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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
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5 changes: 4 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 +2642,10 @@ 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 stop before
// arithmetic so equivalent out-of-range indices cannot overflow the size estimate.
const int64_t stop = std::clamp(opt.stop, -input_bytes, input_bytes);

@pitrou pitrou Oct 13, 2026

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Can you add a comment explaining the motivation for this?

int64_t max_slice_bytes = (stop - opt.start + opt.step - 1) / opt.step;
return std::min(input_bytes, ninputs * std::max<int64_t>(0, max_slice_bytes));
}

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25 changes: 25 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);

@pitrou pitrou Oct 13, 2026

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I think we can add a couple other interesting cases:

  • start=1, step=5
  • start=-1, stop=INT64_MIN
  • start=-1, stop=INT64_MIN, step=-5

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 +2761,18 @@ 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_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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