[C++][Parquet] Saturate ApplicationVersion components instead of atoi UB

[rootvector2]

What

When reading a Parquet file, ApplicationVersion::ApplicationVersion(const std::string& created_by) parses the writer-supplied created_by metadata string into three integer fields (version.major, version.minor, version.patch). The current implementation in cpp/src/parquet/metadata.cc does this with std::atoi:

application_version_.version.major = atoi(version_major_string.c_str());  // line 1444
application_version_.version.minor = atoi(version_minor_string.c_str());  // line 1469
application_version_.version.patch = atoi(version_patch_string.c_str());  // line 1487

The substrings here are already filtered to be digit-only, but their length is not bounded. The created_by field is fully attacker-controlled in any untrusted Parquet file, so an input like

parquet-mr version 99999999999999999999.0.0 (build abcd)

reaches atoi with a value far outside the range of int. Per the C++ standard, std::atoi has undefined behavior when the result cannot be represented as an int ([c.strtoint]). In practice the value is unspecified, and the negative or otherwise garbage value that comes out then drives VersionLt / HasCorrectStatistics, controlling whether the reader chooses to trust the column statistics block of the file.

How to observe

A small reproducer in the same C++17 mode as Arrow:

#include <cstdio>
#include <cstdlib>
#include <string>
int main() {
    std::string s = "99999999999999999999";
    std::printf("atoi -> %d\n", std::atoi(s.c_str())); // UB; observed -1 here
}

UBSan flags the overflow inside the underlying strtol. The existing tests in metadata_test.cc only cover small inputs, which is why this has not been caught.

The fix

Replace the three atoi call sites with a small ParseUnsignedVersionComponent helper inside the anonymous namespace in metadata.cc. The helper uses std::strtoul (which is defined to set errno = ERANGE and return ULONG_MAX on overflow rather than invoking UB) and saturates to std::numeric_limits<int>::max() when the parsed value would not fit in int. The fix is local to the callee – callers (the constructor of ApplicationVersion, called from FileMetaData's thrift deserializer) are unchanged.

A new ApplicationVersion.VersionComponentOverflow test exercises:

• very long all-digit components (saturate to INT_MAX),
• exactly INT_MAX (representable),
• INT_MAX + 1 (saturates).

Build/test evidence

Built parquet_objlib and parquet-internals-test locally; all 18 ApplicationVersion.* tests pass, including the new overflow case:

[----------] 18 tests from ApplicationVersion (0 ms total)
[  PASSED  ] 18 tests.

[github-actions]

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See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[Copilot]

Pull request overview

This PR hardens Parquet created_by parsing in C++ by removing undefined behavior when version components overflow int, preventing attacker-controlled metadata from producing garbage version values that could affect reader decisions (e.g., statistics trust).

Changes:

• Replaced std::atoi parsing of major/minor/patch with a helper that uses std::strtoul and saturates to INT_MAX on overflow.
• Added a regression test covering very large version components and INT_MAX boundary conditions.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
cpp/src/parquet/metadata.cc	Adds a safe, saturating parser for version components and wires it into ApplicationVersion parsing.
cpp/src/parquet/metadata_test.cc	Adds a new test ensuring overflow inputs clamp to INT_MAX and checks boundary behavior.

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