Memory leak in Modules/main.c:pymain_parse_cmdline_impl when using the CLI flag

[Lucas-C]

BPO	35720
Nosy	@vstinner, @miss-islington, @Lucas-C
PRs	bpo-35720: Fixing a memory leak in Modules/main.c:pymain_parse_cmdline_impl #11528 bpo-35720: Fixing a memory leak in Modules/main.c:pymain_parse_cmdline_impl #11528 bpo-35720: Fixing a memory leak in Modules/main.c:pymain_parse_cmdline_impl #11528 [3.7] bpo-35720: Fixing a memory leak in pymain_parse_cmdline_impl() (GH-11528) #11648 [3.7] bpo-35720: Fixing a memory leak in pymain_parse_cmdline_impl() (GH-11528) #11648

^{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 2019-01-22.16:43:52.001>
created_at = <Date 2019-01-11.19:14:02.668>
labels = ['3.7', '3.8', 'performance']
title = 'Memory leak in Modules/main.c:pymain_parse_cmdline_impl when using the CLI flag'
updated_at = <Date 2019-01-22.16:43:52.000>
user = 'https://github.com/Lucas-C'

bugs.python.org fields:

activity = <Date 2019-01-22.16:43:52.000>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-01-22.16:43:52.001>
closer = 'vstinner'
components = []
creation = <Date 2019-01-11.19:14:02.668>
creator = 'Lucas Cimon'
dependencies = []
files = []
hgrepos = []
issue_num = 35720
keywords = ['patch', 'patch', 'patch']
message_count = 4.0
messages = ['333499', '334217', '334220', '334221']
nosy_count = 3.0
nosy_names = ['vstinner', 'miss-islington', 'Lucas Cimon']
pr_nums = ['11528', '11528', '11528', '11648', '11648']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'resource usage'
url = 'https://bugs.python.org/issue35720'
versions = ['Python 3.7', 'Python 3.8']

[Lucas-C]

Hi.

I think I have found a minor memory leak in Modules/main.c:pymain_parse_cmdline_impl.

When the loop in the pymain_read_conf function in this same file
calls pymain_init_cmdline_argv a 2nd time, the pymain->command
buffer of wchar_t is overriden and the previously allocated memory
is never freed.

I haven't written any code test to reproduce this,
but it can be tested easily with gdb:

gdb -- bin/python3 -c pass
start
b Modules/main.c:587
b pymain_clear_pymain
c
c

You'll see that PyMem_RawMalloc is called twice without pymain->command ever being freed in pymain_clear_pymain.

I have a patch coming as PR on GitHub

I'd be glad to have your feedback on this issue and my proposal for a fix.

Regards.

[vstinner]

New changeset 35ca182 by Victor Stinner (Lucas Cimon) in branch 'master':
bpo-35720: Fixing a memory leak in pymain_parse_cmdline_impl() (GH-11528)
35ca182

[miss-islington]

New changeset f71e743 by Miss Islington (bot) in branch '3.7':
bpo-35720: Fixing a memory leak in pymain_parse_cmdline_impl() (GH-11528)
f71e743

[vstinner]

Thanks Lucas Cimon!