fix(v2): enforce repository protocol safety

backend/src/backup_tool/api/app.py

@@ -26,7 +26,12 @@ from backup_tool.db.models import (
     Session,
     User,
 )
-from backup_tool.repository import RepositoryError, initialize, inspect_repository
+from backup_tool.repository import (
+    RepositoryError,
+    initialize,
+    inspect_repository,
+    remove_repository,
+)
 from backup_tool.security.auth import (
     hash_password,
     hash_token,
@@ -529,10 +534,17 @@ def create_app(settings: Settings) -> FastAPI:
             compression=initialized.compression,
             encryption=initialized.encryption,
         )
-        db.add(repository)
-        await db.flush()
-        await audit(db, request, "create", "repository", repository.id, "success", user.id)
-        await db.commit()
+        try:
+            db.add(repository)
+            await db.flush()
+            await audit(db, request, "create", "repository", repository.id, "success", user.id)
+            await db.commit()
+        except Exception as error:
+            await db.rollback()
+            remove_repository(initialized.root)
+            raise Problem(
+                409, "repository_create_failed", "Repository metadata could not be stored."
+            ) from error
         return {
             "id": repository.id,
             "name": repository.name,
@@ -589,7 +601,7 @@ def create_app(settings: Settings) -> FastAPI:
         if repository is None:
             raise Problem(404, "resource_not_found", "Repository was not found.")
         try:
-            inspected = inspect_repository(Path(repository.root))
+            inspected = inspect_repository(settings, Path(repository.root))
         except RepositoryError as error:
             raise Problem(409, "repository_invalid", str(error)) from error
         return {

backend/src/backup_tool/repository.py

@@ -5,9 +5,11 @@ import json
 import os
 import shutil
 from dataclasses import dataclass
+from datetime import UTC, datetime
 from pathlib import Path
 
 from backup_tool.config import Settings
+from backup_tool.ids import new_uuid7
 
 
 class RepositoryError(ValueError):
@@ -38,7 +40,14 @@ def _contained(root: Path, relative_path: str) -> Path:
 def _canonical_payload(compression: str, encryption: str) -> dict[str, object]:
     if compression != "none" or encryption != "none":
         raise RepositoryError("requested repository policy is unavailable")
-    return {"compression": compression, "encryption": encryption, "format_version": 1}
+    return {
+        "repository_id": str(new_uuid7()),
+        "format_version": 1,
+        "digest_algorithm": "sha256",
+        "compression": compression,
+        "encryption": {"mode": "none", "key_id": None},
+        "created_at": datetime.now(UTC).isoformat(timespec="microseconds").replace("+00:00", "Z"),
+    }
 
 
 def _canonical_json(payload: dict[str, object]) -> str:
@@ -76,8 +85,24 @@ def initialize(
     return InitializedRepository(root=root, compression=compression, encryption=encryption)
 
 
-def inspect_repository(root: Path) -> InitializedRepository:
-    metadata = root / "repository.json"
+def remove_repository(root: Path) -> None:
+    try:
+        shutil.rmtree(root)
+    except FileNotFoundError:
+        return
+
+
+def inspect_repository(settings: Settings, root: Path) -> InitializedRepository:
+    try:
+        resolved_root = root.resolve(strict=True)
+    except OSError as error:
+        raise RepositoryError("repository root is unreadable") from error
+    if root.is_symlink() or not any(
+        resolved_root != allowed.resolve() and allowed.resolve() in resolved_root.parents
+        for allowed in settings.repository_roots
+    ):
+        raise RepositoryError("repository root escapes configured roots")
+    metadata = resolved_root / "repository.json"
     try:
         raw = metadata.read_text(encoding="utf-8")
         payload = json.loads(raw)
@@ -85,12 +110,31 @@ def inspect_repository(root: Path) -> InitializedRepository:
         raise RepositoryError("repository metadata is unreadable") from error
     if not isinstance(payload, dict):
         raise RepositoryError("repository metadata is invalid")
-    try:
-        expected = _canonical_json(
-            _canonical_payload(payload["compression"], payload["encryption"])
-        )
-    except (KeyError, TypeError, RepositoryError) as error:
-        raise RepositoryError("repository metadata is invalid") from error
-    if payload.get("format_version") != 1 or raw != expected:
+    required = {
+        "repository_id",
+        "format_version",
+        "digest_algorithm",
+        "compression",
+        "encryption",
+        "created_at",
+    }
+    if (
+        set(payload) != required
+        or payload.get("format_version") != 1
+        or payload.get("digest_algorithm") != "sha256"
+    ):
         raise RepositoryError("repository metadata is not canonical")
-    return InitializedRepository(root=root, compression="none", encryption="none")
+    encryption = payload.get("encryption")
+    if payload.get("compression") != "none" or encryption != {"mode": "none", "key_id": None}:
+        raise RepositoryError("repository metadata is invalid")
+    try:
+        from uuid import UUID
+
+        UUID(str(payload["repository_id"]))
+        created_at = str(payload["created_at"])
+        if not created_at.endswith("Z"):
+            raise ValueError
+        datetime.fromisoformat(created_at[:-1] + "+00:00")
+    except (ValueError, TypeError) as error:
+        raise RepositoryError("repository metadata is invalid") from error
+    return InitializedRepository(root=resolved_root, compression="none", encryption="none")

tests/integration/test_repository_safety.py

@@ -45,7 +45,7 @@ def test_repository_inspection_rejects_noncanonical_metadata(tmp_path: Path) ->
         '{"encryption":"none","compression":"none","format_version":1}\n'
     )
     with pytest.raises(RepositoryError, match="canonical"):
-        inspect_repository(result.root)
+        inspect_repository(settings, result.root)
 
 
 @pytest.mark.asyncio

tests/security/test_session_security.py

@@ -148,7 +148,8 @@ async def test_logout_revocation_survives_app_restart(tmp_path) -> None:
         transport=ASGITransport(restarted), base_url=settings.public_base_url
     ) as client:
         rejected = await client.get(
-            "/api/v2/auth/session", headers={"Cookie": f"backup_tool_session={copied_cookie}"}
+            "/api/v2/auth/session",
+            headers={"Cookie": f"backup_tool_session={copied_cookie}"},
         )
     assert rejected.status_code == 401
     await restarted.state.engine.dispose()