csrfmiddleware sometimes raises IOError via _load_post_and_files

[Walter Doekes]

Hi,

according the recently closed #12250, process_view middleware is not supposed to raise exceptions.

The documentation already states:
"""Accessing request.POST ... from process_request or process_view ... should normally be avoided."""
​https://docs.djangoproject.com/en/dev/topics/http/middleware/#process-view

And here is another reason:

Sometimes the connection is reset/lost during HTTP request (during post/file data upload): an IOError is generated when read()ing from the data stream (from _load_post_and_files()).

Since the CsrfViewMiddleware attempts to get the csrfmiddlewaretoken from the POST data, the exception is propagated from there. And it's unhandleable, since we cannot catch exceptions from process_view().

The attached test simulates the situation by simply raising an IOError when an attempt to access POST is done. The attached patch silently ignores the IOError and treats it as if an empty csrfmiddleware token was supplied.

Regards,
Walter Doekes

P.S. Reproducing the IOError (for the generic non-csrf case) in the wild was trivial with apache2+mod_wsgi, but harder on nginx+uwsgi. For the former it was a matter of killing the netcat after feeding it a large-ish amount of multipart/form-data.

[Tim Graham <timograham@…>]

In 815e7a57216b3e6ef716e924016acb09633ea8d1:

Fixed #20128 -- Made CsrfViewMiddleware ignore IOError when reading POST data.

Thanks Walter Doekes.