fix(sdk): add bounds check in extract_description to prevent IndexError

[lh1564803535-code]

Summary

Adds bounds checking to extract_description() in ComponentSpec.from_yaml_documents() to prevent an IndexError (CWE-125: Out-of-bounds access) when parsing malformed or crafted component YAML.

Problem

The extract_description() function in sdk/python/kfp/dsl/structures.py has two unguarded index accesses:

1. component_yaml.splitlines()[index_of_heading] - crashes if the YAML has fewer than 3 lines
2. while comments[index][:len(...)] - crashes if the multi-line description loop runs past the end of the file

Any system using the KFP SDK to parse untrusted YAML (CI/CD pipelines, shared component repos, multi-tenant pipeline services) can be crashed with a crafted input.

Reproducer (from issue #13420)

from kfp.components import structures

malicious_yaml = "line0\nline1\n Description: some text\n              continued text"
spec = structures.ComponentSpec.from_yaml_documents(malicious_yaml)
# IndexError: list index out of range

Fix

• Cache splitlines() result once as lines to avoid redundant splitting
• Guard index_of_heading access with len(lines) > index_of_heading
• Add index < len(lines) to the while loop condition
• Replace comments variable with lines for consistency

Tests

Added TestExtractDescriptionBoundsCheck with 5 test cases covering:

• Short YAML with description heading
• Heading at exact end of lines
• Multi-line description exceeding file length
• Empty YAML string
• Exact reproducer from issue [bug] Out-of-bounds IndexError in extract_description when parsing crafted component YAML #13420

All 56 tests in structures_test.py pass (51 existing + 5 new).

Fixes #13420

[google-oss-prow]

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[google-oss-prow]

Hi @lh1564803535-code. Thanks for your PR.

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[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR hardens YAML description extraction against malformed inputs that previously could raise IndexError, and adds regression tests to ensure these cases don’t crash.

Changes:

• Add bounds checks in extract_description() to prevent out-of-range indexing.
• Add unit tests covering multiple malformed YAML shapes reported to trigger IndexError.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
sdk/python/kfp/dsl/structures.py	Adds defensive bounds checks while parsing multi-line description comments.
sdk/python/kfp/dsl/structures_test.py	Adds regression tests ensuring malformed YAML does not raise IndexError.