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GeezerVison is showing github.com — gh-159739: Keep generic alias arguments alive while formatting errors by jelle-openai · Pull Request #159981 · python/cpython

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@jelle-openai

@jelle-openai jelle-openai commented Oct 20, 2026 •
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Keep generic alias arguments alive while formatting errors. When a generic alias contains a list of parameters and an object claiming to be an unpacked type-variable tuple returns a non-tuple from __typing_subst__, the error path frees the temporary argument tuple before reading it to format a TypeError. That use-after-free can crash the interpreter instead of reporting the invalid substitution.

Backport to 3.15 and 3.14.

  • Issue: Fix minor safety issues #159739

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@jelle-openai
pythongh-159739: Keep generic alias arguments alive while formatting …
1286822 
…errors

Backport to 3.15 and 3.14.
@bedevere-app bedevere-app Bot mentioned this pull request Oct 20, 2026
Fix minor safety issues #159739
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@bedevere-app bedevere-app Bot added the awaiting review label Oct 20, 2026
@JelleZijlstra JelleZijlstra added needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes labels Oct 20, 2026
@JelleZijlstra
JelleZijlstra merged commit 9c649db into python:main Oct 21, 2026
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@miss-islington-app

miss-islington-app Bot commented Oct 21, 2026

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Thanks @jelle-openai for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14, 3.15.
🐍🍒⛏🤖
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@bedevere-app bedevere-app Bot removed the awaiting review label Oct 21, 2026
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bedevere-app Bot commented Oct 21, 2026

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GH-160020 is a backport of this pull request to the 3.15 branch.
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@bedevere-app bedevere-app Bot removed the needs backport to 3.15 bugs and security fixes label Oct 21, 2026
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bedevere-app Bot commented Oct 21, 2026

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GH-160021 is a backport of this pull request to the 3.14 branch.
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@bedevere-app bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label Oct 21, 2026
JelleZijlstra pushed a commit that referenced this pull request Oct 21, 2026
@miss-islington @jelle-openai
[3.15] gh-159739: Keep generic alias arguments alive while formatting…
8411879 
… errors (GH-159981) (#160020)

When a generic alias contains a list of parameters and an object claiming to be an unpacked type-variable tuple returns a non-tuple from `__typing_subst__`, the error path frees the temporary argument tuple before reading it to format a `TypeError`. That use-after-free can crash the interpreter instead of reporting the invalid substitution.
(cherry picked from commit 9c649db)

Co-authored-by: Jelle Zijlstra <[email protected]>
JelleZijlstra pushed a commit that referenced this pull request Oct 21, 2026
@miss-islington @jelle-openai
[3.14] gh-159739: Keep generic alias arguments alive while formatting…
706070c 
… errors (GH-159981) (#160021)

When a generic alias contains a list of parameters and an object claiming to be an unpacked type-variable tuple returns a non-tuple from `__typing_subst__`, the error path frees the temporary argument tuple before reading it to format a `TypeError`. That use-after-free can crash the interpreter instead of reporting the invalid substitution.
(cherry picked from commit 9c649db)

Co-authored-by: Jelle Zijlstra <[email protected]>
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@jelle-openai @JelleZijlstra
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