Fix download from UploadedFileWidget in backend

src/pretix/base/forms/questions.py

@@ -758,7 +758,7 @@ class BaseQuestionsForm(forms.Form):
                     label=label, required=required,
                     help_text=help_text,
                     initial=initial.file if initial else None,
-                    widget=PortraitImageWidget(answer=initial,
+                    widget=PortraitImageWidget(answer=initial, request=request,
                                                attrs={'data-portrait-photo': 'true'}),
                 )
             else:
@@ -766,7 +766,7 @@ class BaseQuestionsForm(forms.Form):
                     label=label, required=required,
                     help_text=help_text,
                     initial=initial.file if initial else None,
-                    widget=UploadedFileWidget(answer=initial),
+                    widget=UploadedFileWidget(answer=initial, request=request),
                     ext_whitelist=settings.FILE_UPLOAD_EXTENSIONS_OTHER,
                     max_size=settings.FILE_UPLOAD_MAX_SIZE_OTHER,
                 )

src/pretix/base/forms/widgets.py

@@ -47,6 +47,7 @@ from pretix.helpers.i18n import (
     get_format_without_seconds, get_javascript_format,
     get_javascript_format_without_seconds,
 )
+from pretix.helpers.safedownload import get_token
 
 
 def replace_arabic_numbers(inp):
@@ -158,19 +159,25 @@ class TimePickerWidget(forms.TimeInput):
 class UploadedFileWidget(forms.ClearableFileInput):
     def __init__(self, *args, **kwargs):
         self.answer = kwargs.pop('answer')
+        self.request = kwargs.pop('request')
         super().__init__(*args, **kwargs)
 
     class FakeFile:
-        def __init__(self, file, answer):
+        def __init__(self, file, answer, request):
             self.file = file
             self.answer = answer
+            self.request = request
 
         def __str__(self):
             return os.path.basename(self.file.name).split('.', 1)[-1]
 
         @property
         def url(self):
-            return self.answer.frontend_file_url
+            token = get_token(self.request, self.answer)
+            if self.request.resolver_match.namespace == 'control':
+                return self.answer.backend_file_url + '?token=' + token
+            else:
+                return self.answer.frontend_file_url + '?token=' + token
 
     def get_context(self, name, value, attrs):
         # Browsers can't recognize that the server already has a file uploaded
@@ -183,7 +190,7 @@ class UploadedFileWidget(forms.ClearableFileInput):
 
     def format_value(self, value):
         if self.is_initial(value):
-            return self.FakeFile(value, self.answer)
+            return self.FakeFile(value, self.answer, self.request)
 
 
 class SplitDateTimePickerWidget(forms.SplitDateTimeWidget):

src/pretix/helpers/safedownload.py

@@ -24,17 +24,21 @@ import hashlib
 from django.core.signing import BadSignature, TimestampSigner
 
 
+class SafeDownloadSigner(TimestampSigner):
+    pass
+
+
 def get_token(request, answer):
     if not request.session.session_key:
         request.session.create()
     payload = '{}:{}'.format(request.session.session_key, answer.pk)
-    signer = TimestampSigner()
+    signer = SafeDownloadSigner()
     return signer.sign(hashlib.sha1(payload.encode()).hexdigest())
 
 
 def check_token(request, answer, token):
     payload = hashlib.sha1('{}:{}'.format(request.session.session_key, answer.pk).encode()).hexdigest()
-    signer = TimestampSigner()
+    signer = SafeDownloadSigner()
     try:
         return payload == signer.unsign(token, max_age=3600 * 24)
     except BadSignature:

src/pretix/presale/views/cart.py

@@ -67,6 +67,7 @@ from pretix.base.services.cart import (
 from pretix.base.timemachine import time_machine_now
 from pretix.base.views.tasks import AsyncAction
 from pretix.helpers.http import redirect_to_url
+from pretix.helpers.safedownload import check_token
 from pretix.multidomain.urlreverse import eventreverse
 from pretix.presale.productlist import (
     item_group_by_category, prepare_item_list_for_shop,
@@ -848,6 +849,7 @@ class RedeemView(NoSearchIndexViewMixin, EventViewMixin, CartMixin, TemplateView
 class AnswerDownload(EventViewMixin, View):
     def get(self, request, *args, **kwargs):
         answid = kwargs.get('answer')
+        token = request.GET.get('token', '')
         cart_id = get_or_create_cart_id(self.request)
         answer = get_object_or_404(
             QuestionAnswer,
@@ -856,8 +858,10 @@ class AnswerDownload(EventViewMixin, View):
         )
         if not answer.file:
             return Http404()
+        if not check_token(request, answer, token):
+            raise Http404(_("This link is no longer valid. Please go back, refresh the page, and try again."))
 
-        ftype, _ = mimetypes.guess_type(answer.file.name)
+        ftype, _1 = mimetypes.guess_type(answer.file.name)
         filename = '{}-cart-{}'.format(
             self.request.event.slug.upper(),
             os.path.basename(answer.file.name).split('.', 1)[1]
@@ -865,6 +869,7 @@ class AnswerDownload(EventViewMixin, View):
         resp = FileResponse(
             answer.file,
             filename=filename,
+            as_attachment=True,
             content_type=ftype or 'application/binary'
         )
         return resp