Potential crashes between source deletion and accessing source in the gui

[sssoleileraaa]

Description

If a sync comes back with deleted sources from the server we delete them locally and then call update_sources which will first remove all the source widgets then remove all the conversation widgets for those sources. If a message, reply, or file download job finishes before the source widget is destroyed then it will try to access source.uuid or source.collection in several places in the code and crash the app. I think there is also an issue with a user trying to open a file for the source at this time.

To prevent this type of crash we should only access the source db object when absolutely necessary. For instance, it's not necessary to store source on an object when we only need the uuid so we can find a source widget.

[sssoleileraaa]

Here's a list of areas in the code that need attention regarding possible crashes due to trying to access data on a deleted source without catching the exception:

1. ✔️DONE in delete source widgets for current sync update #1114
   SourceWidget.update raises exception and callers don't catch it causing the app to crash
   • add-source scheduler (STR in add-source scheduler crashes app because of unhandled exception #1117)
   • in the constructor`:

     securedrop-client/securedrop_client/gui/widgets.py

     Line 1175 in f1e935c

     self.update()

2. ✔️DONE in Fix starring behavior #952
   StarToggleButton
3. DeleteSourceMessageBox:

   securedrop-client/securedrop_client/gui/widgets.py

   Line 1414 in f1e935c

   for submission in source.collection:

4. ConversationView:

   securedrop-client/securedrop_client/gui/widgets.py

   Line 3005 in f1e935c

   self.update_conversation(self.source.collection)

5. on_reply_sent:

   securedrop-client/securedrop_client/gui/widgets.py

   Line 3149 in f1e935c

   if source_uuid == self.source.uuid:

6. SourceConversationWrapper:

   securedrop-client/securedrop_client/gui/widgets.py

   Line 3174 in f1e935c

   self.source_uuid = source.uuid

7. on_source_change:

   securedrop-client/securedrop_client/gui/widgets.py

   Line 735 in f1e935c

   self.source_conversations[source.uuid] = conversation_wrapper

8. ✔️DONE in delete source widgets for current sync update #1114
   • uuid in SourceLists.update:

     securedrop-client/securedrop_client/gui/widgets.py

     Line 932 in f1e935c

     source_uuids = [source.uuid for source in sources]

   • last_updated in SourceLists.update when source widgets are reordered (STR in client crashes when sources are reordered #1116)
9. DeleteSourceMessageBox:

   securedrop-client/securedrop_client/gui/widgets.py

   Line 1368 in 78d1bbe

   for submission in source.collection:

10. ReplyBox:

    securedrop-client/securedrop_client/gui/widgets.py

    Line 3271 in 78d1bbe

    if self.source.public_key:

11. SourceProfileShortWidget:

    securedrop-client/securedrop_client/gui/widgets.py

    Line 3650 in f1e935c

    self.updated.setText(_(arrow.get(self.source.last_updated).format('DD MMM')))

12. ✔️DONE in no longer access source db obj in snippet #964
    set_snippet
13. ✔️DONE in delete source widgets for current sync update #1114
    schedule_source_management:

    securedrop-client/securedrop_client/gui/widgets.py

    Line 1005 in 97ce5bb

    self.source_widgets[source.uuid] = new_source

    
    Some of these links take you to areas of the code where there are multiple instances of the issue, so look around for source or file or other database objects widgets are accessing to make sure you get em all. Also I might have missed some in the list above. If you want to fix the issue for now by surrounding the code in a try-catch, that works, but it's more ideal if you can remove the db objects from the widgets.

[sssoleileraaa]

Numbers: 1, 2, and 8 have PRs. The rest are still up for grabs.

[sssoleileraaa]

Saw # 1 crasher in the list happen today:

Traceback (most recent call last):
  File "/home/creviera/workspace/freedomofpress/securedrop-client/securedrop_client/gui/widgets.py", line 1004, in schedule_source_management
    new_source = SourceWidget(self.controller, source)
  File "/home/creviera/workspace/freedomofpress/securedrop-client/securedrop_client/gui/widgets.py", line 1220, in __init__
    self.update()
  File "/home/creviera/workspace/freedomofpress/securedrop-client/securedrop_client/gui/widgets.py", line 1227, in update
    self.controller.session.refresh(self.source)
  File "/home/creviera/workspace/freedomofpress/securedrop-client/.venv/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 1675, in refresh
    "Could not refresh instance '%s'" % instance_str(instance)
sqlalchemy.exc.InvalidRequestError: Could not refresh instance '<Source at 0x7f04fd010790>'

[eloquence]

We discussed today that a naive try/catch strategy around all UI access to widgets that may be tied to deleted database objects is probably the best first iteration to safeguard this. We'll likely not get to this before Monday, but it's one of the highest priority known areas that can cause crashes, so tracking as release blocker.