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gh-118561: Fix crash involving list.extend in free-threaded build by colesbury · Pull Request #118723 · python/cpython · GitHub
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gh-118561: Fix crash involving list.extend in free-threaded build #118723

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colesbury merged 2 commits into from
May 9, 2024
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gh-118561: Fix crash involving list.extend in free-threaded build #118723

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gh-118561: Fix crash involving list.extend in free-threaded build
colesbury May 7, 2024
3a5c0c8
Update Misc/NEWS.d/next/Core and Builtins/2024-05-07-16-57-56.gh-issu…
colesbury May 9, 2024
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gh-118561: Fix crash involving list.extend in free-threaded build 
The `list_preallocate_exact` function did not zero initialize array
contents. In the free-threaded build, this could expose uninitialized
memory to concurrent readers between the call to
`list_preallocate_exact` and the filling of the array contents with
items.
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@colesbury
colesbury committed May 7, 2024
commit f45dfa87f52263fe30f8129d6f5c7ea577c60a61
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2024-05-07-16-57-56.gh-issue-118561.wNMKVd.rst
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@@ -0,0 +1,2 @@
Fix race condition in free-threaded build where ``list.extend`` could expose
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uninitialied memory to concurrent readers.
3 changes: 2 additions & 1 deletion Objects/listobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -192,14 +192,15 @@ list_preallocate_exact(PyListObject *self, Py_ssize_t size)
return -1;
}
items = array->ob_item;
memset(items, 0, size * sizeof(PyObject *));
#else
items = PyMem_New(PyObject*, size);
if (items == NULL) {
PyErr_NoMemory();
return -1;
}
#endif
self->ob_item = items;
FT_ATOMIC_STORE_PTR_RELEASE(self->ob_item, items);
self->allocated = size;
return 0;
}
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