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GeezerVison is showing github.com — gh-78724: raise RuntimeError's when calling methods on non-ready Struct()'s by skirpichev · Pull Request #143643 · python/cpython

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skirpichev commented Jan 10, 2026 •

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Issue: _struct.Struct: calling functions without calling __init__ results in SystemError #78724

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skirpichev added 5 commits

January 3, 2026 10:36


          pythongh-143379: fix UAF in struct.Struct.pack() when object modified…

a1c2603

… by dunder methods


          Merge branch 'master' into fix-uaf-s_pack_internal/143379

716e28c


          address review: implement a different solution with a mutex flag

e611953

Now modification of the Struct() while packing trigger a RuntimeError


          + clean the mess

ab62167


          pythongh-78724: raise RuntimeError's when calling methods on non-read…

3b18427

…y Struct()'s

Calling the ``Struct.__new__()`` dunder without required argument now is
deprecated.  Calling the ``Struct.__init__()`` dunder method on
initialized object now also is deprecated.

bedevere-app Bot mentioned this pull request

Jan 10, 2026

_struct.Struct: calling functions without calling __init__ results in SystemError #78724

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skirpichev mentioned this pull request

Jan 10, 2026

gh-143379: fix UAF in struct.Struct.pack() when object modified by dunder methods #143382

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skirpichev marked this pull request as ready for review

January 10, 2026 07:55

bedevere-app Bot added the awaiting review label

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skirpichev requested a review from serhiy-storchaka

January 10, 2026 07:56

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Jan 10, 2026

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This issue is relatively independed from the concurrent packing issue, so I suggest fir it separately. We should not add deprecation in maintained versions, so I suggest to only leave checks that Struct was initialized, and add the deprecation in a separate PR.

prepare_s() should be rewritten so it only sets s_codes and other fields when it is successful.

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Modules/_struct.c Resolved

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Modules/_struct.c Outdated

		{
		PyObject *self;

		if (PyTuple_GET_SIZE(args) != 1

serhiy-storchaka Jan 10, 2026

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I do not see how can this be useful.

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skirpichev Jan 10, 2026

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This is to trigger deprecation warning in a following scenario:

>>> import struct
>>> class MyStruct(struct.Struct):
...     def __init__(self):
...         super().__init__('>h')
...         
>>> my_struct = MyStruct()
<python-input-2>:1: DeprecationWarning: Struct().__new__() has one required argument

PS: deprecation part moved to #143659.

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serhiy-storchaka added needs backport to 3.13

only security fixes

needs backport to 3.14 bugs and security fixes labels

Jan 10, 2026

skirpichev marked this pull request as draft

January 10, 2026 10:14

bedevere-app Bot removed the awaiting review label

Jan 10, 2026

skirpichev added 3 commits

January 10, 2026 13:15


          Merge branch 'master' into deprecate-struct-init/78724

54dbea8


          revert stuff from python#143382

b6c8bed


          revert deprecations (TBD: a separate pr)

f542173

skirpichev commented Jan 10, 2026

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prepare_s() should be rewritten so it only sets s_codes and other fields when it is successful.

I think it's already the case. We can move a bit s_size/s_len assignments, but as far as we interested only in s_codes - I'm not sure if it's worth. There should be no failures after codes = PyMem_Malloc(...).

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          address review: redo patch to use s_codes

69a5eec

skirpichev marked this pull request as ready for review

January 10, 2026 11:45

bedevere-app Bot added the awaiting review label

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skirpichev requested a review from serhiy-storchaka

January 10, 2026 11:46


          Merge branch 'main' into deprecate-struct-init/78724

0e6af95

serhiy-storchaka commented Jan 10, 2026

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Well, it does not matter. It would reduce the chance of race condition, but nobody should run __init__() and pack() concurrently, there are no reasons to do this, and we should not support this.

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serhiy-storchaka reviewed

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          address review: -asserts + redo test

8ba6b33

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Lib/test/test_struct.py Outdated

		self.assertRaises(RuntimeError, meth, spam)
		self.assertRaises(RuntimeError, S.iter_unpack, 1)
		self.assertRaises(RuntimeError, S.pack, 1)
		self.assertRaises(RuntimeError, S.pack_into, 1)

serhiy-storchaka Jan 10, 2026

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S.pack_into(buffer, offset, v1, v2, ...)

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skirpichev Jan 10, 2026

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BTW, I think that argument processing in the struct's functions/methods should be refactored and transformed to the AC. E.g. S.pack_info could check required arguments before validation of the soself struct.

Though, this belongs to a separate issue.

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skirpichev Jan 11, 2026

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AC cleanup goes to #143673

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          address review: adjust tests

ea0f8e2

skirpichev commented Jan 10, 2026

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Well, it does not matter. It would reduce the chance of race condition, but nobody should run __init__() and pack() concurrently, there are no reasons to do this, and we should not support this.

I guess this belongs to the #143382 pr thread.

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skirpichev requested a review from serhiy-storchaka

January 11, 2026 11:09

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skirpichev added 2 commits

January 11, 2026 18:21


          Merge branch 'master' into deprecate-struct-init/78724

c71be45


          address review: revert unrelated change

b61bddb

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LGTM. 👍

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bedevere-app Bot added awaiting merge and removed awaiting review labels

Jan 11, 2026

serhiy-storchaka enabled auto-merge (squash)

January 11, 2026 15:47

serhiy-storchaka merged commit 515ae40 into python:main

Jan 11, 2026

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miss-islington-app Bot commented Jan 11, 2026

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Thanks @skirpichev for the PR, and @serhiy-storchaka for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14.
🐍🍒⛏🤖

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miss-islington pushed a commit to miss-islington/cpython that referenced this pull request

Jan 11, 2026


          pythongh-78724: Raise RuntimeError's when calling methods on non-read…

660b508

…y Struct()'s (pythonGH-143643)

(cherry picked from commit 515ae40)

Co-authored-by: Sergey B Kirpichev <[email protected]>

miss-islington-app Bot commented Jan 11, 2026

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Sorry, @skirpichev and @serhiy-storchaka, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 515ae4078dffa0b74e5e5431462c2f4fe4563ffa 3.13

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miss-islington-app Bot assigned serhiy-storchaka

Jan 11, 2026

bedevere-app Bot commented Jan 11, 2026

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GH-143695 is a backport of this pull request to the 3.14 branch.

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bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label

Jan 11, 2026

skirpichev deleted the deprecate-struct-init/78724 branch

January 11, 2026 18:04

skirpichev self-assigned this

Jan 11, 2026

bedevere-app Bot commented Jan 11, 2026

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GH-143714 is a backport of this pull request to the 3.13 branch.

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bedevere-app Bot removed the needs backport to 3.13 only security fixes label

Jan 11, 2026

skirpichev removed their assignment

Jan 11, 2026

serhiy-storchaka pushed a commit that referenced this pull request

Jan 12, 2026


          [3.14] gh-78724: Raise RuntimeError's when calling methods on non-rea…

8f85adc

…dy Struct()'s (GH-143643) (GH-143695)

(cherry picked from commit 515ae40)

Co-authored-by: Sergey B Kirpichev <[email protected]>

serhiy-storchaka pushed a commit that referenced this pull request

Jan 12, 2026


          [3.13] gh-78724: Raise RuntimeError's when calling methods on non-rea…

8fd4435

…dy Struct()'s (GH-143643) (GH-143714)

(cherry picked from commit 515ae40)

reidenong pushed a commit to reidenong/cpython that referenced this pull request

Jan 12, 2026


          pythongh-78724: Raise RuntimeError's when calling methods on non-read…

e3ef2fc

…y Struct()'s (pythonGH-143643)

thunder-coding pushed a commit to thunder-coding/cpython that referenced this pull request

Feb 15, 2026


          pythongh-78724: Raise RuntimeError's when calling methods on non-read…

3ab851b

…y Struct()'s (pythonGH-143643)

serhiy-storchaka removed their assignment

Jul 15, 2026

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skirpichev commented Jan 10, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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skirpichev commented Jan 10, 2026 •

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