#34209: FileBasedCache has_key is susceptible to race conditions
-------------------------------------+-------------------------------------
Reporter: Marti | Owner: nobody
Raudsepp |
Type: | Status: new
Uncategorized |
Component: Core | Version: 4.1
(Cache system) | Keywords: race, race-
Severity: Normal | condition, FileBasedCache
Triage Stage: | Has patch: 1
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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I received the exception from Django's cache framework:
{{{
FileNotFoundError: [Errno 2] No such file or directory:
'/app/var/cache/d729e4cf4ba88cba5a0f48e0396ec48a.djcache'
[...]
File "django/core/cache/backends/base.py", line 229, in get_or_set
self.add(key, default, timeout=timeout, version=version)
File "django/core/cache/backends/filebased.py", line 26, in add
if self.has_key(key, version):
File "django/core/cache/backends/filebased.py", line 94, in has_key
with open(fname, "rb") as f:
}}}
The code is:
{{{
def has_key(self, key, version=None):
fname = self._key_to_file(key, version)
if os.path.exists(fname):
with open(fname, "rb") as f:
return not self._is_expired(f)
return False
}}}
Between the `exists()` check and `open()`, it's possible for the file to
be deleted. In fact, the `_is_expired()` method itself deletes the file if
it finds it to be expired. So if many threads race to read an expired
cache at once, it's not that unlikely to hit this window.
--
Ticket URL: <https://code.djangoproject.com/ticket/34209>
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