fix(assessment): harden capability evidence trust

tools/assessments/govoplan_assessment/atomic_io.py

@@ -0,0 +1,230 @@
+"""Bounded, private, atomic JSON output for assessment evidence."""
+
+from __future__ import annotations
+
+import json
+import os
+from pathlib import Path
+import stat
+import tempfile
+from typing import Any
+
+
+class AtomicJsonWriteError(RuntimeError):
+    """Raised when JSON output cannot be written with the required guarantees."""
+
+
+def atomic_write_json(
+    path: str | os.PathLike[str],
+    payload: Any,
+    *,
+    max_bytes: int,
+) -> None:
+    """Write bounded JSON through a private same-directory temporary file.
+
+    A successful return means the file contents and the containing directory
+    entry have both been flushed. If flushing the directory fails after the
+    atomic replacement, the replacement may be visible but its crash
+    durability is unknown, so the function reports failure. Every parent must
+    already exist as a real directory; symbolic-link components are rejected.
+    """
+
+    if isinstance(max_bytes, bool) or not isinstance(max_bytes, int) or max_bytes <= 0:
+        raise ValueError("max_bytes must be a positive integer")
+
+    encoded = _encode_bounded_json(payload, max_bytes=max_bytes)
+    target = Path(os.path.abspath(os.fspath(path)))
+    parent = target.parent
+    descriptor = -1
+    verification_descriptor = -1
+    temporary_path: Path | None = None
+    temporary_identity: tuple[int, int] | None = None
+
+    try:
+        _assert_real_parent(parent)
+        _assert_replaceable_target(target)
+        try:
+            descriptor, temporary_name = tempfile.mkstemp(
+                dir=parent,
+                prefix=".govoplan-json-",
+                suffix=".tmp",
+            )
+            temporary_path = Path(temporary_name)
+            os.fchmod(descriptor, 0o600)
+            metadata = os.fstat(descriptor)
+            if (
+                not stat.S_ISREG(metadata.st_mode)
+                or stat.S_IMODE(metadata.st_mode) != 0o600
+            ):
+                raise AtomicJsonWriteError(
+                    "Atomic JSON temporary file could not be secured."
+                )
+            temporary_identity = (metadata.st_dev, metadata.st_ino)
+            verification_descriptor = os.dup(descriptor)
+
+            handle = os.fdopen(descriptor, "wb")
+            descriptor = -1
+            with handle:
+                handle.write(encoded)
+                handle.flush()
+                os.fsync(handle.fileno())
+
+            # Recheck after creating and flushing the temporary file so an
+            # unsafe target discovered before replacement is never followed.
+            _assert_real_parent(parent)
+            _assert_replaceable_target(target)
+            os.replace(temporary_path, target)
+            temporary_path = None
+            _assert_installed_target(
+                target,
+                expected_identity=temporary_identity,
+                recovery_descriptor=verification_descriptor,
+            )
+            _fsync_directory(parent)
+        finally:
+            try:
+                if descriptor >= 0:
+                    os.close(descriptor)
+            finally:
+                try:
+                    if verification_descriptor >= 0:
+                        os.close(verification_descriptor)
+                finally:
+                    if temporary_path is not None:
+                        try:
+                            temporary_path.unlink()
+                        except FileNotFoundError:
+                            pass
+    except AtomicJsonWriteError:
+        raise
+    except OSError as exc:
+        raise AtomicJsonWriteError(
+            "JSON output could not be written atomically."
+        ) from exc
+
+
+def _encode_bounded_json(payload: Any, *, max_bytes: int) -> bytes:
+    encoder = json.JSONEncoder(
+        allow_nan=False,
+        ensure_ascii=False,
+        indent=2,
+        sort_keys=True,
+    )
+    chunks: list[bytes] = []
+    encoded_size = 1  # The document always ends with one newline.
+    for chunk in encoder.iterencode(payload):
+        encoded_chunk = chunk.encode("utf-8")
+        encoded_size += len(encoded_chunk)
+        if encoded_size > max_bytes:
+            raise AtomicJsonWriteError("JSON output exceeds its size limit.")
+        chunks.append(encoded_chunk)
+    return b"".join(chunks) + b"\n"
+
+
+def _assert_replaceable_target(path: Path) -> None:
+    try:
+        metadata = path.lstat()
+    except FileNotFoundError:
+        return
+    except OSError as exc:
+        raise AtomicJsonWriteError(
+            "JSON output target could not be inspected safely."
+        ) from exc
+    if stat.S_ISLNK(metadata.st_mode):
+        raise AtomicJsonWriteError("JSON output target must not be a symbolic link.")
+    if not stat.S_ISREG(metadata.st_mode):
+        raise AtomicJsonWriteError("JSON output target must be a regular file.")
+
+
+def _assert_real_parent(path: Path) -> None:
+    current = Path(path.anchor)
+    for part in path.parts[1:]:
+        current /= part
+        try:
+            metadata = current.lstat()
+        except FileNotFoundError as exc:
+            raise AtomicJsonWriteError(
+                "JSON output parent directory must already exist."
+            ) from exc
+        except OSError as exc:
+            raise AtomicJsonWriteError(
+                "JSON output parent directory could not be inspected safely."
+            ) from exc
+        if stat.S_ISLNK(metadata.st_mode):
+            raise AtomicJsonWriteError(
+                "JSON output parent path must not contain symbolic links."
+            )
+        if not stat.S_ISDIR(metadata.st_mode):
+            raise AtomicJsonWriteError(
+                "JSON output parent path must contain only directories."
+            )
+
+
+def _assert_installed_target(
+    path: Path,
+    *,
+    expected_identity: tuple[int, int] | None,
+    recovery_descriptor: int,
+) -> None:
+    try:
+        metadata = path.lstat()
+    except OSError as exc:
+        raise AtomicJsonWriteError(
+            "Atomic JSON replacement could not be verified."
+        ) from exc
+    observed_identity = (metadata.st_dev, metadata.st_ino)
+    if (
+        expected_identity is None
+        or observed_identity != expected_identity
+        or not stat.S_ISREG(metadata.st_mode)
+    ):
+        raise AtomicJsonWriteError(
+            "Atomic JSON replacement did not preserve the secured regular file."
+        )
+    if stat.S_IMODE(metadata.st_mode) == 0o600:
+        return
+    try:
+        recovery_metadata = os.fstat(recovery_descriptor)
+        if (
+            not stat.S_ISREG(recovery_metadata.st_mode)
+            or (recovery_metadata.st_dev, recovery_metadata.st_ino) != expected_identity
+        ):
+            raise AtomicJsonWriteError(
+                "Atomic JSON replacement recovery descriptor is invalid."
+            )
+        os.fchmod(recovery_descriptor, 0o600)
+        os.fsync(recovery_descriptor)
+        recovered_metadata = os.fstat(recovery_descriptor)
+        installed_metadata = path.lstat()
+    except OSError as exc:
+        raise AtomicJsonWriteError(
+            "Atomic JSON replacement permissions could not be restored."
+        ) from exc
+    if (
+        stat.S_IMODE(recovered_metadata.st_mode) != 0o600
+        or (installed_metadata.st_dev, installed_metadata.st_ino) != expected_identity
+        or not stat.S_ISREG(installed_metadata.st_mode)
+        or stat.S_IMODE(installed_metadata.st_mode) != 0o600
+    ):
+        raise AtomicJsonWriteError(
+            "Atomic JSON replacement permissions could not be restored."
+        )
+    _fsync_directory(path.parent)
+    raise AtomicJsonWriteError(
+        "Atomic JSON replacement permissions changed and were restored."
+    )
+
+
+def _fsync_directory(path: Path) -> None:
+    flags = os.O_RDONLY
+    if hasattr(os, "O_DIRECTORY"):
+        flags |= os.O_DIRECTORY
+    if hasattr(os, "O_NOFOLLOW"):
+        flags |= os.O_NOFOLLOW
+    descriptor = os.open(path, flags)
+    try:
+        if not stat.S_ISDIR(os.fstat(descriptor).st_mode):
+            raise AtomicJsonWriteError("JSON output parent path must be a directory.")
+        os.fsync(descriptor)
+    finally:
+        os.close(descriptor)

tools/assessments/govoplan_assessment/capability_fit.py

@@ -28,6 +28,7 @@ from govoplan_release.version_alignment import candidate_catalog_version_issues
 from .evidence import (
     BoundaryEvidenceReview,
     InstalledEvidenceReview,
+    public_key_material_from_keyrings,
     review_boundary_evidence,
     review_installed_composition,
 )
@@ -63,6 +64,8 @@ def review_capability_fit(
     boundary_authority_keyring: dict[str, Any] | None = None,
     boundary_authority_keyring_schema: dict[str, Any] | None = None,
     verification_time: datetime | None = None,
+    installed_evidence_mode: str = "imported_unsigned",
+    expected_external_provider_subject: str | None = None,
 ) -> dict[str, Any]:
     """Return a secret-free release-drift report for one fit assessment."""
 
@@ -356,6 +359,10 @@ def review_capability_fit(
             )
         )
 
+    evidence_verification_time = verification_time or datetime.now(tz=UTC)
+    evidence_verification_mode = (
+        "historical_override" if verification_time is not None else "current"
+    )
     installed_review = review_installed_composition(
         assessment=assessment,
         catalog_entries=catalog_entries,
@@ -363,6 +370,9 @@ def review_capability_fit(
         selected_commits=source_selection.selected_commits,
         evidence=installed_evidence,
         schema=installed_evidence_schema,
+        observation_mode=installed_evidence_mode,
+        verification_time=evidence_verification_time,
+        verification_mode=evidence_verification_mode,
     )
     findings.extend(
         Finding(item.severity, item.code, item.message, item.assessment_ids)
@@ -378,7 +388,13 @@ def review_capability_fit(
         evidence_schema=boundary_evidence_schema,
         authority_keyring=boundary_authority_keyring,
         authority_keyring_schema=boundary_authority_keyring_schema,
-        verification_time=verification_time,
+        verification_time=evidence_verification_time,
+        verification_mode=evidence_verification_mode,
+        expected_external_provider_subject=expected_external_provider_subject,
+        forbidden_authority_public_keys=public_key_material_from_keyrings(
+            published_keyring,
+            trusted_keyring,
+        ),
     )
     findings.extend(
         Finding(item.severity, item.code, item.message, item.assessment_ids)
@@ -396,6 +412,7 @@ def review_capability_fit(
             assessment=assessment,
             installed_review=installed_review,
         ),
+        boundary_review.review_targets,
     )
     return build_report(
         assessment=assessment,
@@ -908,7 +925,7 @@ def build_report(
         **boundary_scope,
     }
     return {
-        "report_version": "0.2.0",
+        "report_version": "0.3.0",
         "status": status,
         "assessment_id": assessment.get("assessment_id"),
         "assessment_release": assessment.get("release", {}).get("ref")
@@ -930,9 +947,11 @@ def build_report(
 
 
 def render_review(report: dict[str, Any]) -> str:
-    installed_checked = (
-        report.get("proof_scope", {}).get("installed_artifacts", {}).get("checked")
-        is True
+    proof_scope = report.get("proof_scope", {})
+    installed_scope = proof_scope.get("installed_artifacts", {})
+    installed_checked = installed_scope.get("checked") is True
+    installed_supplied = bool(installed_scope.get("evidence_sha256")) or (
+        "installed_evidence_observation" in proof_scope
     )
     lines = [
         f"Capability fit rerun: {report['status']}",
@@ -941,12 +960,29 @@ def render_review(report: dict[str, Any]) -> str:
         (
             "Scope: schema, signed release metadata, optional local tag provenance, "
             + (
-                "and supplied installed-composition evidence."
+                "and locally observed installed-composition evidence."
                 if installed_checked
-                else "and no installed-composition evidence."
+                else (
+                    "and supplied installed-composition evidence that did not establish local proof."
+                    if installed_supplied
+                    else "and no installed-composition evidence."
+                )
             )
         ),
     ]
+    verification = proof_scope.get("boundary_evidence_verification") or proof_scope.get(
+        "installed_evidence_observation"
+    )
+    if isinstance(verification, dict) and verification.get("evaluated_at"):
+        mode = verification.get("verification_mode")
+        mode_label = (
+            "HISTORICAL override"
+            if mode == "historical_override"
+            else "current-time evaluation"
+        )
+        lines.append(
+            f"Evidence verification: {mode_label} at {verification['evaluated_at']}."
+        )
     findings = report.get("findings") or []
     if findings:
         lines.append("Findings:")