Segfault in command line processing due to buffer over-read

[cgohlke]

BPO	33706
Nosy	@vstinner, @miss-islington
PRs	bpo-33706: Fix pymain_parse_cmdline_impl() #7283 [3.7] bpo-33706: Fix pymain_parse_cmdline_impl() (GH-7283) #7284
Files	master...cgohlke patch-1.diff

^{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 2018-05-31.14:14:27.497>
created_at = <Date 2018-05-31.06:31:10.545>
labels = ['interpreter-core', '3.7', '3.8', 'type-crash']
title = 'Segfault in command line processing due to buffer over-read'
updated_at = <Date 2018-05-31.14:14:27.495>
user = 'https://bugs.python.org/cgohlke'

bugs.python.org fields:

activity = <Date 2018-05-31.14:14:27.495>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2018-05-31.14:14:27.497>
closer = 'vstinner'
components = ['Interpreter Core']
creation = <Date 2018-05-31.06:31:10.545>
creator = 'cgohlke'
dependencies = []
files = ['47628']
hgrepos = []
issue_num = 33706
keywords = ['patch']
message_count = 4.0
messages = ['318260', '318302', '318310', '318315']
nosy_count = 3.0
nosy_names = ['vstinner', 'cgohlke', 'miss-islington']
pr_nums = ['7283', '7284']
priority = 'critical'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue33706'
versions = ['Python 3.7', 'Python 3.8']

[cgohlke]

When testing Python 3.7.0b5 x64 (and betas before) on Windows 10, I occasionally get segfaults when passing a program as string on the command line. The shortest command to reproduce this on my system is python.exe -c 1 with heap detection turned on but that might not be reproducible on other systems.

It turns out there is a buffer over-read when copying the PyOS_optarg string in main.c. The attached patch fixes the segfault on my system.

[vstinner]

New changeset 58d1683 by Victor Stinner in branch 'master':
bpo-33706: Fix pymain_parse_cmdline_impl() (GH-7283)
58d1683

[miss-islington]

New changeset c6de46e by Miss Islington (bot) in branch '3.7':
bpo-33706: Fix pymain_parse_cmdline_impl() (GH-7283)
c6de46e

[vstinner]

Thank you Christoph Gohlke for your bug report and your fix! I fixed 3.7 and master branches.