The step is disabled
+    by default.
+security:
+  - |
+    If enabled, the new clean step 'erase_pstore' removes all pstore entries
+    (the oops/panic logs from a failing kernel) upon cleaning. This is to
+    reduce the risk that potentially sensitive data is preserved across
+    instantiations (and therefore different users) of a bare metal node.