lez-fuzzing/docs/fuzzing.md

Fuzzing Guide

This document covers how to run fuzz targets, add new targets, minimise failures, and convert findings into regression tests.

The fuzzing infrastructure lives in a separate repository (lez-fuzzing/) which reads the Logos Execution Zone (LEZ) codebase from ../logos-execution-zone/ (a sibling directory that must be cloned separately).

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Prerequisites

# Rust nightly is required by cargo-fuzz / libFuzzer
rustup install nightly
rustup component add llvm-tools-preview --toolchain nightly

cargo install cargo-fuzz

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Repository Setup

lez-fuzzing is a standalone repository — it does not use git submodules. It expects the LEZ codebase to be cloned at ../logos-execution-zone relative to itself.

# Clone both repositories side-by-side into the same parent directory:
git clone <LEZ_REPO_URL>           logos-execution-zone
git clone <LEZ_FUZZING_REPO_URL>   lez-fuzzing

# The directory layout must be:
#   <parent>/
#   ├── logos-execution-zone/
#   └── lez-fuzzing/

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How to Run

All fuzz targets must be run with RISC0_DEV_MODE=1 to disable expensive ZK proof generation. The just recipes handle this automatically.

# From lez-fuzzing/

# Run all targets for 30 s each
just fuzz

# Run a specific target for 120 s
RISC0_DEV_MODE=1 cargo fuzz run fuzz_state_transition -- -max_total_time=120

# Run the saved corpus (regression mode, no mutations)
just fuzz-regression

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Available Fuzz Targets

Target	What it fuzzes	Entry point
fuzz_transaction_decoding	borsh decoding of all transaction and block types	fuzz/fuzz_targets/fuzz_transaction_decoding.rs
fuzz_stateless_verification	transaction_stateless_check() signature validation	fuzz/fuzz_targets/fuzz_stateless_verification.rs
fuzz_state_transition	V03State::transition_from_*() with invariant checks	fuzz/fuzz_targets/fuzz_state_transition.rs
fuzz_block_verification	Block hash integrity + replayer pipeline	fuzz/fuzz_targets/fuzz_block_verification.rs

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How to Add a New Fuzz Target

1. Create fuzz/fuzz_targets/fuzz_<name>.rs using the template below.
2. Add a [[bin]] entry to fuzz/Cargo.toml.
3. Create an empty seed corpus directory: mkdir -p fuzz/corpus/fuzz_<name>.
4. Add the target to the CI matrix in .github/workflows/fuzz.yml.
5. Run RISC0_DEV_MODE=1 cargo fuzz build fuzz_<name> to verify it compiles.

Template:

#![no_main]
use libfuzzer_sys::fuzz_target;

fuzz_target!(|data: &[u8]| {
    // 1. Parse / decode `data` into your target type
    // 2. Call the function under test
    // 3. Assert invariants using `fuzz_props::invariants::assert_invariants()`
    // 4. Never panic on invalid input; only panic on invariant violations
});

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Updating the LEZ Dependency

lez-fuzzing reads LEZ source directly from ../logos-execution-zone. To pick up LEZ changes, simply update that repo:

cd ../logos-execution-zone
git pull --ff-only
cd ../lez-fuzzing

# Rebuild to confirm compatibility:
cargo build -p fuzz_props
RISC0_DEV_MODE=1 cargo fuzz build

The just update-lez recipe automates the pull:

just update-lez

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Minimising & Reproducing Failures

When cargo fuzz finds a crash it writes an artifact to fuzz/artifacts/fuzz_<target>/crash-<hash>.

Minimise

# Produces a smaller input that still triggers the same crash
just fuzz-tmin fuzz_state_transition fuzz/artifacts/fuzz_state_transition/crash-abc123

Convert to a regression test

# Print the bytes as a Rust byte-literal (paste into a #[test])
cargo fuzz fmt fuzz_state_transition fuzz/artifacts/fuzz_state_transition/crash-abc123

Add the minimised file to the corpus so CI always reproduces it:

cp fuzz/artifacts/fuzz_state_transition/crash-abc123-minimised \
   fuzz/corpus/fuzz_state_transition/regression_001

Open a PR. The regression CI job will permanently block re-introduction of this bug.

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Invariant Framework

Shared invariants live in fuzz_props/src/invariants.rs. Each invariant implements ProtocolInvariant and is automatically run by assert_invariants().

To add a new invariant:

1. Add a zero-size struct implementing ProtocolInvariant.
2. Register it in the invariants slice inside assert_invariants().
3. Write a #[test] in fuzz_props that triggers and detects a synthetic violation.

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Performance Baseline

Measured on a 4-core x86_64 Linux runner with RISC0_DEV_MODE=1:

Target	Throughput
fuzz_transaction_decoding	~200 000 exec/sec
fuzz_stateless_verification	~30 000 exec/sec
fuzz_state_transition	~5 000 exec/sec
fuzz_block_verification	~50 000 exec/sec

Recommended local settings for longer runs:

# Use all available cores
RISC0_DEV_MODE=1 cargo fuzz run fuzz_state_transition \
  -- -max_total_time=3600 -jobs=$(nproc) -workers=$(nproc)

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ZK-Proof Cost Warning

PrivacyPreservingTransaction uses risc0-zkvm (seconds per proof). All fuzz targets must set RISC0_DEV_MODE=1 in the environment and the just recipes handle this automatically via:

export RISC0_DEV_MODE := "1"

Do not invoke full proof generation inside any fuzz target. The RISC0_DEV_MODE=1 flag stubs out ZK proof generation and replaces it with a fast mock implementation.

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Input Generators

The fuzz_props crate (fuzz_props/src/generators.rs) provides reusable input generators for both libfuzzer (via arbitrary) and proptest:

Generator	Covers
arbitrary_transaction()	IS-2: malformed + boundary transactions
arb_borsh_transaction_bytes()	IS-2: raw borsh bytes including invalid encodings
arb_invalid_account_state_tx()	IS-3: phantom accounts + overflow amounts
arb_duplicate_tx_sequence()	IS-4: duplicated + re-ordered transaction sequences
arb_pathological_sequence()	IS-5: zero-value, self-transfer, max-nonce inputs

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Known Limitations & Future Work

Item	Notes
PrivacyPreservingTransaction coverage	Currently only exercised in decoding target; a dedicated slow target with RISC0_DEV_MODE=1 and proptest should be added after the four MVP targets are stable
V03State snapshot equality	If V03State does not implement PartialEq/Clone, implement or derive them in lez/nssa/src/state.rs behind a cfg(any(test, feature = "fuzzing")) guard
AFL++ integration	A just fuzz-afl recipe can be added later; the same corpus is compatible
Differential testing (sequencer vs replayer)	Add a fifth target that feeds the same block to SequencerCore and indexer_core and asserts identical state roots
LEZ version tracking	There is no submodule pin — lez-fuzzing reads ../logos-execution-zone as checked out. Update that repo to a release tag or a tested commit, then run just update-lez (which does git pull --ff-only) and open a PR to bump it.