Fuzz Harness Gen

fuzz-harness-gen

Generate cargo-fuzz targets for Rust cryptographic libraries and applications.

This skill is user-triggered only. It must never be auto-invoked by the audit router or any other skill. Fuzz runs can be expensive (default timeout: 10 minutes per target via FUZZ_TIME_LIMIT and FUZZ_MAX_ITERS).

When to Use

• User explicitly requests fuzz testing
• User invokes this skill by name
• A Phase 2 finding needs additional crash/DoS or logic-divergence evidence

When NOT to Use

• Never auto-trigger from audit flow
• Never run without explicit user request
• Code is not Rust
• cargo-fuzz is not installed (detect and warn)

Prerequisites

Before generating targets, verify cargo-fuzz is available:

cargo fuzz --version 2>/dev/null || echo "ERROR: cargo-fuzz not installed. Install with: cargo install cargo-fuzz"

If not installed, inform the user and stop.

Core Target Categories

1. Deserialization — reject malformed inputs without panic
2. Point decompression — invalid encodings must fail safely
3. Proof verification — malformed proofs should be rejected, not panic
4. Hash and transcript APIs — odd-length/context inputs should fail closed
5. Parser/state transitions — random byte streams should not trigger UB or invariant breaks

Budget and Fallback Controls

• Override fuzz run duration with FUZZ_TIME_LIMIT (default 600)
• Override fuzz iteration cap with FUZZ_MAX_ITERS when deterministic bounds are needed
• Use optional PROPTEST_CASES for lightweight proptest checks when full fuzzing is unavailable

Workflow

Phase 1: Identify fuzz-worthy surfaces

• Read the target code and public APIs
• Prioritize parser, deserializer, verifier, and boundary-heavy functions
• Read references/fuzz-checklist.md for setup requirements

Phase 2: Generate targets

• Read references/target-patterns.md for templates
• Generate fuzz_target! harnesses with minimal adapters
• Seed corpus when available and set FUZZ_TIME_LIMIT / FUZZ_MAX_ITERS bounds

Phase 3: Execute and triage

• Run cargo fuzz run <target> with FUZZ_TIME_LIMIT / FUZZ_MAX_ITERS budget controls
• Classify crashes as panic/DoS vs logic/soundness implications
• Preserve crash artifacts for reproducible PoC evidence
• If fuzzing is unavailable, run bounded proptest checks (PROPTEST_CASES) and label evidence accordingly

Output Contract

Produce fuzzing results that include:

• The generated target code
• The API/property surface being fuzzed
• Run budget and corpus strategy used
• PASS (no crash found in budget) or FAIL (crash/input found)
• If FAIL: minimized crashing input and reproduction command

Reference Index

• references/fuzz-checklist.md
• references/target-patterns.md