Fix: Blacklist certain OCR user arguments that paperless itself controls/uses

docs/configuration.md

@@ -1157,6 +1157,9 @@ they use underscores instead of dashes.
         be changed by trusted users. This applies to the `AppConfig` permission as well,
         which allows setting these arguments from the UI.
 
+        Arguments paperless manages itself (`input_file_or_options`, `output_file`
+        and `sidecar`) are rejected by the API and ignored if set here.
+
     Specify arguments as a JSON dictionary. Keep note of lower case
     booleans and double quoted parameter names and strings. Examples:
 

src/documents/tests/test_api_app_config.py

@@ -287,6 +287,28 @@ class TestApiAppConfig(DirectoriesMixin, APITestCase):
         self.assertEqual(config.user_args, user_args)
         self.assertEqual(config.barcode_tag_mapping, barcode_tag_mapping)
 
+    def test_api_update_config_rejects_reserved_user_args(self) -> None:
+        """
+        GIVEN:
+            - API request to update app config with user_args which set an
+              argument the parser manages itself
+        WHEN:
+            - API is called
+        THEN:
+            - Request is rejected with a 400 naming the argument
+            - Config is not updated
+        """
+        response = self.client.patch(
+            f"{self.ENDPOINT}1/",
+            json.dumps({"user_args": json.dumps({"sidecar": "/tmp/x.py"})}),
+            content_type="application/json",
+        )
+        self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
+        self.assertIn("sidecar", str(response.data["user_args"]))
+        config = ApplicationConfiguration.objects.first()
+        assert config is not None
+        self.assertIsNone(config.user_args)
+
     def test_api_update_config_rejects_invalid_json_objects(self) -> None:
         """
         GIVEN:

src/paperless/config.py

@@ -12,6 +12,17 @@ from paperless.models import ModeChoices
 from paperless.models import OutputTypeChoices
 from paperless.models import RemoteOCRMode
 
+# OCRmyPDF arguments the parser sets itself, pointing into its own temporary
+# directory. The parser reads these files back after OCR, so user supplied
+# values can only break consumption (or write to arbitrary paths), never help.
+OCR_RESERVED_USER_ARGS: frozenset[str] = frozenset(
+    {
+        "input_file_or_options",
+        "output_file",
+        "sidecar",
+    },
+)
+
 
 @dataclasses.dataclass
 class BaseConfig:

src/paperless/parsers/tesseract.py

@@ -21,6 +21,7 @@ from documents.parsers import make_thumbnail_from_pdf
 from documents.utils import copy_file_with_basic_stats
 from documents.utils import maybe_override_pixel_limit
 from documents.utils import remove_alpha_channel
+from paperless.config import OCR_RESERVED_USER_ARGS
 from paperless.config import OcrConfig
 from paperless.models import CleanChoices
 from paperless.models import ModeChoices
@@ -351,7 +352,22 @@ class RasterisedDocumentParser:
 
         if self.settings.user_args is not None:
             try:
-                ocrmypdf_args = {**ocrmypdf_args, **self.settings.user_args}
+                reserved = sorted(
+                    OCR_RESERVED_USER_ARGS & self.settings.user_args.keys(),
+                )
+                if reserved:
+                    self.log.warning(
+                        f"Ignoring OCR user arguments managed by paperless: "
+                        f"{', '.join(reserved)}",
+                    )
+                ocrmypdf_args = {
+                    **ocrmypdf_args,
+                    **{
+                        k: v
+                        for k, v in self.settings.user_args.items()
+                        if k not in OCR_RESERVED_USER_ARGS
+                    },
+                }
             except Exception as e:
                 self.log.warning(
                     f"There is an issue with PAPERLESS_OCR_USER_ARGS, so "

src/paperless/serialisers.py

@@ -19,6 +19,7 @@ from PIL import Image
 from rest_framework import serializers
 from rest_framework.authtoken.serializers import AuthTokenSerializer
 
+from paperless.config import OCR_RESERVED_USER_ARGS
 from paperless.models import ApplicationConfiguration
 from paperless.network import validate_outbound_http_url
 from paperless.validators import reject_dangerous_svg
@@ -251,6 +252,13 @@ class ApplicationConfigurationSerializer(
 
     def validate_user_args(self, value):
         self._require_json_object("user_args", value)
+        if value is not None:
+            reserved = sorted(OCR_RESERVED_USER_ARGS & value.keys())
+            if reserved:
+                raise serializers.ValidationError(
+                    f"user_args may not set arguments managed by paperless: "
+                    f"{', '.join(reserved)}.",
+                )
         return value
 
     def validate_barcode_tag_mapping(self, value):

src/paperless/tests/parsers/test_tesseract_custom_settings.py

@@ -243,6 +243,34 @@ class TestParserSettingsFromDb(DirectoriesMixin, FileSystemAssertsMixin, TestCas
             "UseDeviceIndependentColor",
         )
 
+    def test_ocr_user_args_cannot_override_reserved(self) -> None:
+        """
+        GIVEN:
+            - User arguments which attempt to override arguments the parser
+              manages itself, alongside a legitimate argument
+        WHEN:
+            - OCR parameters are constructed
+        THEN:
+            - Reserved arguments keep the parser supplied values
+            - The legitimate argument is still applied
+        """
+        instance = ApplicationConfiguration.objects.all().first()
+        assert instance is not None
+        instance.user_args = {
+            "sidecar": "/tmp/evil.py",
+            "output_file": "/tmp/out.pdf",
+            "input_file_or_options": "/etc/passwd",
+            "unpaper_args": "--pre-rotate 90",
+        }
+        instance.save()
+
+        params = self.get_params()
+
+        self.assertEqual(params["sidecar"], "sidecar.txt")
+        self.assertEqual(params["output_file"], "output.pdf")
+        self.assertEqual(params["input_file_or_options"], "input.pdf")
+        self.assertEqual(params["unpaper_args"], "--pre-rotate 90")
+
     def test_ocr_user_args(self) -> None:
         """
         GIVEN: