Silently closes UDP socket #338

spumer · 2020-04-27T08:49:29Z

uvloop version: 0.14
Python version: 3.8.2
Platform: Linux
Can you reproduce the bug with PYTHONASYNCIODEBUG in env?: Yes
Does uvloop behave differently from vanilla asyncio? How?: Yes. See below

uvloop silently closes UDP socket when sending data to incorrect destination.

Test program:

import asyncio
import uvloop

# uncomment this line to check it with uvloop
#uvloop.install()


async def main():
    loop = asyncio.get_event_loop()
    transport, proto = await loop.create_datagram_endpoint(
        asyncio.DatagramProtocol,
        local_addr=("192.168.0.2", 0),
    )
    print(transport.get_extra_info('sockname'))
    print("Before sending the message with None destination")
    transport.sendto(b"deadbeef")
    print("After sending the message with None destination")
    
    await asyncio.sleep(0.1)  # let asyncio closes internal socket

    print("Before sending the message with incorrect port destination")
    transport.sendto(b"deadbeef", ("45.83.128.251", 0))
    print("After sending the message with incorrect port destination")
    transport.close()


asyncio.get_event_loop().run_until_complete(main())

asyncio output:

'192.168.0.2', 59471) Before sending the message with None destination Fatal write error on datagram transport protocol: transport: <_SelectorDatagramTransport fd=6 read=polling write=> Traceback (most recent call last): File "/root/.pyenv/versions/3.8.2/lib/python3.8/asyncio/selector_events.py", line 1046, in sendto self._sock.sendto(data, addr) TypeError: sendto(): AF_INET address must be tuple, not NoneType After sending the message with None destination Before sending the message with incorrect port destination Traceback (most recent call last): File "/root/.pyenv/versions/3.8.2/lib/python3.8/asyncio/selector_events.py", line 1046, in sendto self._sock.sendto(data, addr) AttributeError: 'NoneType' object has no attribute 'sendto'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "", line 1, in
File "/root/.pyenv/versions/3.8.2/lib/python3.8/asyncio/base_events.py", line 616, in run_until_complete
return future.result()
File "", line 14, in main
File "/root/.pyenv/versions/3.8.2/lib/python3.8/asyncio/selector_events.py", line 1056, in sendto
self._fatal_error(
File "/root/.pyenv/versions/3.8.2/lib/python3.8/asyncio/selector_events.py", line 703, in _fatal_error
self._loop.call_exception_handler({
AttributeError: 'NoneType' object has no attribute 'call_exception_handler'

uvloop output:

('192.168.0.2', 33515) Before sending the message with None destination After sending the message with None destination Before sending the message with incorrect port destination After sending the message with incorrect port destination

Then we can cut off first block with sending to None destination. And here we have NEW ONE differece in handling ip:port.

async def main():
    loop = asyncio.get_event_loop()
    transport, proto = await loop.create_datagram_endpoint(
        asyncio.DatagramProtocol,
        local_addr=("192.168.0.2", 0),
    )
    print(transport.get_extra_info('sockname'))
    print("Please use `netstat -au` to see this socket really listening. I will wait 10 sec")
    await asyncio.sleep(10)
    
    print("Before sending the message with incorrect port destination")
    transport.sendto(b"deadbeef", ("45.83.128.251", 0))
    print("After sending the message with incorrect port destination")

    print("Please use `netstat -au` to see this socket STILL really listening. I will wait 10 sec")
    await asyncio.sleep(10)

    transport.close()

When i run it with asyncio event loop all looks fine, socket still present.

When i run it with uvloop it silently closes, and also i can go into infinity wait on recv() call

As i know RFC describe that case as (https://tools.ietf.org/html/rfc8085#section-5.1):

A UDP sender SHOULD NOT use a source port value of zero.  A source
   port number that cannot be easily determined from the address or
   payload type provides protection at the receiver from data injection
   attacks by off-path devices.  A UDP receiver SHOULD NOT bind to port
   zero.

But i got real messages from the internet with that port. I will drop it in my application, but i think uvloop should not silently closes socket. It's very unexpected and differ from asyncio event loop.

Proof from Sentry (https://github.com/spumer/source-query-proxy):

next iteration of recv packet was failed, cause in previous we send response to zero port


        fix(proxy): no random stuck anymore

App can start infinity waiting on silently closed socket. This behaviour possible due uvloop internal bug MagicStack/uvloop#338

spumer added a commit to spumer/source-query-proxy that referenced this issue Jun 17, 2020

fix(proxy): no random stuck anymore

f3dff0b

App can start infinity waiting on silently closed socket. This behaviour possible due uvloop internal bug MagicStack/uvloop#338

MagicStack / uvloop

Silently closes UDP socket #338

Silently closes UDP socket #338

spumer commented Apr 27, 2020

MagicStack / uvloop

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Silently closes UDP socket #338

Silently closes UDP socket #338

Comments

spumer commented Apr 27, 2020