id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
34209	FileBasedCache has_key is susceptible to race conditions	Marti Raudsepp	nobody	"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.
"	Uncategorized	new	Core (Cache system)	4.1	Normal		race, race-condition, FileBasedCache		Unreviewed	1	0	0	0	0	0