Clear audit hooks after destructors

[zooba]

BPO	41162
Nosy	@tiran, @zooba, @zkonge, @frankli0324
PRs	bpo-41162: Clear audit hooks after destructors #21222 [3.9] bpo-41162: Clear audit hooks later during finalization (GH-21222) #21302 [3.8] bpo-41162: Clear audit hooks later during finalization (GH-21222) #21303 [3.9] bpo-41162: Fix improperly merged change so that final hooks are called before types are cleared #21304
Files	clearaudithook.patch

^{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 = None
created_at = <Date 2020-06-29.16:28:11.224>
labels = ['type-security', 'interpreter-core', '3.8', '3.9', '3.10']
title = 'Clear audit hooks after destructors'
updated_at = <Date 2020-07-06.19:23:17.309>
user = 'https://github.com/zooba'

bugs.python.org fields:

activity = <Date 2020-07-06.19:23:17.309>
actor = 'steve.dower'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2020-06-29.16:28:11.224>
creator = 'steve.dower'
dependencies = []
files = ['49276']
hgrepos = []
issue_num = 41162
keywords = ['patch']
message_count = 7.0
messages = ['372601', '372610', '372892', '372958', '372965', '372970', '373158']
nosy_count = 4.0
nosy_names = ['christian.heimes', 'steve.dower', 'zkonge', 'frankli']
pr_nums = ['21222', '21302', '21303', '21304']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'security'
url = 'https://bugs.python.org/issue41162'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

[zooba]

Because of when _Py_ClearAuditHooks is called during finalization, it is possible that __del__ destructors will be called after hooks have been cleared. Audit events that would be raised here are dropped.

We should ensure these events are received by any known hooks for the interpreter (Python) or the runtime (C).

(Thanks to Frank Li for the report.)

[zkonge]

Patch attached below works well, but with less functionality for users' audit hook.
Pure Python audit hook implement looks safe enough.
Should we need call _PySys_ClearAuditHooks earlier for more functionality?

[zooba]

PR 21222 (with test updates) is a good fix, though we know there can still be arbitrary code executed afterwards. But it's not in a place where we can reliably hook.

Probably the best thing to do is to make sure that events are raised for anything that would be required to add code there. Though that may not be feasible either, but since nobody should be doing that kind of thing deliberately, detection is just as valuable as prevention.

[zooba]

New changeset daa0fe0 by Konge in branch 'master':
bpo-41162: Clear audit hooks later during finalization (GH-21222)
daa0fe0

[zooba]

New changeset e1d4fdc by Steve Dower in branch '3.9':
bpo-41162: Clear audit hooks later during finalization (GH-21222)
e1d4fdc

[zooba]

New changeset b9e288c by Steve Dower in branch '3.8':
bpo-41162: Clear audit hooks later during finalization (GH-21222)
b9e288c

[zooba]

Merged the initial fix, but we now need to find any exploitable paths that remain.

Considering how late in finalization they now run, they're very unlikely to succeed at doing anything interesting. However, they'd also qualify as bugs (potentially crashes), so we'll want to find ways to make them run earlier anyway.