Check that uploaded images are actually images

core/schemas.py

@@ -1,16 +1,29 @@
 from pathlib import Path
-from typing import Annotated
+from typing import Annotated, Any
 
 from annotated_types import MinLen
 from django.contrib.staticfiles.storage import staticfiles_storage
 from django.db.models import Q
 from django.urls import reverse
 from django.utils.text import slugify
+from django.utils.translation import gettext as _
 from haystack.query import SearchQuerySet
-from ninja import FilterSchema, ModelSchema, Schema
+from ninja import FilterSchema, ModelSchema, Schema, UploadedFile
 from pydantic import AliasChoices, Field
+from pydantic_core.core_schema import ValidationInfo
 
 from core.models import Group, SithFile, User
+from core.utils import is_image
+
+
+class UploadedImage(UploadedFile):
+    @classmethod
+    def _validate(cls, v: Any, info: ValidationInfo) -> Any:
+        super()._validate(v, info)
+        if not is_image(v):
+            msg = _("This file is not a valid image")
+            raise ValueError(msg)
+        return v
 
 
 class SimpleUserSchema(ModelSchema):

core/utils.py

@@ -22,6 +22,7 @@ from typing import Final
 import PIL
 from django.conf import settings
 from django.core.files.base import ContentFile
+from django.core.files.uploadedfile import UploadedFile
 from django.http import HttpRequest
 from django.utils.timezone import localdate
 from PIL import ExifTags
@@ -111,6 +112,18 @@ def get_semester_code(d: date | None = None) -> str:
     return "P" + str(start.year)[-2:]
 
 
+def is_image(file: UploadedFile):
+    try:
+        im = PIL.Image.open(file.file)
+        im.verify()
+        # go back to the start of the file, without closing it.
+        # Otherwise, further checks on django side will fail
+        file.seek(0)
+    except PIL.UnidentifiedImageError:
+        return False
+    return True
+
+
 def resize_image(
     im: Image, edge: int, img_format: str, *, optimize: bool = True
 ) -> ContentFile: