[Django] #29471: Set-Cookie response is cached for deleting invalid session cookies
Django
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Reporter: Duane | Owner: nobody
Hutchins |
Type: Bug | Status: new
Component: | Version: 2.0
contrib.sessions |
Severity: Normal | Keywords: empty session cache
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Regarding:
[https://docs.djangoproject.com/en/2.0/_modules/django/contrib/sessions/middleware/#SessionMiddleware
django.contrib.sessions.middleware.SessionMiddleware]
and
[https://docs.djangoproject.com/en/2.0/_modules/django/utils/cache/#learn_cache_key
django.utils.cache]
Using the SessionMiddleware and caching, if an invalid sessionid (i.e. an
empty session) is passed via cookie, the SessionMiddleware responds by
deleting the cookie, and this response is cached without Vary: Cookie, so
all subsequent authenticated requests also receive that delete-session-
cookie header.
The end result is that if a cache-enabled page receives a request using an
invalid session id, that page will log out all users who visit that page
until that cache expires/purges.
To duplicate:
* Enable caching and sessions as normal.
* Visit a cache-enabled page which shows different content for users who
are logged in vs not logged in.
* Log in via browser
* Change your browser's sessionid cookie value via Chrome Developer Tools
or whatever.
* Refresh your browser
* The browser is told to delete the invalid cookie (correct).
* Log in again. Refresh again (if necessary).
* The login is successful, however, the browser is instructed to delete
the session cookie (incorrect).
* The user is logged out
* The same logout happens for all users visit that page -- until cache
expires
If I decorate the aforementioned page view with @vary_on_cookie (which
inserts the Vary:Cookie header), then the issue is resolved.
Possible solutions I can think of:
* SessionMiddleware adds Vary:Cookie when deleting invalid session cookies
* Cache Util assumes Vary:Cookie when response includes Set-Cookie header.
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Ticket URL: <https://code.djangoproject.com/ticket/29471>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
Django
-------------------------------------+-------------------------------------
Type: Bug | Status: new
Component: contrib.sessions | Version: 2.0
Severity: Normal | Resolution:
Keywords: empty session cache | Triage Stage:
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Tim Graham):
Isn't the solution to use `@vary_on_cookie` as you said? If you have "a
cache-enabled page which shows different content for users who are logged
in vs not logged in" then you need to use the `Vary: Cookie` header, don't
you?
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Ticket URL: <https://code.djangoproject.com/ticket/29471#comment:1>
Django
-------------------------------------+-------------------------------------
Type: Bug | Status: new
Component: contrib.sessions | Version: 2.0
Severity: Normal | Resolution:
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Duane Hutchins):
Replying to [comment:1 Tim Graham]:
> Isn't the solution to use `@vary_on_cookie` as you said? If you have "a
cache-enabled page which shows different content for users who are logged
in vs not logged in" then you need to use the `Vary: Cookie` header, don't
you?
The SessionMiddleware sets `Vary: Cookie` automatically if the session is
accessed. The bug is that SessionMiddleware is not doing that if the
session cookie is invalid.
When accessing the session object:
* No session cookie => `Vary: Cookie` is set
* Valid session cookie => `Vary: Cookie` is set
* Invalid session cookie => `Vary: Cookie` is not set
Examining
[https://docs.djangoproject.com/en/2.0/_modules/django/contrib/sessions/middleware/#SessionMiddleware
the source code], you can confirm this as true because the
`patch_vary_headers` only happens if the session cookie is valid or
missing.
{{{
# First check if we need to delete this cookie.
# The session should be deleted only if the session is
entirely empty
if settings.SESSION_COOKIE_NAME in request.COOKIES and empty:
response.delete_cookie(
settings.SESSION_COOKIE_NAME,
path=settings.SESSION_COOKIE_PATH,
domain=settings.SESSION_COOKIE_DOMAIN,
)
else:
if accessed:
patch_vary_headers(response, ('Cookie',))
}}}
The end result is that this causes the cache handler to cache invalid-
session responses without `Vary: Cookie`. So, if the cached invalid-
session response was to delete the session cookie, then the cookie is
always deleted on that page -- until the cache is updated.
--
Ticket URL: <https://code.djangoproject.com/ticket/29471#comment:2>
Django
-------------------------------------+------------------------------------
Component: contrib.sessions | Version: 2.0
Severity: Normal | Resolution:
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+------------------------------------
* stage: Unreviewed => Accepted
--
Ticket URL: <https://code.djangoproject.com/ticket/29471#comment:3>
Django
Reporter: Duane Hutchins | Owner: nobody
Component: contrib.sessions | Version: 2.0
Severity: Normal | Resolution:
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+------------------------------------
* cc: Herbert Fortes (added)
--
Ticket URL: <https://code.djangoproject.com/ticket/29471#comment:4>
Django
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| birthdaysgift
Type: Bug | Status: assigned
Component: contrib.sessions | Version: 2.0
Severity: Normal | Resolution:
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* owner: nobody => birthdaysgift
* status: new => assigned
--
Ticket URL: <https://code.djangoproject.com/ticket/29471#comment:5>
Django
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| birthdaysgift
Type: Bug | Status: assigned
Component: contrib.sessions | Version: 2.0
Severity: Normal | Resolution:
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* has_patch: 0 => 1
--
Ticket URL: <https://code.djangoproject.com/ticket/29471#comment:6>
Django
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| birthdaysgift
Type: Bug | Status: assigned
Component: contrib.sessions | Version: 2.0
Severity: Normal | Resolution:
| checkin
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* stage: Accepted => Ready for checkin
--
Ticket URL: <https://code.djangoproject.com/ticket/29471#comment:7>
Django
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| birthdaysgift
Component: contrib.sessions | Version: 2.0
Severity: Normal | Resolution: fixed
Keywords: empty session cache | Triage Stage: Ready for
| checkin
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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* status: assigned => closed
* resolution: => fixed
Comment:
In [changeset:"dc740dde50873e82f761386fd73ca17d9eaa008b" dc740dd]:
{{{
#!CommitTicketReference repository=""
revision="dc740dde50873e82f761386fd73ca17d9eaa008b"
Fixed #29471 -- Added 'Vary: Cookie' to invalid/empty session cookie
responses.
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/29471#comment:8>
Django
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| birthdaysgift
Type: Bug | Status: closed
Component: contrib.sessions | Version: 2.0
Severity: Normal | Resolution: fixed
Keywords: empty session cache | Triage Stage: Ready for
| checkin
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* cc: Martin H. (added)
Comment:
AFAICS, this bug is already present in the 2.x versions. Shouldn't it be
patched there as well?
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Ticket URL: <https://code.djangoproject.com/ticket/29471#comment:9>
Django
-------------------------------------+-------------------------------------
| birthdaysgift
Type: Bug | Status: closed
Component: contrib.sessions | Version: 2.0
Severity: Normal | Resolution: fixed
Keywords: empty session cache | Triage Stage: Ready for
| checkin
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by felixxm):
This patch doesn't qualify for a backport, because it's not a regression
or a new feature in Django 2.2.
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Ticket URL: <https://code.djangoproject.com/ticket/29471#comment:10>