Fix crash on ellipsis indexing with too many trailing indices - #4396
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Adityaj0 wants to merge 4 commits into
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Fix crash on ellipsis indexing with too many trailing indices#4396Adityaj0 wants to merge 4 commits into
Adityaj0 wants to merge 4 commits into
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mlx_expand_ellipsis in python/src/indexing.cpp computed the ellipsis expansion loop bound as `shape.size() - non_none_indices_after`, mixing an unsigned size_t with a signed int. When an index expression has more non-None indices after the ellipsis than the array has dimensions (e.g. a[..., 0, 0] on a 1-D array), this subtraction underflows to a huge unsigned value, so the loop reads far past the end of the shape vector and pushes an unbounded number of slices, crashing the process (SIGSEGV) instead of raising an error. The existing "too many indices" check in mlx_get_item_nd ran only after this expansion, so it never caught this case. Move the bounds check before expansion and do the arithmetic in signed int, so this now raises the same "Too many indices" ValueError that already applies when the extra indices are before the ellipsis. Adds a regression test in python/tests/test_array.py covering getitem and setitem with an ellipsis followed by too many indices.
nastya236
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August 25, 2026 11:22
nastya236
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Aug 25, 2026
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thanks for the fix! I merged the test into indexing.
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Fixes #4398
Indexing with an ellipsis followed by more non-None indices than the array has dimensions computed an unsigned (size_t) underflow in the ellipsis-expansion loop bound, causing an out-of-bounds read / crash instead of raising a
ValueError. Adds a regression test covering getitem and setitem.