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GH-51222: [C++] Avoid overflow in binary_slice output sizing #52451

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GH-51222: [C++] Avoid overflow in binary_slice output sizing #52451

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5f8ddeb
GH-51222: [C++] Avoid overflow in binary_slice output sizing
Dricmoy Sep 16, 2026
749b542
GH-51222: Address binary slice review feedback
Dricmoy Oct 14, 2026
61c9a9c
GH-51222: Clamp binary slice estimate bounds
Dricmoy Oct 18, 2026
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6 changes: 5 additions & 1 deletion cpp/src/arrow/compute/kernels/scalar_string_ascii.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -2642,7 +2642,11 @@ struct SliceBytesTransform : StringSliceTransformBase {
// on the resulting slice lengths, so return a worst case estimate.
return input_bytes;
}
int64_t max_slice_bytes = (opt.stop - opt.start + opt.step - 1) / opt.step;
// SliceOptions uses INT64_MIN/MAX for open-ended bounds. Clamp both bounds
// before arithmetic so equivalent out-of-range indices cannot overflow the size estimate.
const int64_t start = std::clamp(opt.start, -input_bytes, input_bytes);
const int64_t stop = std::clamp(opt.stop, -input_bytes, input_bytes);
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int64_t max_slice_bytes = (stop - start + opt.step - 1) / opt.step;

@dmitry-chirkov-dremio dmitry-chirkov-dremio Oct 21, 2026

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Check: input "abc", start=1, the default stop, and step=INT64_MAX

The code around here is short, but the arithmetic is fragile. See if you can separate out boundary checks although this might as well be "one last boundary to enforce"...

return std::min(input_bytes, ninputs * std::max<int64_t>(0, max_slice_bytes));
}

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30 changes: 30 additions & 0 deletions cpp/src/arrow/compute/kernels/scalar_string_test.cc
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Expand Up @@ -2702,6 +2702,19 @@ TYPED_TEST(TestBinaryKernels, SliceBytesBasic) {
}

TYPED_TEST(TestBinaryKernels, SliceBytesPosPos) {
constexpr auto max = std::numeric_limits<int64_t>::max();
SliceOptions options_default_stop{/*start=*/1};
const std::string long_input(300, 'x');
this->CheckUnary(
"binary_slice", this->template MakeArray<std::string>({"abcdef", long_input}),
this->template MakeArray<std::string>({"bcdef", std::string(299, 'x')}),
&options_default_stop);
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SliceOptions options_default_stop_step{/*start=*/1, /*stop=*/max, /*step=*/5};
this->CheckUnary("binary_slice",
this->template MakeArray<std::string>({"abcdef", long_input}),
this->template MakeArray<std::string>({"b", std::string(60, 'x')}),
&options_default_stop_step);

SliceOptions options{2, 4};
this->CheckUnary(
"binary_slice",
Expand Down Expand Up @@ -2748,6 +2761,23 @@ TYPED_TEST(TestBinaryKernels, SliceBytesPosNeg) {
}

TYPED_TEST(TestBinaryKernels, SliceBytesNegNeg) {
constexpr auto min = std::numeric_limits<int64_t>::min();
const std::string long_input(300, 'x');
SliceOptions options_extreme_start{/*start=*/min, /*stop=*/-1};
this->CheckUnary("binary_slice", this->template MakeArray<std::string>({"x"}),
this->template MakeArray<std::string>({""}),
&options_extreme_start);

SliceOptions options_min{/*start=*/-1, /*stop=*/min};
this->CheckUnary("binary_slice",
this->template MakeArray<std::string>({"abcdef", long_input}),
this->template MakeArray<std::string>({"", ""}), &options_min);
SliceOptions options_min_step_neg{/*start=*/-1, /*stop=*/min, /*step=*/-5};
this->CheckUnary("binary_slice",
this->template MakeArray<std::string>({"abcdef", long_input}),
this->template MakeArray<std::string>({"fa", std::string(60, 'x')}),
&options_min_step_neg);

SliceOptions options{-2, -1};
this->CheckUnary(
"binary_slice",
Expand Down
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