fix: prevent use-after-free risk in dual reallocation

[nh13]

Summary

• Check each realloc return value immediately before the next allocation
• Fixed in both occurrences in generate_errors_flows()

Closes #98

Test plan

• Build succeeds
• Integration tests pass

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved error handling and reporting for memory allocation failures, providing more granular diagnostic messages when buffer expansion encounters issues during data processing.

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📝 Walkthrough

Walkthrough

The changes refactor memory allocation error checking in generate_errors_flows() to validate each buffer reallocation independently instead of performing both operations before checking results. Two separate allocation sites are updated to check and assign each pointer immediately after its realloc call, preventing potential use-after-free scenarios.

Changes

Cohort / File(s)	Summary
Memory allocation validation src/dwgsim.c	Split combined realloc error check into granular per-pointer validation in two locations (seq/mask buffer expansion). Each realloc now checked immediately before the next allocation, with distinct error messages for seq and mask failures.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 Hop hop, a fix so neat and fine,
Two checks now dance in perfect line,
No more use-after-free's sneaky call,
Each buffer checked before the fall!
Memory safe, our code runs strong,
The rabbit's path has been all along! 🥕

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: prevent use-after-free risk in dual reallocation' directly summarizes the main objective of the PR: addressing a use-after-free vulnerability when reallocating memory buffers.
Linked Issues check	✅ Passed	The PR changes correctly implement the proposed fix from issue #98: checking each realloc return value immediately and assigning before the next allocation, eliminating the use-after-free risk in both code locations.
Out of Scope Changes check	✅ Passed	All changes are scoped to the linked issue #98 objectives: the modifications only affect memory allocation error checking in generate_errors_flows() with no extraneous changes.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/use-after-free-reallocation

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📜 Recent review details

Configuration used: defaults

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 26e3aa9 and 1d8a4d3.

📒 Files selected for processing (1)

• src/dwgsim.c

🔇 Additional comments (2)

src/dwgsim.c (2)

293-308: LGTM! Proper fix for use-after-free risk.

The refactor correctly addresses the issue by checking and assigning each realloc result immediately before performing the next allocation. This prevents the inconsistent state that could occur if temp_mask realloc failed after temp_seq succeeded. The specific error messages for each buffer are also an improvement.

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374-389: LGTM! Second occurrence correctly fixed.

This second allocation site applies the same safe pattern: each realloc is checked and assigned independently, eliminating the use-after-free risk. The implementation is consistent with the first occurrence.

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