gh-153578: Fix out-of-bounds write in bytearray.extend() with a reentrant __buffer__ - #153579
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serhiy-storchaka merged 2 commits intoAug 18, 2026
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… reentrant __buffer__ bytearray.extend() clamped only the high bound of the append range to the current size after acquiring the argument's buffer, so a __buffer__ that shrinks the bytearray left the low bound past the high bound and ran a negative-size memmove. Clamp the low bound too, matching bytearray.__iadd__.
serhiy-storchaka
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needs backport to 3.13
serhiy-storchaka
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Aug 17, 2026
| b = bytearray(b'x' * 100) | ||
| b.extend(Evil(lambda: b.__delitem__(slice(30, None)))) | ||
| self.assertEqual(b, b'x' * 30 + b'ABCDEFGH') | ||
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Add the third case:
# grow during __buffer__: the data lands at the original end.
b = bytearray(b'x' * 10)
b.extend(Evil(lambda: b.extend(b'y' * 100)))
self.assertEqual(b, b'x' * 10 + b'ABCDEFGH' + b'y' * 100)
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The defect isn't "reentrancy from a deliberately evil |
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Done in 5128c85: reframed the NEWS as a concurrency (any GIL-releasing |
serhiy-storchaka
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Aug 18, 2026
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Thanks @tonghuaroot for the PR, and @serhiy-storchaka for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14, 3.15. |
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GH-156007 is a backport of this pull request to the 3.15 branch. |
bedevere-app
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needs backport to 3.15
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GH-156008 is a backport of this pull request to the 3.14 branch. |
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GH-156009 is a backport of this pull request to the 3.13 branch. |
serhiy-storchaka
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Aug 18, 2026
…a reentrant __buffer__ (GH-153579) (GH-156008) bytearray.extend() clamped only the high bound of the append range to the current size after acquiring the argument's buffer, so a __buffer__ that shrinks the bytearray left the low bound past the high bound and ran a negative-size memmove. Clamp the low bound too, matching bytearray.__iadd__. (cherry picked from commit e675e37) Co-authored-by: tonghuaroot (童话) <tonghuaroot@gmail.com>
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bytearray.extend()clamped only the high bound of the append range to the current size after acquiring theargument's buffer, so a
__buffer__that shrinks the bytearray left the low bound past the high bound and rana negative-size
memmove. Clamp the low bound too, matchingbytearray.__iadd__.