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GH-50162: [C++][Parquet] Avoid int32 overflow in BitPackedRunDecoder::GetBatch offset #50089

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GH-50162: [C++][Parquet] Avoid int32 overflow in BitPackedRunDecoder::GetBatch offset #50089

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750aa76
avoid int32 overflow in BitPackedRunDecoder::GetBatch offset
metsw24-max Jun 4, 2026
480bbb8
assert the run payload bound before computing max_read_bytes
metsw24-max Jun 12, 2026
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12 changes: 8 additions & 4 deletions cpp/src/arrow/util/rle_encoding_internal.h
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Original file line number Diff line number Diff line change
Expand Up @@ -371,15 +371,19 @@ class BitPackedRunDecoder {
/// left.
[[nodiscard]] rle_size_t GetBatch(value_type* out, rle_size_t batch_size,
rle_size_t value_bit_width) {
const int bits_read = values_read_ * value_bit_width;
const int bytes_fully_read = bits_read / 8;
const int64_t bits_read = static_cast<int64_t>(values_read_) * value_bit_width;
const int64_t bytes_fully_read = bits_read / 8;
// The parser only creates runs whose full payload fits in max_read_bytes_ (see
// BitPackedRun), so the max_read_bytes difference below is in [0, max_read_bytes_]
// and fits an int. A negative (unbounded) max_read_bytes_ stays negative.
ARROW_DCHECK(max_read_bytes_ < 0 || bytes_fully_read <= max_read_bytes_);
const uint8_t* unread_data = data_ + bytes_fully_read;

const ::arrow::internal::UnpackOptions opts{
/* .batch_size= */ std::min(batch_size, remaining()),
/* .bit_width= */ value_bit_width,
/* .bit_offset= */ bits_read % 8,
/* .max_read_bytes= */ max_read_bytes_ - bytes_fully_read,
/* .bit_offset= */ static_cast<int>(bits_read % 8),
/* .max_read_bytes= */ static_cast<int>(max_read_bytes_ - bytes_fully_read),
Comment on lines +385 to +386

@AntoinePrv AntoinePrv Jun 11, 2026

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In the same way that it may previously not fit in an int do we know that it will fit it at this point (and not turn negative)?

@metsw24-max metsw24-max Jun 12, 2026

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For parser-produced runs it does hold: PeekImpl only emits a run whose whole payload fits in the remaining buffer (it truncates or rejects the run otherwise), and the BitPackedRun constructor DCHECKs that invariant. Since values_read_ <= values_count_, bytes_fully_read <= max_read_bytes_, so the difference stays in [0, max_read_bytes_], which is itself an rle_size_t. The remaining case is the negative sentinel (no bound), where the difference stays negative and unpack treats any negative value the same as -1. Added a DCHECK at the subtraction site to make that explicit.

};

if constexpr (std::is_same_v<T, bool>) {
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