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Race condition in BaseConnector leads to exceeding connection limit #4936

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PandaWill opened this issue Aug 26, 2020 · 1 comment
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Race condition in BaseConnector leads to exceeding connection limit #4936

PandaWill opened this issue Aug 26, 2020 · 1 comment
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@PandaWill
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馃悶 Describe the bug
It is possible for BaseConnector to exceed the limited number of connections. This is a result of a race condition/TOC-TOU bug on the available connections.

The bug arises from the following situation:

bc = BaseConnector(limit=1)

con1 = bc.connect(...) # makes first connection
con2 = bc.connect(...) # joins waiters queue
con1.release( ) # releases connection
con3 = bc.connect(...) # takes available connection
# con2 is resumed because of `set_result` call and creates second connection
...
con2.release()
con3.release()

Note that the bug is only present if connection 3 is initiated before connection 2 resumes. The ordering of these two events is non-deterministic.

In Depth
When releasing a connection, _release_waiter will check that there is an available connection and call set_result to mark the future as done. This is assuming that this task will be resumed immediately but this isn't always the case: https://github.com/aio-libs/aiohttp/blob/3.7/aiohttp/connector.py#L588

If a coroutine is ran that calls connect, it will find there is an available connection and take it.
This will drop the key from BaseConnect._conns as it has taken the last connection: https://github.com/aio-libs/aiohttp/blob/3.7/aiohttp/connector.py#L569

If the future (triggered by set_result) now resumes, then proto = self._get(key) will be None, because the key was deleted above. Hence it will now create a new connection object.
https://github.com/aio-libs/aiohttp/blob/3.7/aiohttp/connector.py#L512

We have now created a second connection when limit was set to 1.

馃挕 To Reproduce
See pull request containing failing unit test.

馃挕 Expected behavior
Limit is observed appropriately

馃搵 Logs/tracebacks

馃搵 Your version of the Python
3.8.2

馃搵 Your version of the aiohttp/yarl/multidict distributions
Name: aiohttp
Version: 3.6.2

Name: multidict
Version: 4.7.6

Name: yarl
Version: 1.5.1
@PandaWill PandaWill added the bug label Aug 26, 2020
@PandaWill PandaWill mentioned this issue Aug 26, 2020
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@PandaWill PandaWill changed the title Race condition in BaseConnector leads to breaking connection limit Race condition in BaseConnector leads to exceeding connection limit Aug 27, 2020
@patchback patchback bot mentioned this issue Oct 15, 2020
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@PandaWill
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PandaWill commented Oct 15, 2020 •
edited

Fixed by #4937 and #5047

netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this issue Oct 24, 2020
@Midar
Update www/py-aiohttp to 3.7.0
fe4dd20 
This fixes py-yarl in pkgsrc being too new for py-aiohttp.


3.7.0 (2020-10-24)
==================

Features
--------

- Response headers are now prepared prior to running ``on_response_prepare`` hooks, directly before headers are sent to the client.
  `#1958 <https://github.com/aio-libs/aiohttp/issues/1958>`_
- Add a ``quote_cookie`` option to ``CookieJar``, a way to skip quotation wrapping of cookies containing special characters.
  `#2571 <https://github.com/aio-libs/aiohttp/issues/2571>`_
- Call ``AccessLogger.log`` with the current exception available from ``sys.exc_info()``.
  `#3557 <https://github.com/aio-libs/aiohttp/issues/3557>`_
- `web.UrlDispatcher.add_routes` and `web.Application.add_routes` return a list
  of registered `AbstractRoute` instances. `AbstractRouteDef.register` (and all
  subclasses) return a list of registered resources registered resource.
  `#3866 <https://github.com/aio-libs/aiohttp/issues/3866>`_
- Added properties of default ClientSession params to ClientSession class so it is available for introspection
  `#3882 <https://github.com/aio-libs/aiohttp/issues/3882>`_
- Don't cancel web handler on peer disconnection, raise `OSError` on reading/writing instead.
  `#4080 <https://github.com/aio-libs/aiohttp/issues/4080>`_
- Implement BaseRequest.get_extra_info() to access a protocol transports' extra info.
  `#4189 <https://github.com/aio-libs/aiohttp/issues/4189>`_
- Added `ClientSession.timeout` property.
  `#4191 <https://github.com/aio-libs/aiohttp/issues/4191>`_
- allow use of SameSite in cookies.
  `#4224 <https://github.com/aio-libs/aiohttp/issues/4224>`_
- Use ``loop.sendfile()`` instead of custom implementation if available.
  `#4269 <https://github.com/aio-libs/aiohttp/issues/4269>`_
- Apply SO_REUSEADDR to test server's socket.
  `#4393 <https://github.com/aio-libs/aiohttp/issues/4393>`_
- Use .raw_host instead of slower .host in client API
  `#4402 <https://github.com/aio-libs/aiohttp/issues/4402>`_
- Allow configuring the buffer size of input stream by passing ``read_bufsize`` argument.
  `#4453 <https://github.com/aio-libs/aiohttp/issues/4453>`_
- Pass tests on Python 3.8 for Windows.
  `#4513 <https://github.com/aio-libs/aiohttp/issues/4513>`_
- Add `method` and `url` attributes to `TraceRequestChunkSentParams` and `TraceResponseChunkReceivedParams`.
  `#4674 <https://github.com/aio-libs/aiohttp/issues/4674>`_
- Add ClientResponse.ok property for checking status code under 400.
  `#4711 <https://github.com/aio-libs/aiohttp/issues/4711>`_
- Don't ceil timeouts that are smaller than 5 seconds.
  `#4850 <https://github.com/aio-libs/aiohttp/issues/4850>`_
- TCPSite now listens by default on all interfaces instead of just IPv4 when `None` is passed in as the host.
  `#4894 <https://github.com/aio-libs/aiohttp/issues/4894>`_
- Bump ``http_parser`` to 2.9.4
  `#5070 <https://github.com/aio-libs/aiohttp/issues/5070>`_


Bugfixes
--------

- Fix keepalive connections not being closed in time
  `#3296 <https://github.com/aio-libs/aiohttp/issues/3296>`_
- Fix failed websocket handshake leaving connection hanging.
  `#3380 <https://github.com/aio-libs/aiohttp/issues/3380>`_
- Fix tasks cancellation order on exit. The run_app task needs to be cancelled first for cleanup hooks to run with all tasks intact.
  `#3805 <https://github.com/aio-libs/aiohttp/issues/3805>`_
- Don't start heartbeat until _writer is set
  `#4062 <https://github.com/aio-libs/aiohttp/issues/4062>`_
- Fix handling of multipart file uploads without a content type.
  `#4089 <https://github.com/aio-libs/aiohttp/issues/4089>`_
- Preserve view handler function attributes across middlewares
  `#4174 <https://github.com/aio-libs/aiohttp/issues/4174>`_
- Fix the string representation of ``ServerDisconnectedError``.
  `#4175 <https://github.com/aio-libs/aiohttp/issues/4175>`_
- Raising RuntimeError when trying to get encoding from not read body
  `#4214 <https://github.com/aio-libs/aiohttp/issues/4214>`_
- Remove warning messages from noop.
  `#4282 <https://github.com/aio-libs/aiohttp/issues/4282>`_
- Raise ClientPayloadError if FormData re-processed.
  `#4345 <https://github.com/aio-libs/aiohttp/issues/4345>`_
- Fix a warning about unfinished task in ``web_protocol.py``
  `#4408 <https://github.com/aio-libs/aiohttp/issues/4408>`_
- Fixed 'deflate' compression. According to RFC 2616 now.
  `#4506 <https://github.com/aio-libs/aiohttp/issues/4506>`_
- Fixed OverflowError on platforms with 32-bit time_t
  `#4515 <https://github.com/aio-libs/aiohttp/issues/4515>`_
- Fixed request.body_exists returns wrong value for methods without body.
  `#4528 <https://github.com/aio-libs/aiohttp/issues/4528>`_
- Fix connecting to link-local IPv6 addresses.
  `#4554 <https://github.com/aio-libs/aiohttp/issues/4554>`_
- Fix a problem with connection waiters that are never awaited.
  `#4562 <https://github.com/aio-libs/aiohttp/issues/4562>`_
- Always make sure transport is not closing before reuse a connection.

  Reuse a protocol based on keepalive in headers is unreliable.
  For example, uWSGI will not support keepalive even it serves a
  HTTP 1.1 request, except explicitly configure uWSGI with a
  ``--http-keepalive`` option.

  Servers designed like uWSGI could cause aiohttp intermittently
  raise a ConnectionResetException when the protocol poll runs
  out and some protocol is reused.
  `#4587 <https://github.com/aio-libs/aiohttp/issues/4587>`_
- Handle the last CRLF correctly even if it is received via separate TCP segment.
  `#4630 <https://github.com/aio-libs/aiohttp/issues/4630>`_
- Fix the register_resource function to validate route name before splitting it so that route name can include python keywords.
  `#4691 <https://github.com/aio-libs/aiohttp/issues/4691>`_
- Improve typing annotations for ``web.Request``, ``aiohttp.ClientResponse`` and
  ``multipart`` module.
  `#4736 <https://github.com/aio-libs/aiohttp/issues/4736>`_
- Fix resolver task is not awaited when connector is cancelled
  `#4795 <https://github.com/aio-libs/aiohttp/issues/4795>`_
- Fix a bug "Aiohttp doesn't return any error on invalid request methods"
  `#4798 <https://github.com/aio-libs/aiohttp/issues/4798>`_
- Fix HEAD requests for static content.
  `#4809 <https://github.com/aio-libs/aiohttp/issues/4809>`_
- Fix incorrect size calculation for memoryview
  `#4890 <https://github.com/aio-libs/aiohttp/issues/4890>`_
- Add HTTPMove to _all__.
  `#4897 <https://github.com/aio-libs/aiohttp/issues/4897>`_
- Fixed the type annotations in the ``tracing`` module.
  `#4912 <https://github.com/aio-libs/aiohttp/issues/4912>`_
- Fix typing for multipart ``__aiter__``.
  `#4931 <https://github.com/aio-libs/aiohttp/issues/4931>`_
- Fix for race condition on connections in BaseConnector that leads to exceeding the connection limit.
  `#4936 <https://github.com/aio-libs/aiohttp/issues/4936>`_
- Add forced UTF-8 encoding for ``application/rdap+json`` responses.
  `#4938 <https://github.com/aio-libs/aiohttp/issues/4938>`_
- Fix inconsistency between Python and C http request parsers in parsing pct-encoded URL.
  `#4972 <https://github.com/aio-libs/aiohttp/issues/4972>`_
- Fix connection closing issue in HEAD request.
  `#5012 <https://github.com/aio-libs/aiohttp/issues/5012>`_
- Fix type hint on BaseRunner.addresses (from ``List[str]`` to ``List[Any]``)
  `#5086 <https://github.com/aio-libs/aiohttp/issues/5086>`_
- Make `web.run_app()` more responsive to Ctrl+C on Windows for Python < 3.8. It slightly
  increases CPU load as a side effect.
  `#5098 <https://github.com/aio-libs/aiohttp/issues/5098>`_


Improved Documentation
----------------------

- Fix example code in client quick-start
  `#3376 <https://github.com/aio-libs/aiohttp/issues/3376>`_
- Updated the docs so there is no contradiction in ``ttl_dns_cache`` default value
  `#3512 <https://github.com/aio-libs/aiohttp/issues/3512>`_
- Add 'Deploy with SSL' to docs.
  `#4201 <https://github.com/aio-libs/aiohttp/issues/4201>`_
- Change typing of the secure argument on StreamResponse.set_cookie from ``Optional[str]`` to ``Optional[bool]``
  `#4204 <https://github.com/aio-libs/aiohttp/issues/4204>`_
- Changes ``ttl_dns_cache`` type from int to Optional[int].
  `#4270 <https://github.com/aio-libs/aiohttp/issues/4270>`_
- Simplify README hello word example and add a documentation page for people coming from requests.
  `#4272 <https://github.com/aio-libs/aiohttp/issues/4272>`_
- Improve some code examples in the documentation involving websockets and starting a simple HTTP site with an AppRunner.
  `#4285 <https://github.com/aio-libs/aiohttp/issues/4285>`_
- Fix typo in code example in Multipart docs
  `#4312 <https://github.com/aio-libs/aiohttp/issues/4312>`_
- Fix code example in Multipart section.
  `#4314 <https://github.com/aio-libs/aiohttp/issues/4314>`_
- Update contributing guide so new contributors read the most recent version of that guide. Update command used to create test coverage reporting.
  `#4810 <https://github.com/aio-libs/aiohttp/issues/4810>`_
- Spelling: Change "canonize" to "canonicalize".
  `#4986 <https://github.com/aio-libs/aiohttp/issues/4986>`_
- Add ``aiohttp-sse-client`` library to third party usage list.
  `#5084 <https://github.com/aio-libs/aiohttp/issues/5084>`_


Misc
----

- `#2856 <https://github.com/aio-libs/aiohttp/issues/2856>`_, `#4218 <https://github.com/aio-libs/aiohttp/issues/4218>`_, `#4250 <https://github.com/aio-libs/aiohttp/issues/4250>`_
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