https://github.com/python/cpython/commit/1e66eae427df71453572d6af4cb765ccaa4ab23e commit: 1e66eae427df71453572d6af4cb765ccaa4ab23e branch: 3.14 author: Miss Islington (bot) <[email protected]> committer: serhiy-storchaka <[email protected]> date: 2026-08-18T12:59:14Z summary:
[3.14] gh-153578: Fix out-of-bounds write in bytearray.extend() with 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 e675e37421357cf0319c5bca2cec533f0909d5b8) Co-authored-by: tonghuaroot (童话) <[email protected]> files: A Misc/NEWS.d/next/Core_and_Builtins/2026-07-11-15-45-00.gh-issue-153578.Qm4Zt9.rst M Lib/test/test_bytes.py M Objects/bytearrayobject.c diff --git a/Lib/test/test_bytes.py b/Lib/test/test_bytes.py index 28d566633eefda1..7fb274ce4270024 100644 --- a/Lib/test/test_bytes.py +++ b/Lib/test/test_bytes.py @@ -1670,6 +1670,30 @@ def test_setslice_trap(self): b[8:] = b self.assertEqual(b, bytearray(list(range(8)) + list(range(256)))) + def test_setslice_reentrant_resize(self): + # gh-153578: a buffer argument whose __buffer__ resizes the bytearray + # while the buffer is being acquired must not leave the slice bounds + # with lo > hi, which drove a negative-size memmove (an out-of-bounds + # write) in the setslice path reached through extend(). + class Evil: + def __init__(self, resize): + self.resize = resize + def __buffer__(self, flags): + self.resize() + return memoryview(b'ABCDEFGH') + # clear() during __buffer__: extend appends to the emptied bytearray. + b = bytearray(b'x' * 100) + b.extend(Evil(b.clear)) + self.assertEqual(b, b'ABCDEFGH') + # partial shrink during __buffer__. + b = bytearray(b'x' * 100) + b.extend(Evil(lambda: b.__delitem__(slice(30, None)))) + self.assertEqual(b, b'x' * 30 + b'ABCDEFGH') + # 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) + def test_iconcat(self): b = bytearray(b"abc") b1 = b diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-07-11-15-45-00.gh-issue-153578.Qm4Zt9.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-07-11-15-45-00.gh-issue-153578.Qm4Zt9.rst new file mode 100644 index 000000000000000..2d5d4058a04ef2c --- /dev/null +++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-07-11-15-45-00.gh-issue-153578.Qm4Zt9.rst @@ -0,0 +1,3 @@ +Fix an out-of-bounds write in :meth:`bytearray.extend` when the bytearray is +resized while the argument's :meth:`~object.__buffer__` is being acquired, for +example by another thread. Patch by tonghuaroot. diff --git a/Objects/bytearrayobject.c b/Objects/bytearrayobject.c index 1209125c70bd8ed..e8d47e50d7f7a82 100644 --- a/Objects/bytearrayobject.c +++ b/Objects/bytearrayobject.c @@ -668,8 +668,11 @@ bytearray_setslice(PyByteArrayObject *self, Py_ssize_t lo, Py_ssize_t hi, bytes = vbytes.buf; } + // gh-153578: __buffer__() may have resized self; re-clamp both bounds. if (lo < 0) lo = 0; + else if (lo > Py_SIZE(self)) + lo = Py_SIZE(self); if (hi < lo) hi = lo; if (hi > Py_SIZE(self)) _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
