Make yaml file writes safer (#59384)

homeassistant/components/config/__init__.py

@@ -11,6 +11,7 @@ from homeassistant.const import CONF_ID, EVENT_COMPONENT_LOADED
 from homeassistant.core import callback
 from homeassistant.exceptions import HomeAssistantError
 from homeassistant.setup import ATTR_COMPONENT
+from homeassistant.util.file import write_utf8_file
 from homeassistant.util.yaml import dump, load_yaml
 
 DOMAIN = "config"
@@ -252,6 +253,5 @@ def _write(path, data):
     """Write YAML helper."""
     # Do it before opening file. If dump causes error it will now not
     # truncate the file.
-    data = dump(data)
-    with open(path, "w", encoding="utf-8") as outfile:
-        outfile.write(data)
+    contents = dump(data)
+    write_utf8_file(path, contents)

homeassistant/util/file.py

@@ -0,0 +1,54 @@
+"""File utility functions."""
+from __future__ import annotations
+
+import logging
+import os
+import tempfile
+
+from homeassistant.exceptions import HomeAssistantError
+
+_LOGGER = logging.getLogger(__name__)
+
+
+class WriteError(HomeAssistantError):
+    """Error writing the data."""
+
+
+def write_utf8_file(
+    filename: str,
+    utf8_data: str,
+    private: bool = False,
+) -> None:
+    """Write a file and rename it into place.
+
+    Writes all or nothing.
+    """
+
+    tmp_filename = ""
+    tmp_path = os.path.split(filename)[0]
+    try:
+        # Modern versions of Python tempfile create this file with mode 0o600
+        with tempfile.NamedTemporaryFile(
+            mode="w", encoding="utf-8", dir=tmp_path, delete=False
+        ) as fdesc:
+            fdesc.write(utf8_data)
+            tmp_filename = fdesc.name
+        if not private:
+            os.chmod(tmp_filename, 0o644)
+        os.replace(tmp_filename, filename)
+    except OSError as error:
+        _LOGGER.exception("Saving file failed: %s", filename)
+        raise WriteError(error) from error
+    finally:
+        if os.path.exists(tmp_filename):
+            try:
+                os.remove(tmp_filename)
+            except OSError as err:
+                # If we are cleaning up then something else went wrong, so
+                # we should suppress likely follow-on errors in the cleanup
+                _LOGGER.error(
+                    "File replacement cleanup failed for %s while saving %s: %s",
+                    tmp_filename,
+                    filename,
+                    err,
+                )

homeassistant/util/json.py

@@ -5,13 +5,13 @@ from collections import deque
 from collections.abc import Callable
 import json
 import logging
-import os
-import tempfile
 from typing import Any
 
 from homeassistant.core import Event, State
 from homeassistant.exceptions import HomeAssistantError
 
+from .file import write_utf8_file
+
 _LOGGER = logging.getLogger(__name__)
 
 
@@ -61,29 +61,7 @@ def save_json(
         _LOGGER.error(msg)
         raise SerializationError(msg) from error
 
-    tmp_filename = ""
-    tmp_path = os.path.split(filename)[0]
-    try:
-        # Modern versions of Python tempfile create this file with mode 0o600
-        with tempfile.NamedTemporaryFile(
-            mode="w", encoding="utf-8", dir=tmp_path, delete=False
-        ) as fdesc:
-            fdesc.write(json_data)
-            tmp_filename = fdesc.name
-        if not private:
-            os.chmod(tmp_filename, 0o644)
-        os.replace(tmp_filename, filename)
-    except OSError as error:
-        _LOGGER.exception("Saving JSON file failed: %s", filename)
-        raise WriteError(error) from error
-    finally:
-        if os.path.exists(tmp_filename):
-            try:
-                os.remove(tmp_filename)
-            except OSError as err:
-                # If we are cleaning up then something else went wrong, so
-                # we should suppress likely follow-on errors in the cleanup
-                _LOGGER.error("JSON replacement cleanup failed: %s", err)
+    write_utf8_file(filename, json_data, private)
 
 
 def format_unserializable_data(data: dict[str, Any]) -> str:

tests/components/config/test_group.py

@@ -1,10 +1,14 @@
 """Test Group config panel."""
 from http import HTTPStatus
 import json
+from pathlib import Path
 from unittest.mock import AsyncMock, patch
 
 from homeassistant.bootstrap import async_setup_component
 from homeassistant.components import config
+from homeassistant.components.config import group
+from homeassistant.util.file import write_utf8_file
+from homeassistant.util.yaml import dump, load_yaml
 
 VIEW_NAME = "api:config:group:config"
 
@@ -113,3 +117,49 @@ async def test_update_device_config_invalid_json(hass, hass_client):
     resp = await client.post("/api/config/group/config/hello_beer", data="not json")
 
     assert resp.status == HTTPStatus.BAD_REQUEST
+
+
+async def test_update_config_write_to_temp_file(hass, hass_client, tmpdir):
+    """Test config with a temp file."""
+    test_dir = await hass.async_add_executor_job(tmpdir.mkdir, "files")
+    group_yaml = Path(test_dir / "group.yaml")
+
+    with patch.object(group, "GROUP_CONFIG_PATH", group_yaml), patch.object(
+        config, "SECTIONS", ["group"]
+    ):
+        await async_setup_component(hass, "config", {})
+
+    client = await hass_client()
+
+    orig_data = {
+        "hello.beer": {"ignored": True},
+        "other.entity": {"polling_intensity": 2},
+    }
+    contents = dump(orig_data)
+    await hass.async_add_executor_job(write_utf8_file, group_yaml, contents)
+
+    mock_call = AsyncMock()
+
+    with patch.object(hass.services, "async_call", mock_call):
+        resp = await client.post(
+            "/api/config/group/config/hello_beer",
+            data=json.dumps(
+                {"name": "Beer", "entities": ["light.top", "light.bottom"]}
+            ),
+        )
+        await hass.async_block_till_done()
+
+    assert resp.status == HTTPStatus.OK
+    result = await resp.json()
+    assert result == {"result": "ok"}
+
+    new_data = await hass.async_add_executor_job(load_yaml, group_yaml)
+
+    assert new_data == {
+        **orig_data,
+        "hello_beer": {
+            "name": "Beer",
+            "entities": ["light.top", "light.bottom"],
+        },
+    }
+    mock_call.assert_called_once_with("group", "reload")

tests/util/test_file.py

@@ -0,0 +1,65 @@
+"""Test Home Assistant file utility functions."""
+import os
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+
+from homeassistant.util.file import WriteError, write_utf8_file
+
+
+def test_write_utf8_file_private(tmpdir):
+    """Test files can be written as 0o600 or 0o644."""
+    test_dir = tmpdir.mkdir("files")
+    test_file = Path(test_dir / "test.json")
+
+    write_utf8_file(test_file, '{"some":"data"}', False)
+    with open(test_file) as fh:
+        assert fh.read() == '{"some":"data"}'
+    assert os.stat(test_file).st_mode & 0o777 == 0o644
+
+    write_utf8_file(test_file, '{"some":"data"}', True)
+    with open(test_file) as fh:
+        assert fh.read() == '{"some":"data"}'
+    assert os.stat(test_file).st_mode & 0o777 == 0o600
+
+
+def test_write_utf8_file_fails_at_creation(tmpdir):
+    """Test that failed creation of the temp file does not create an empty file."""
+    test_dir = tmpdir.mkdir("files")
+    test_file = Path(test_dir / "test.json")
+
+    with pytest.raises(WriteError), patch(
+        "homeassistant.util.file.tempfile.NamedTemporaryFile", side_effect=OSError
+    ):
+        write_utf8_file(test_file, '{"some":"data"}', False)
+
+    assert not os.path.exists(test_file)
+
+
+def test_write_utf8_file_fails_at_rename(tmpdir, caplog):
+    """Test that if rename fails not not remove, we do not log the failed cleanup."""
+    test_dir = tmpdir.mkdir("files")
+    test_file = Path(test_dir / "test.json")
+
+    with pytest.raises(WriteError), patch(
+        "homeassistant.util.file.os.replace", side_effect=OSError
+    ):
+        write_utf8_file(test_file, '{"some":"data"}', False)
+
+    assert not os.path.exists(test_file)
+
+    assert "File replacement cleanup failed" not in caplog.text
+
+
+def test_write_utf8_file_fails_at_rename_and_remove(tmpdir, caplog):
+    """Test that if rename and remove both fail, we log the failed cleanup."""
+    test_dir = tmpdir.mkdir("files")
+    test_file = Path(test_dir / "test.json")
+
+    with pytest.raises(WriteError), patch(
+        "homeassistant.util.file.os.remove", side_effect=OSError
+    ), patch("homeassistant.util.file.os.replace", side_effect=OSError):
+        write_utf8_file(test_file, '{"some":"data"}', False)
+
+    assert "File replacement cleanup failed" in caplog.text