engine: fix memory leaks with parse error handling in parse_string_map_to_list.

[pwhelan]

Summary

There was a CI Fuzz error that surfaced in #10939: https://github.com/fluent/fluent-bit/actions/runs/18024863430/job/51289945754?pr=10939.

This seems to be an indirect memory leak in flb_slist_split_string whenever it encounters parse errors when it returns early.

The only way I was able to reproduce the bug quickly was to artificially produce errors using a magic string I checked for in the very same error handling code.

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Enter [N/A] in the box, if an item is not applicable to your change.

Testing
Before we can approve your change; please submit the following in a comment:

• [N/A] Example configuration file for the change
• [N/A] Debug log output from testing the change

• [N/A] Attached Valgrind output that shows no leaks or memory corruption was found

Backporting

• Backport to latest stable release. (pending)

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

Summary by CodeRabbit

• Bug Fixes
  • Resolved a memory leak in configuration parsing error handling by ensuring resources are properly released on failure. This prevents memory growth when invalid or malformed configurations are processed, improving stability and reliability in long-running deployments. Users may notice reduced memory footprint under error conditions and fewer potential crashes or restarts related to parsing failures.

[coderabbitai]

Walkthrough

Adds cleanup in parse_string_map_to_list error path: when parsing fails (ret == -1), destroy slist contents with flb_slist_destroy(list) before freeing the list to avoid memory leaks.

Changes

Cohort / File(s)	Summary
Memory cleanup on error path src/flb_config_map.c	On parse failure, call flb_slist_destroy(list) before freeing list and returning NULL, ensuring allocated slist elements are released.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Suggested labels

backport to v4.0.x

Suggested reviewers

• koleini
• fujimotos

Poem

I nibble bugs with careful cheer,
A tidy list, now crystal clear.
One hop back, destroy, then free—
No crumbs of leaks left under me.
Code burrow clean, I thump with glee! 🐇✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Title Check	✅ Passed	The title accurately and concisely summarizes the main change by indicating that the patch fixes memory leaks in the parse_string_map_to_list error-handling path, which directly matches the modifications made in src/flb_config_map.c.

✨ Finishing touches

• 📝 Generate Docstrings

🧪 Generate unit tests

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch pwhelan-fix-flb_slist_split_string-mem-leak-parse-error

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[coderabbitai]

Actionable comments posted: 1

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between d21e8de and 4b1daad.

📒 Files selected for processing (1)

• src/flb_slist.c (2 hunks)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (29)

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🔇 Additional comments (1)

src/flb_slist.c (1)

296-300: Duplicate of earlier comment about destroying the caller list

Same concern as the other new flb_slist_destroy() call: it wipes caller state. Please apply the same fix there.