log: mem: signv4: Plug possible memory errors

[cosmo0920]

Closes: #12205.

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Testing
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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

  • Improved log-cache handling when memory allocation fails.
  • Prevented oversized messages from causing invalid suppression checks.
  • Preserved existing cached content when updates cannot be allocated.
  • Improved cleanup after query formatting failures to prevent resource leaks.

• Tests

  • Added fuzz testing for log-cache creation, message handling, duplicate suppression, oversized inputs, and allocation failures.

[coderabbitai]

📝 Walkthrough

Walkthrough

This change hardens log-cache allocation and copy failure paths, adds an INT_MAX size guard, adds an OSS-Fuzz target with allocator fault injection, and cleans up resources when SignV4 query formatting fails.

Changes

Log cache hardening

Layer / File(s)	Summary
Log cache failure-path fixes src/flb_log.c	Adds allocation cleanup, an INT_MAX suppression guard, and failure-safe SDS buffer replacement.
OSS-Fuzz log cache coverage tests/internal/fuzzers/CMakeLists.txt, tests/internal/fuzzers/log_cache_fuzzer.c, include/fluent-bit/flb_mem.h	Registers a log-cache fuzzer and exercises suppression, oversized messages, and injected allocation failures.

SignV4 query cleanup

Layer / File(s)	Summary
Query formatting failure cleanup src/flb_signv4.c	Frees allocated query-formatting resources before returning on failure.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Suggested reviewers: edsiper

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 12.50% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The change frees the unlinked entry, destroys the partial cache, and returns on SDS allocation failure, satisfying issue #12205.
Out of Scope Changes check	✅ Passed	The fuzzing support and SignV4 cleanup address related allocation-failure paths and remain within the PR objectives.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the log, memory, and SignV4 memory-error fixes covered by the pull request.

✨ Finishing Touches 💡 1

📝 Generate docstrings 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch cosmo0920-plug-memory-errors

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/flb_log.c`:
- Around line 704-706: Move every listed control-block opening brace to its own
following line without changing behavior: update the if in src/flb_log.c lines
704-706; the for and if blocks in tests/internal/fuzzers/log_cache_fuzzer.c
lines 58-69, both if blocks at lines 86-96, and the if blocks at lines 106-108,
120-122, and 128-131; and the if in include/fluent-bit/flb_mem.h lines 103-105.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: fd421061-9453-4dd7-a34b-e06e8e5ef4bc

📥 Commits

Reviewing files that changed from the base of the PR and between cf50b7e and 32ab6f5.

📒 Files selected for processing (4)

• include/fluent-bit/flb_mem.h
• src/flb_log.c
• tests/internal/fuzzers/CMakeLists.txt
• tests/internal/fuzzers/log_cache_fuzzer.c