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gh-115874: Don't use module state in teedataobject tp_dealloc #116204

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Merged
merged 3 commits into from
Mar 18, 2024
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gh-115874: Don't use module state in teedataobject tp_dealloc #116204

merged 3 commits into from
Mar 18, 2024

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erlend-aasland
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@erlend-aasland erlend-aasland commented Mar 1, 2024 •
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@bedevere-app bedevere-app bot mentioned this pull request Mar 1, 2024
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@erlend-aasland erlend-aasland added the needs backport to 3.12 only security fixes label Mar 1, 2024
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We could also add your repro as a regression test, @brandtbucher.

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I think adding the test is a good idea. Maybe use one of the helpers that launches a new subprocess?

Honestly, I’m not sure why the safe dealloc function needs a type at all. It’s not possible to have any other type here, right? In fact, it’s basically just reinventing the existing trashcan mechanism.

Either one of two things is true: the type of a linked object can never be anything other than teedataobject_type, and the check is unnecessary (it’s not subclass-able, and the code goes to great lengths to make sure that other classes aren’t used here). Or it is possible to have another type of object here and the current code is incorrect (and we should just use the Py_TRASHCAN macros in the dealloc function).

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erlend-aasland commented Mar 1, 2024 •
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Honestly, I’m not sure why the safe dealloc function needs a type at all. It’s not possible to have any other type here, right?

Well, it's not a basetype, so there is no risk of subtypes here. After a second (quick) look, I see no reason to use the module state here at all. I'll be able to have a closer look in a couple of hours. Feel free to continue working on this PR in the mean time if you want, Brandt.

We could just decref the linked list in the dealloc function; the teedataobject_safe_decref abstraction is not needed, and it is not really helping either IMO.

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FTR, here's the issue and commit that added the safe-decref helper:

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Using the Py_TRASHCAN macros should also be fine AFAIK, but I've never had to deal with them before so I'm on thin ice there :)

serhiy-storchaka
serhiy-storchaka approved these changes Mar 2, 2024
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It is not obvious why the typing module is needed for tests. It may make the test unreliable. Otherwise LGTM.

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It is not obvious why the typing module is needed for tests. It may make the test unreliable. Otherwise LGTM.

It is not obvious for me either. @brandtbucher, could you add an explanatory comment?

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brandtbucher commented Mar 2, 2024 •
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Away from my laptop for the weekend, but I’ll look when I get back.

Honestly, I think it may just have to do with the order in which cycles are created (and the order in which they, and the items within them, are cleared). typing creates a few cycles between itself and copyreg on import. @JelleZijlstra noted on the original issue that the bug goes away if those cycles aren’t created, even though the cycles themselves aren’t part of the problem.

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Perhaps the GitHub reference is enough for now.

erlend-aasland
erlend-aasland commented Mar 12, 2024
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Lib/test/test_itertools.py
@@ -1699,6 +1699,14 @@ def test_tee(self):
self.pickletest(proto, a, compare=ans)
self.pickletest(proto, b, compare=ans)

def test_tee_dealloc_segfault(self):
# gh-115874: segfaults when accessing module state in tp_dealloc.
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@erlend-aasland erlend-aasland Mar 12, 2024 •
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@brandtbucher, how about this:

Suggested change
# gh-115874: segfaults when accessing module state in tp_dealloc.
# gh-115874: Segfault when accessing module state in tp_dealloc.
# The repro depends on multiple ref cycles; by importing
# typing, we implicitly create ref cycles between typing
# and copyreg. Without these cycles, the reproducer does
# not work.

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Perhaps the GitHub reference is enough for now.

No-one chimed in, so we assume it is. If someone feels the urge to clarify the comment further, a follow-up PR can be made.

@erlend-aasland erlend-aasland merged commit e2fcaf1 into python:main Mar 18, 2024
@erlend-aasland erlend-aasland deleted the fix-tp-dealloc-in-teedataobject branch March 18, 2024 12:24
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Thanks @erlend-aasland for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Mar 18, 2024
@erlend-aasland @brandtbucher @miss-islington
pythongh-115874: Don't use module state in teedataobject tp_dealloc (p…
fb64bb0 
…ythonGH-116204)

(cherry picked from commit e2fcaf1)

Co-authored-by: Erlend E. Aasland <[email protected]>
Co-authored-by: Brandt Bucher <[email protected]>
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bedevere-app bot commented Mar 18, 2024

GH-116955 is a backport of this pull request to the 3.12 branch.

@bedevere-app bedevere-app bot removed the needs backport to 3.12 only security fixes label Mar 18, 2024
erlend-aasland added a commit that referenced this pull request Mar 18, 2024
@miss-islington @erlend-aasland @brandtbucher
[3.12] gh-115874: Don't use module state in teedataobject tp_dealloc (G…
1c0c6c9 
…H-116204) (#116955)

(cherry picked from commit e2fcaf1)

Co-authored-by: Erlend E. Aasland <[email protected]>
Co-authored-by: Brandt Bucher <[email protected]>
@erlend-aasland erlend-aasland mentioned this pull request Mar 19, 2024
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vstinner pushed a commit to vstinner/cpython that referenced this pull request Mar 20, 2024
@erlend-aasland @brandtbucher @vstinner
pythongh-115874: Don't use module state in teedataobject tp_dealloc (p…
194671b 
…ython#116204)

Co-authored-by: Brandt Bucher <[email protected]>
adorilson pushed a commit to adorilson/cpython that referenced this pull request Mar 25, 2024
@erlend-aasland @brandtbucher @adorilson
pythongh-115874: Don't use module state in teedataobject tp_dealloc (p…
fa75cdd 
…ython#116204)

Co-authored-by: Brandt Bucher <[email protected]>
diegorusso pushed a commit to diegorusso/cpython that referenced this pull request Apr 17, 2024
@erlend-aasland @brandtbucher @diegorusso
pythongh-115874: Don't use module state in teedataobject tp_dealloc (p…
231a673 
…ython#116204)

Co-authored-by: Brandt Bucher <[email protected]>
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@serhiy-storchaka serhiy-storchaka serhiy-storchaka approved these changes

@rhettinger rhettinger Awaiting requested review from rhettinger rhettinger is a code owner

@brandtbucher brandtbucher Awaiting requested review from brandtbucher

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