fix(assessment): harden capability evidence trust

tests/test_capability_fit_atomic_io.py

@@ -0,0 +1,190 @@
+from __future__ import annotations
+
+import json
+import os
+from pathlib import Path
+import stat
+import sys
+import tempfile
+import unittest
+from unittest import mock
+
+
+META_ROOT = Path(__file__).resolve().parents[1]
+ASSESSMENT_TOOLS_ROOT = META_ROOT / "tools" / "assessments"
+RELEASE_TOOLS_ROOT = META_ROOT / "tools" / "release"
+for tools_root in (ASSESSMENT_TOOLS_ROOT, RELEASE_TOOLS_ROOT):
+    if str(tools_root) not in sys.path:
+        sys.path.insert(0, str(tools_root))
+
+from govoplan_assessment.atomic_io import (  # noqa: E402
+    AtomicJsonWriteError,
+    atomic_write_json,
+)
+
+
+class CapabilityFitAtomicIOTests(unittest.TestCase):
+    def test_writes_private_json_with_expected_content(self) -> None:
+        with tempfile.TemporaryDirectory() as temporary_directory:
+            target = Path(temporary_directory) / "evidence.json"
+            payload = {"z": [1, 2], "message": "Grüße"}
+            created_in: list[Path] = []
+            original_mkstemp = tempfile.mkstemp
+
+            def observed_mkstemp(*args, **kwargs):
+                created_in.append(Path(kwargs["dir"]))
+                return original_mkstemp(*args, **kwargs)
+
+            with (
+                mock.patch(
+                    "govoplan_assessment.atomic_io.tempfile.mkstemp",
+                    side_effect=observed_mkstemp,
+                ),
+                mock.patch(
+                    "govoplan_assessment.atomic_io.os.fsync",
+                    wraps=os.fsync,
+                ) as fsync,
+            ):
+                atomic_write_json(target, payload, max_bytes=1024)
+
+            self.assertEqual(payload, json.loads(target.read_text(encoding="utf-8")))
+            self.assertTrue(target.read_bytes().endswith(b"\n"))
+            self.assertEqual(0o600, stat.S_IMODE(target.stat().st_mode))
+            self.assertEqual([target.parent], created_in)
+            self.assertEqual(2, fsync.call_count)
+
+    def test_replaces_existing_regular_file_and_secures_mode(self) -> None:
+        with tempfile.TemporaryDirectory() as temporary_directory:
+            target = Path(temporary_directory) / "report.json"
+            target.write_text('{"old": true}\n', encoding="utf-8")
+            target.chmod(0o644)
+            old_handle = target.open("rb")
+            self.addCleanup(old_handle.close)
+
+            atomic_write_json(target, {"new": True}, max_bytes=1024)
+
+            self.assertEqual(b'{"old": true}\n', old_handle.read())
+            self.assertEqual({"new": True}, json.loads(target.read_text("utf-8")))
+            self.assertEqual(0o600, stat.S_IMODE(target.stat().st_mode))
+
+    def test_size_bound_leaves_existing_target_unchanged(self) -> None:
+        with tempfile.TemporaryDirectory() as temporary_directory:
+            directory = Path(temporary_directory)
+            target = directory / "evidence.json"
+            original = b'{"original": true}\n'
+            target.write_bytes(original)
+
+            with self.assertRaisesRegex(AtomicJsonWriteError, "size limit"):
+                atomic_write_json(target, {"large": "x" * 100}, max_bytes=32)
+
+            self.assertEqual(original, target.read_bytes())
+            self.assertEqual([], list(directory.glob(".govoplan-json-*.tmp")))
+
+    @unittest.skipUnless(hasattr(os, "symlink"), "symbolic links are unavailable")
+    def test_rejects_symlink_without_modifying_link_or_referent(self) -> None:
+        with tempfile.TemporaryDirectory() as temporary_directory:
+            directory = Path(temporary_directory)
+            referent = directory / "outside.json"
+            referent.write_bytes(b'{"keep": true}\n')
+            target = directory / "evidence.json"
+            target.symlink_to(referent.name)
+
+            with self.assertRaisesRegex(AtomicJsonWriteError, "symbolic link"):
+                atomic_write_json(target, {"replace": True}, max_bytes=1024)
+
+            self.assertTrue(target.is_symlink())
+            self.assertEqual(b'{"keep": true}\n', referent.read_bytes())
+            self.assertEqual([], list(directory.glob(".govoplan-json-*.tmp")))
+
+    @unittest.skipUnless(hasattr(os, "symlink"), "symbolic links are unavailable")
+    def test_rejects_symlinked_parent_component(self) -> None:
+        with tempfile.TemporaryDirectory() as temporary_directory:
+            directory = Path(temporary_directory)
+            real_parent = directory / "real-parent"
+            real_parent.mkdir()
+            linked_parent = directory / "linked-parent"
+            linked_parent.symlink_to(real_parent, target_is_directory=True)
+            target = linked_parent / "new" / "evidence.json"
+
+            with self.assertRaisesRegex(AtomicJsonWriteError, "parent path"):
+                atomic_write_json(target, {"unsafe": True}, max_bytes=1024)
+
+            self.assertFalse((real_parent / "new").exists())
+
+    def test_requires_existing_parent_without_creating_directories(self) -> None:
+        with tempfile.TemporaryDirectory() as temporary_directory:
+            directory = Path(temporary_directory)
+            missing_parent = directory / "missing" / "nested"
+            target = missing_parent / "evidence.json"
+
+            with self.assertRaisesRegex(AtomicJsonWriteError, "already exist"):
+                atomic_write_json(target, {"safe": True}, max_bytes=1024)
+
+            self.assertFalse(missing_parent.exists())
+
+    def test_rejects_post_replace_mode_or_identity_change(self) -> None:
+        with tempfile.TemporaryDirectory() as temporary_directory:
+            directory = Path(temporary_directory)
+            target = directory / "evidence.json"
+            original_replace = os.replace
+
+            def insecure_replace(source, destination):
+                original_replace(source, destination)
+                Path(destination).chmod(0o644)
+
+            with mock.patch(
+                "govoplan_assessment.atomic_io.os.replace",
+                side_effect=insecure_replace,
+            ):
+                with self.assertRaisesRegex(
+                    AtomicJsonWriteError,
+                    "permissions changed and were restored",
+                ):
+                    atomic_write_json(target, {"safe": True}, max_bytes=1024)
+
+            self.assertEqual(0o600, stat.S_IMODE(target.stat().st_mode))
+            self.assertEqual({"safe": True}, json.loads(target.read_text("utf-8")))
+
+    def test_does_not_unlink_unknown_post_replace_inode(self) -> None:
+        with tempfile.TemporaryDirectory() as temporary_directory:
+            directory = Path(temporary_directory)
+            target = directory / "evidence.json"
+            original_replace = os.replace
+
+            def replaced_again(source, destination):
+                original_replace(source, destination)
+                Path(destination).unlink()
+                Path(destination).write_bytes(b"unknown replacement\n")
+
+            with mock.patch(
+                "govoplan_assessment.atomic_io.os.replace",
+                side_effect=replaced_again,
+            ):
+                with self.assertRaisesRegex(
+                    AtomicJsonWriteError,
+                    "did not preserve",
+                ):
+                    atomic_write_json(target, {"secret": True}, max_bytes=1024)
+
+            self.assertEqual(b"unknown replacement\n", target.read_bytes())
+
+    def test_replace_failure_removes_private_temporary_file(self) -> None:
+        with tempfile.TemporaryDirectory() as temporary_directory:
+            directory = Path(temporary_directory)
+            target = directory / "evidence.json"
+
+            with mock.patch(
+                "govoplan_assessment.atomic_io.os.replace",
+                side_effect=OSError("simulated replacement failure"),
+            ):
+                with self.assertRaisesRegex(
+                    AtomicJsonWriteError, "could not be written atomically"
+                ):
+                    atomic_write_json(target, {"safe": True}, max_bytes=1024)
+
+            self.assertFalse(target.exists())
+            self.assertEqual([], list(directory.glob(".govoplan-json-*.tmp")))
+
+
+if __name__ == "__main__":
+    unittest.main()