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bpo-39068 guard _b85chars2 initialization #17627

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drmonkeysee wants to merge 2 commits into python:master from drmonkeysee:base85-race-condition-fix

+2 −2

drmonkeysee commented Dec 16, 2019 •

edited by bedevere-bot

Under multi-threading scenarios a race condition may occur where a thread sees an initialized _b85chars table but an uninitialized _b85chars2 table due to the guard only checking the first table.

This causes an exception like:

  File "/usr/lib/python3.6/base64.py", line 434, in b85encode
    return _85encode(b, _b85chars, _b85chars2, pad),
  File "/usr/lib/python3.6/base64.py", line 294, in _85encode
    for word in words],
  File "/usr/lib/python3.6/base64.py", line 294, in <listcomp>
    for word in words],
 "TypeError: 'NoneType' object is not subscriptable

https://bugs.python.org/issue39068


        guard _b85chars2 table

04967d1

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the-knights-who-say-ni commented Dec 16, 2019

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bedevere-bot added the awaiting review label

Commod0re approved these changes

bedevere-bot added awaiting core review and removed awaiting review labels

camhawkins approved these changes

drmonkeysee changed the title ~~guard _b85chars2 table~~ bpo-39068 guard _b85chars2 table

drmonkeysee changed the title ~~bpo-39068 guard _b85chars2 table~~ bpo-39068 guard _b85chars2 initialization

IEarle approved these changes

serhiy-storchaka reviewed

Lib/base64.py Outdated

  
      @@ -430,6 +430,7 @@ def b85encode(b, pad=False):
    
            # if the function is never called

            if _b85chars is None:

serhiy-storchaka Dec 16, 2019

Member

It is enough to check if _b85chars2 is None here.

These checks are cheap, but they are performed at every b85encode() call. Lesser checks is better.

a85encode() should be updated too. And may be other functions if they initialize two or more globals.

drmonkeysee Dec 16, 2019 •

edited

Author

done. visually scanned the file for other cases but only found the additional one in a85encode().


        only check latter var and fix a85 as well

bf5a325

the-knights-who-say-ni added CLA signed and removed CLA not signed labels

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