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PyObject_GC_Resize doesn't check preheader size #101408

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PyObject_GC_Resize doesn't check preheader size#101408
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3.12only security fixestopic-C-APItype-bugAn unexpected behavior, bug, or error
@colesbury

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@colesbury
colesbury
opened on Jan 29, 2023

The PyObject_GC_Resize implementation in the main branch doesn't check if the object has a preheader:

cpython/Modules/gcmodule.c

Lines 2357 to 2358 in 0ef92d9

PyGC_Head *g = AS_GC(op);
g = (PyGC_Head *)PyObject_Realloc(g, sizeof(PyGC_Head) + basicsize);

The only internal use I see is by _PyTuple_Resize which doesn't have a preheader, but the PyObject_GC_Resize function is publicly documented.

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    3.12only security fixestopic-C-APItype-bugAn unexpected behavior, bug, or error

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