Validate indices in set cover file readers to prevent OOB access

[TristanInSec]

Summary

The ORLIB SCP/Rail readers and solution text/proto readers accept file-derived integer values as array indices without validating that they are non-negative and in range.

• ReadOrlibScp: 1-indexed subset values are converted to 0-indexed via ParseNextInteger() - 1. A file value of 0 produces SubsetIndex(-1).
• ReadOrlibRail: Same pattern for element indices.
• ReadSetCoverSolutionText: 0-indexed subset values are used directly without range checking.
• ReadSetCoverSolutionProto: Same pattern.

When the signed BaseInt (int32_t) is negative, StrongVector::operator[] casts it to size_t, producing a massive offset that causes out-of-bounds heap access. The existing guard in AddElementToSubset (subset >= num_subsets()) does not catch negative values because -1 >= 0 evaluates to false for signed comparison.

Changes

• Add CHECK_GE validation in each reader function to reject invalid indices from file input before they reach the model.
• Add CHECK_LT for solution readers to validate indices are within the declared range.
• Add defense-in-depth CHECK_GE in AddElementToSubset to catch negative element/subset indices from any caller.

Affected files

• ortools/set_cover/set_cover_reader.cc (4 reader functions)
• ortools/set_cover/set_cover_model.cc (AddElementToSubset)

[Mizux]

please send PR against main branch our devlopment branch, stable is just pointing to last release tag

[TristanInSec]

please send PR against main branch our devlopment branch, stable is just pointing to last release tag

Done. Thanks.