GH-49104: [C++] Fix Segfault in SparseCSFIndex::Equals with mismatched dimensions

[AliRana30]

Rationale for This Change

The SparseCSFIndex::Equals method can crash when comparing two sparse indices that have a different number of dimensions. The method iterates over the indices() and indptr() vectors of the current object and accesses the corresponding elements in the other object without first verifying that both objects have matching vector sizes. This can lead to out-of-bounds access and a segmentation fault when the dimension counts differ.

What Changes Are Included in This PR?

This change adds explicit size equality checks for the indices() and indptr() vectors at the beginning of the SparseCSFIndex::Equals method. If the dimensions do not match, the method now safely returns false instead of attempting invalid memory access.

Are These Changes Tested?

Yes. The fix has been validated through targeted reproduction of the crash scenario using mismatched dimension counts, ensuring the method behaves safely and deterministically.

Are There Any User-Facing Changes?

No. This change improves internal safety and robustness without altering public APIs or observable user behavior.

Closes

Closes #49104

GitHub Issue: [C++] Segfault in SparseCSFIndex::Equals with mismatched dimensions #49104

• GitHub Issue: [C++] Segfault in SparseCSFIndex::Equals with mismatched dimensions #49104

[github-actions]

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See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[github-actions]

⚠️ GitHub issue #49104 has been automatically assigned in GitHub to PR creator.

[kou]

Could you add a test for this case?

[AliRana30]

@kou On your request, I have added a new test case, TestEqualityMismatchedDimensions, in
cpp/src/arrow/sparse_tensor_test.cc.

Test details:
This test compares SparseCSFIndex objects with mismatched dimensions (for example, 1D vs 2D) to verify that Equals now safely returns false instead of causing a segfault.

Fix summary:
The fix adds explicit checks for the sizes of indices, indptr, and axis_order before attempting to iterate over them, ensuring safe comparison when dimensions do not match.