gh-143308: fix UAF when PickleBuffer is concurrently mutated in a callback #143312

a12k · 2025-12-31T17:47:36Z

This PR addresses a use-after-free vulnerability in save_picklebuffer in Modules/_pickle.c. The issue occurred when a buffer_callback explicitly released the PickleBuffer while the pickler was still serializing it.

Validation

New Tests: Added test_release_in_callback_keepalive and test_release_in_callback_complex_keepalive to Lib/test/test_pickle.py.

Linked issue: gh-128038

Issue: Use-after-free in save_picklebuffer via re-entrant buffer_callback and __bool__ #143308

Lib/test/test_pickle.py

Misc/NEWS.d/next/Core_and_Builtins/2025-12-31-17-38-33.gh-issue-143308.lY8UCR.rst

Lib/test/pickletester.py

picnixz · 2025-12-31T22:05:13Z

Just a small thing to alter and we're good (good to keep a clickable ref)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Misc/NEWS.d/next/Library/2025-12-31-17-38-33.gh-issue-143308.lY8UCR.rst

Waiting until the NEWS entry has been moved.

…ction

serhiy-storchaka · 2026-01-02T14:37:06Z

Modules/_pickle.c

+
+    int rc = 0;
+    Py_buffer keepalive_view; // to ensure that 'view' is kept alive
+    if (PyObject_GetBuffer(view->obj, &keepalive_view, PyBUF_FULL_RO) != 0) {


Could not we simply apply PyObject_GetBuffer() to the PickleBuffer object itself? We can then get rid of PyPickleBuffer_GetBuffer().

Potentially! I'd want to test it. @picnixz what do you think? Since this hasn't been merged yet now would seem to be the time.

It should work. PyPickleBuffer_GetBuffer just returns a (borrowed) ref so it doesn't get any buffer on it. I think it should work so feel free to check!

This worked great, thanks for the suggestion @serhiy-storchaka. @picnixz The change was a little more involved than expected, but by doing this I was able to remove a redundant view, update all the view-> calls, and the exit: label. All tests pass and confirmed that the patch still holds.

…directly

picnixz · 2026-01-03T18:57:55Z

Modules/_pickle.c

-                                    view->len);
+        if (view.readonly) {
+            rc = _save_bytes_data(st, self, obj, (const char *)view.buf,
+                                    view.len);


Can you vertically align 'view.len' with 'st'? (likewise, some lines below)

picnixz · 2026-01-03T18:58:55Z

Modules/_pickle.c

                        "PickleBuffer can not be pickled when "
                        "pointing to a non-contiguous buffer");


Out of curiosity, but do we have a test for this?

Neither of the tests added test for non-contiguous, but should be straightforward to add a test against a buffer with strides...

I just wanted to be sure that this branch was covered by existing tests or by other tests. We can increase the coverage in a follow-up PR.

serhiy-storchaka

LGTM. 👍

In the following issue we can remove PyPickleBuffer_GetBuffer() and PyPickleBuffer_Release().

miss-islington-app · 2026-01-03T22:02:03Z

Thanks @a12k for the PR, and @picnixz for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14.
🐍🍒⛏🤖

… a callback (pythonGH-143312) (cherry picked from commit 6c53af1) Co-authored-by: Aaron Wieczorek <aaronw@fastmail.com> Co-authored-by: Aaron Wieczorek <woz@Aarons-MacBook-Pro.local> Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

bedevere-app · 2026-01-03T22:02:34Z

GH-143396 is a backport of this pull request to the 3.14 branch.

bedevere-app · 2026-01-03T22:02:38Z

GH-143397 is a backport of this pull request to the 3.13 branch.

…n a callback (GH-143312) (#143396) gh-143308: fix UAF when PickleBuffer is concurrently mutated in a callback (GH-143312) (cherry picked from commit 6c53af1) --------------- Co-authored-by: Aaron Wieczorek <aaronw@fastmail.com> Co-authored-by: Aaron Wieczorek <woz@Aarons-MacBook-Pro.local> Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

…n a callback (GH-143312) (#143397) gh-143308: fix UAF when PickleBuffer is concurrently mutated in a callback (GH-143312) (cherry picked from commit 6c53af1) --------------- Co-authored-by: Aaron Wieczorek <aaronw@fastmail.com> Co-authored-by: Aaron Wieczorek <woz@Aarons-MacBook-Pro.local> Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Fix Use-After-Free in _pickle by incrementing PickleBuffer exports

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Use-after-free in save_picklebuffer via re-entrant buffer_callback and __bool__ #143308

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Remove trailing whitespace in test_pickle.py

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Edit NEWS.d with better description of changes

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Refactor and migrate tests from test_pickle to pickletester

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picnixz changed the title ~~gh-143308: Fix Use-After-Free in _pickle by incrementing PickleBuffer exports~~ gh-143308: fix UAF when PickleBuffer is concurrently mutated in a callback Dec 31, 2025

Aaron Wieczorek added 3 commits December 31, 2025 21:26

Slight refactoring of tests; simplifying some logic

b2117f5

Hardcoding pickle.HIGHEST_PROTOCOL in test

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Hardcoding pickle.HIGHEST_PROTOCOL in test slightly cleaner

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Add clickable issue ref to comment

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Merge branch 'python:main' into fix-picklebuffer-uaf

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Move NEWS entry for issue 143308 from Core_and_Builtins to Library se…

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serhiy-storchaka reviewed Jan 2, 2026

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Refactor save_picklebuffer to use PyObject_GetBuffer on PickleBuffer …

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…directly

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A couple minor line alignments

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picnixz merged commit 6c53af1 into python:main Jan 3, 2026
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		"PickleBuffer can not be pickled when "
		"pointing to a non-contiguous buffer");

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gh-143308: fix UAF when PickleBuffer is concurrently mutated in a callback #143312

gh-143308: fix UAF when PickleBuffer is concurrently mutated in a callback #143312

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