Opened 4 weeks ago

Last modified 2 days ago

#26412 new defect

KeyError in can_exit_to caused by lru_cache

Reported by: juga Owned by: atagar
Priority: Medium Milestone:
Component: Core Tor/Stem Version:
Severity: Normal Keywords: tor-bwauth
Cc: pastly Actual Points:
Parent ID: Points:
Reviewer: Sponsor:

Description (last modified by juga)

As pastly reported in,
stem giving this traceback:

File "/home/pastly/src/simple-bw-scanner/venv-editable/lib/python3.5/site-packages/stem/", line 285, in can_exit_to

if not self.is_exiting_allowed():KeyError: (<stem.exit_policy.MicroExitPolicy object at 0x7f8de6438ba8>,)

Apparently caused by  a Python bug with lru_cache.

pastly is already trying to find out which Python versions fail, to use stem's lru_cache for those ones.

This ticket blocks #26848

Edit: blocks ticket

Child Tickets

Change History (7)

comment:1 Changed 4 weeks ago by juga

Keywords: tor-bwauth added

comment:2 Changed 4 weeks ago by pastly

I'm running a little toy script that kinda sorta behaves like sbws in hopes that I can reproduce this. I have been doing so for 24 hours or so now.

I'm also running sbws 0.4.2-dev through a very limited Tor client with BandwidthRate 500 KBytes set, and have been doing so for 24 hours.

I'm doing all of this with Python 3.4.8, 3.5.3, and 3.6.5.

I will do this for a few more days. If I don't get these errors, I will switch sbws to the version it was at when these KeyErrors were happening. Of note, at that time we were getting exit policies from micro descriptors but now we get them from server descriptors.

comment:3 Changed 3 weeks ago by atagar

Status: newneeds_information

Thanks juga, thanks pastly! Gonna swap this ticket's status. Feel free to toggle it back when there's something for us to do on the Stem front.

comment:4 Changed 2 weeks ago by pastly

This bug doesn't reveal itself when descriptors are used. Just microdescriptors. Therefore sbws no longer has this bug.

I switched to sbws 0.4.0 which hits this bug.

3.5.2 and 3.5.3 hit it essentially immediately. 3.5.4 does not within 2 hours.

I'll check if anything in 3.4.X or 3.6.X is affected.

comment:5 Changed 9 days ago by pastly

Status: needs_informationnew

sbws version 0.4.0
stem version 1.6.0-dev at 0192b29a4784465e5f69f11ced584a54644e4a90

See below for tested versions.

matt@play:~/src$ grep -c KeyError dotsbws-3*/debug.scanner.log

The huge difference in the numbers is because I ran these for vastly different amounts of time. 3.5.1 is not 3 orders of magnitude more buggy than 3.5.0. 3.5.4 ran for 24 hours and didn't display the issue; 3.5.0 ran for 2 minutes and displayed the issue.

Example unhelpful traceback that the above grep is searching for.

[2018-07-10 10:42:47,961] [sbws.lib.relaylist] [ERROR] Got that KeyError in stem again...: (<stem.exit_policy.ExitPolicy object at 0x7f9fe6f656d8>, <object object at 0x7fa01e24b080>, ('port', 80))
Traceback (most recent call last):
  File "/home/matt/src/simple-bw-scanner/sbws/lib/", line 167, in exits_can_exit_to
    if policy is not None and policy.can_exit_to(port=port):

atagar: based on these findings I recommend using stem's lru_cache for python 3.5.0-3.5.3. Or ... figuring out why getting exit policies from microdescriptors doesn't play nicely with python's lru_cache in only a couple versions of python.

Switching back to new because I no longer think this needs_information.

comment:6 Changed 5 days ago by juga

In case it is useful, i paste traceback lines including the lines where the exception is raised in stem (python 3.5.3):

  File "/path/simple-bw-scanner/sbws/lib/", line 120, in can_exit_to
    return self.exit_policy.can_exit_to(host, port)
  File "/path/.virtualenvs/simplebwscanner3/lib/python3.5/site-packages/stem-1.6.0.dev0-py3.5.egg/stem/", line 294, in can_exit_to
    if rule.is_match(address, port, strict):
  File "/path/.virtualenvs/simplebwscanner3/lib/python3.5/site-packages/stem-1.6.0.dev0-py3.5.egg/stem/", line 783, in is_match
    comparison_addr_bin &= self._get_mask_bin()
KeyError: (<stem.exit_policy.ExitPolicyRule object at 0x7f3743f70a90>,)
[2018-07-14 14:55:23,007] [sbws.core.scanner] [ERROR] Unhandled exception caught while measuring Unnamed: <class 'KeyError'> (<stem.exit_policy.ExitPolicyRule object at 0x7f3743f70a90>,

comment:7 Changed 2 days ago by juga

Description: modified (diff)
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