base64.b32decode() leads into UnboundLocalError and OverflowError on some data

[Barro]

BPO	34164
Nosy	@serhiy-storchaka, @Barro
PRs	bpo-34164: Fix handling of incorrect padding in base64.b32decode(). #8351 [3.7] bpo-34164: Fix handling of incorrect padding in base64.b32decode(). (GH-8351) #8435 [3.6] bpo-34164: Fix handling of incorrect padding in base64.b32decode(). (GH-8351) #8436

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2018-07-24.12:12:19.397>
created_at = <Date 2018-07-20.09:21:09.721>
labels = ['3.7', '3.8', 'type-bug', 'library']
title = 'base64.b32decode() leads into UnboundLocalError and OverflowError on some data'
updated_at = <Date 2018-07-24.12:12:19.396>
user = 'https://github.com/Barro'

bugs.python.org fields:

activity = <Date 2018-07-24.12:12:19.396>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2018-07-24.12:12:19.397>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2018-07-20.09:21:09.721>
creator = 'Barro'
dependencies = []
files = []
hgrepos = []
issue_num = 34164
keywords = ['patch']
message_count = 6.0
messages = ['321991', '321992', '322012', '322284', '322289', '322294']
nosy_count = 2.0
nosy_names = ['serhiy.storchaka', 'Barro']
pr_nums = ['8351', '8435', '8436']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue34164'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

[Barro]

base64.b32decode() function leads into "UnboundLocalError: local variable 'acc' referenced before assignment" when passing 8 equality signs as data:

>>> import base64
>>> base64.b32decode(b"========")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/tmp/python-3.7-bin/lib/python3.7/base64.py", line 235, in b32decode
    acc <<= 5 * padchars
UnboundLocalError: local variable 'acc' referenced before assignment

When passing a different number of equality signs, the documented binascii.Error exception is thrown.

[Barro]

Apparently base64.b32decode() also has another issue that I missed when going through the issues with base64 module:

>>> import base64
>>> base64.b32decode(b"M===============================")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/tmp/python-3.7-bin/lib/python3.7/base64.py", line 236, in b32decode
    last = acc.to_bytes(5, 'big')
OverflowError: int too big to convert

[serhiy-storchaka]

Thank you for your report Jussi.

The type "crash" is used for hard crashes of the Python interpreter – possibly with a core dump or a Windows error box.

[serhiy-storchaka]

New changeset ac0b3c2 by Serhiy Storchaka in branch 'master':
bpo-34164: Fix handling of incorrect padding in base64.b32decode(). (GH-8351)
ac0b3c2

[serhiy-storchaka]

New changeset 0b27169 by Serhiy Storchaka (Miss Islington (bot)) in branch '3.7':
bpo-34164: Fix handling of incorrect padding in base64.b32decode(). (GH-8351) (GH-8435)
0b27169

[serhiy-storchaka]

New changeset 113f86e by Serhiy Storchaka in branch '3.6':
[3.6] bpo-34164: Fix handling of incorrect padding in base64.b32decode(). (GH-8351) (GH-8436)
113f86e