[G1-Sync] Manual knowledge update

2026-05-09 21:08:02 +09:00
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+---
+id: testing-fuzzing-patterns
+title: Fuzzing — 무작위 / 변형 / coverage 기반
+category: Coding
+status: draft
+source_trust_level: B
+verification_status: conceptual
+created_at: 2026-05-09
+updated_at: 2026-05-09
+tags: [testing, fuzzing, security, vibe-coding]
+tech_stack: { language: "TS / Go / Rust", applicable_to: ["Backend"] }
+applied_in: []
+aliases: [fuzzing, AFL, libfuzzer, OSS-Fuzz, coverage-guided, jazzer.js]
+---
+
+# Fuzzing
+
+> 보안 / 안정성 강력. **무작위 / 변형 input → crash / hang / 잘못된 결과 찾기**. Coverage-guided 가 진화 — 새 path 보면 keep. Parser / decoder / network 입력에 강.
+
+## 📖 핵심 개념
+- Random fuzzing: 완전 random.
+- Mutation: seed 변형 (bit flip, splice).
+- Coverage-guided: 새 path 가는 input 보존.
+- Sanitizer: ASAN, UBSAN 같이 — undefined behavior 잡음.
+
+## 💻 코드 패턴
+
+### Go fuzzing (built-in)
+```go
+// parser_test.go
+package parser
+
+import "testing"
+
+func FuzzParse(f *testing.F) {
+    f.Add([]byte(`{"a":1}`)) // seed
+    f.Add([]byte(`{}`))
+
+    f.Fuzz(func(t *testing.T, data []byte) {
+        result, err := Parse(data)
+        if err != nil { return }
+        // 속성: parse 성공 → reformat → 같은 결과
+        rendered := Format(result)
+        result2, err2 := Parse(rendered)
+        if err2 != nil || !equal(result, result2) {
+            t.Fail()
+        }
+    })
+}
+```
+
+```bash
+go test -fuzz=FuzzParse -fuzztime=10s
+```
+
+### Rust fuzzing (cargo-fuzz)
+```rust
+// fuzz/fuzz_targets/parse.rs
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| {
+    let _ = parser::parse(data);
+});
+```
+
+```bash
+cargo fuzz run parse
+```
+
+### TS fuzzing (jazzer.js)
+```ts
+import { instrument } from '@jazzer.js/instrumentor';
+
+export function fuzz(data: Buffer) {
+  try {
+    JSON.parse(data.toString('utf8'));
+  } catch (e) {
+    if (e instanceof SyntaxError) return; // expected
+    throw e; // unexpected — fuzz 가 crash
+  }
+}
+```
+
+```bash
+jazzer fuzz.ts --fuzz=fuzz
+```
+
+### Property + fuzzing
+```ts
+// fast-check 도 일종의 fuzzing
+import fc from 'fast-check';
+
+fc.assert(fc.property(fc.uint8Array(), (data) => {
+  const parsed = myParse(data);
+  if (parsed) {
+    const rendered = myFormat(parsed);
+    expect(myParse(rendered)).toEqual(parsed);
+  }
+}), { numRuns: 10000 });
+```
+
+### Corpus (seed)
+```
+fuzz/corpus/
+  empty
+  simple.json
+  large.json
+  malformed.json
+  edge_cases/
+```
+
+→ Fuzzer 가 시드에서 시작하여 변형.
+
+### CI fuzzing (Go example)
+```yaml
+- name: Fuzz parse
+  run: go test -fuzz=FuzzParse -fuzztime=2m -run=^$ ./parser/
+```
+
+⚠️ 큰 fuzz time = 느림. PR 마다 X — nightly.
+
+### OSS-Fuzz (Google)
+- Open source: 자동 fuzzing 무료.
+- C/C++/Rust/Go/Python/Java/JS.
+- 발견된 버그 reports + auto regression test.
+
+### Fuzz crash 분석
+```bash
+# Fuzzer 가 crash 한 input 저장
+testdata/fuzz/FuzzParse/abc123  # 특정 input 재현
+go test -run=FuzzParse/abc123    # 그 input 만 실행
+```
+
+→ Shrinking 으로 minimal reproduce.
+
+### 보안 use case
+```
+parser:        SQL injection / command injection 입력
+network:       잘못된 packet → buffer overflow
+crypto:        잘못된 signature / key
+file format:   pdf / image / zip 파싱
+```
+
+### Sanitizer (C/C++/Rust)
+```bash
+# AddressSanitizer
+clang -fsanitize=address fuzz.c
+# UndefinedBehaviorSanitizer
+clang -fsanitize=undefined
+# 결합 = 강
+```
+
+## 🤔 의사결정 기준
+| 적합 | 부적합 |
+|---|---|
+| Parser / decoder | Pure 비즈니스 |
+| Network input handler | UI |
+| File format | DB query |
+| Crypto | Test framework |
+| Compiler / interpreter | 단순 fetch wrapper |
+| 보안 critical | Internal-only API |
+
+## ❌ 안티패턴
+- **No corpus**: 발견 느림. 의미 있는 seed.
+- **Crash 후 안 fix**: 기록만, 다시 발생.
+- **CI 매 PR fuzz**: 느림. nightly / weekly.
+- **Random 만 (coverage 무시)**: 같은 path 만.
+- **Fuzz target 가 setup 비싸 (DB)**: 매 input 마다 setup. mock.
+- **External call (HTTP)**: random — 외부 영향. mock.
+- **Deterministic input 만 OK 가정**: 시간 / random / file 영향 — control.
+
+## 🤖 LLM 활용 힌트
+- Parser / decoder = 자연.
+- Property + fuzzing 결합.
+- OSS-Fuzz 같은 자동 plat 활용.
+
+## 🔗 관련 문서
+- [[Testing_Property_Based]]
+- [[Security_OWASP_Top_10_Practical]]
+- [[Testing_Mutation_Testing]]