ipaddres.IPv4Network and ipaddress.IPv6Network tuple construction will accept out of valid range prefixlen

[niconorsk]

BPO	36845
Nosy	@methane, @serhiy-storchaka, @niconorsk
PRs	bpo-36845: validate integer network prefix when constructing IP networks #13298 [3.7] bpo-36845: validate integer network prefix when constructing IP networks (GH-13298) #13309

^{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 2019-05-14.11:00:45.278>
created_at = <Date 2019-05-07.22:53:58.767>
labels = ['3.7', '3.8', 'type-bug', 'library']
title = 'ipaddres.IPv4Network and ipaddress.IPv6Network tuple construction will accept out of valid range prefixlen'
updated_at = <Date 2019-05-14.11:00:45.278>
user = 'https://github.com/niconorsk'

bugs.python.org fields:

activity = <Date 2019-05-14.11:00:45.278>
actor = 'methane'
assignee = 'none'
closed = True
closed_date = <Date 2019-05-14.11:00:45.278>
closer = 'methane'
components = ['Library (Lib)']
creation = <Date 2019-05-07.22:53:58.767>
creator = 'niconorsk'
dependencies = []
files = []
hgrepos = []
issue_num = 36845
keywords = ['patch']
message_count = 6.0
messages = ['341839', '341861', '341862', '341863', '342448', '342449']
nosy_count = 5.0
nosy_names = ['pmoody', 'methane', 'SilentGhost', 'serhiy.storchaka', 'niconorsk']
pr_nums = ['13298', '13309']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue36845'
versions = ['Python 3.7', 'Python 3.8']

[niconorsk]

When using the tuple-form of constructing IPv4Network and IPv6Network will accept prefixlen outside of the normal allowed ranges.

Example:
>>> import ipaddress
>>> ipaddress.IPv4Network(('172.21.1.0', 400))
IPv4Network('172.21.1.0/400')

If given a negative number, it will error but not with a particularly useful error:
>>> x = ipaddress.IPv4Network(('172.21.1.0', -1))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python3.7/ipaddress.py", line 1532, in __init__
    self.netmask, self._prefixlen = self._make_netmask(mask)
  File "/usr/lib64/python3.7/ipaddress.py", line 1112, in _make_netmask
    netmask = IPv4Address(cls._ip_int_from_prefix(prefixlen))
  File "/usr/lib64/python3.7/ipaddress.py", line 444, in _ip_int_from_prefix
    return cls._ALL_ONES ^ (cls._ALL_ONES >> prefixlen)
ValueError: negative shift count

Looking at the code, I think all that is needed is a range check within the respective _make_netmask methods in _BaseV4 and _BaseV6 classes

[SilentGhost]

Would you like to submit a fix, Nicolai?

[niconorsk]

I'd be happy too. Would be a first time contribution though, so need to give me some time to figure my way around the process.

[SilentGhost]

There are some guidelines available at https://devguide.python.org/pullrequest/

[methane]

New changeset 5e48e3d by Inada Naoki (Nicolai Moore) in branch 'master':
bpo-36845: validate integer network prefix when constructing IP networks (GH-13298)
5e48e3d

[methane]

New changeset 30cccf0 by Inada Naoki (Miss Islington (bot)) in branch '3.7':
bpo-36845: validate integer network prefix when constructing IP networks (GH-13298)
30cccf0