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The points[] and scalars[] typemaps read a memoryview argument through
PyMemoryView_GET_BUFFER() without acquiring it. A released memoryview
keeps its stale Py_buffer, so once mv.release() drops the last reference
to the underlying bytes object the typemap dereferences freed memory. A
negatively strided view such as memoryview(b)[::-1] points buf at the
last byte while len is the full length, so blst_p{1,2}s_mult_pippenger
reads up to len-1 bytes past the end of the object.
Acquire the buffer with PyObject_GetBuffer(PyBUF_SIMPLE), which rejects
released and non-contiguous views, and hold it until freearg.
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acquire the memoryview buffer with PyObject_GetBuffer(PyBUF_SIMPLE) in the points[] and scalars[] typemaps behind P{1,2}_Affines.mult_pippenger, otherwise a released view (heap-use-after-free under ASan) or a negatively strided one like memoryview(b)[::-1] (heap-buffer-overflow, len-1 bytes past the object) reaches blst_p{1,2}s_mult_pippenger;