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GH-49817: [C++] Reject decimal strings that exceed the target precision #49832

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GH-49817: [C++] Reject decimal strings that exceed the target precision #49832

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18 changes: 18 additions & 0 deletions cpp/src/arrow/util/decimal.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -879,6 +879,16 @@ Status DecimalFromString(const char* type_name, std::string_view s, Decimal* out
}
int32_t parsed_precision = static_cast<int32_t>(significant_digits);

// Reject precisions that exceed the target decimal's bit width. ShiftAndAdd
// only carries through the limbs of the output array and silently drops
// the overflow; callers that ignore the out-parameter would get a corrupted
// (mod 2^kBitWidth) value with Status::OK. See GH-49817.
if (parsed_precision > Decimal::kMaxPrecision) {
return Status::Invalid("The string '", s, "' has precision ", parsed_precision,
" which exceeds the ", type_name, " maximum of ",
Decimal::kMaxPrecision);
}

int32_t parsed_scale = 0;
if (dec.has_exponent) {
auto adjusted_exponent = dec.exponent;
Expand Down Expand Up @@ -943,6 +953,14 @@ Status SimpleDecimalFromString(const char* type_name, std::string_view s,
}
int32_t parsed_precision = static_cast<int32_t>(significant_digits);

// Reject precisions that exceed the target decimal's max; ShiftAndAdd into
// a single uint64_t would silently wrap on overflow (GH-49817).
if (parsed_precision > DecimalClass::kMaxPrecision) {
return Status::Invalid("The string '", s, "' has precision ", parsed_precision,
" which exceeds the ", type_name, " maximum of ",
DecimalClass::kMaxPrecision);
}

int32_t parsed_scale = 0;
if (dec.has_exponent) {
auto adjusted_exponent = dec.exponent;
Expand Down