fix: prevent path traversal in file tree and preview APIs

[liuxiaopai-ai]

Summary

The file tree API (/api/files) and file preview API (/api/files/preview) have ineffective path safety checks that could allow reading arbitrary files on the host system.

Problem

/api/files (file tree)

// Current code — always returns true (comparing a path to itself)
if (!isPathSafe(resolvedDir, resolvedDir)) { ... }

/api/files/preview (file preview)

// Current code — always returns true (a file is always inside its parent)
const dir = path.dirname(resolvedPath);
if (!isPathSafe(dir, resolvedPath)) { ... }

This means requests like GET /api/files/preview?path=/etc/passwd will succeed and return the file contents.

Fix

• Added a baseDir query parameter to both APIs. The frontend can pass the session's workingDirectory as the trust boundary.
• When baseDir is provided, the requested path is validated to be within it using the existing isPathSafe() function.
• For /api/files/preview without baseDir, falls back to restricting access to the user's home directory (prevents reading system files like /etc/passwd).
• Backward compatible: existing callers without baseDir continue to work, with the home directory fallback providing a reasonable safety net.

Security Note

CodePilot runs locally so the attack surface is limited, but proper validation prevents accidental exposure when the dev server is bound to non-localhost interfaces or accessed via browser extensions.

Tests

Added 13 unit tests (src/__tests__/unit/files-security.test.ts) covering:

• ✅ Paths within project directory (allowed)
• ✅ Paths outside project directory (blocked)
• ✅ Path traversal via ../ (blocked)
• ✅ Directory prefix attacks (/project vs /project-evil) (blocked)
• ✅ Symlink escape attempts (blocked)
• ✅ System file access (/etc/passwd) (blocked)
• ✅ Edge cases (root path, same path)

All 13 tests pass:

# tests 13
# pass 13
# fail 0

Run with: npx tsx --test src/__tests__/unit/files-security.test.ts

[op7418]

Review: 需要修改后合并

安全修复方向正确，isPathSafe 逻辑修复有价值。但有两个问题需要解决：

1. 无 baseDir 时跳过校验（严重）

/api/files/route.ts 没有 baseDir 参数时完全不做校验（没有 else 分支），旧版前端调用时仍然没有路径校验。与 /api/files/preview 的 fallback 到 home 目录策略不一致。

建议：无 baseDir 时 fallback 到 os.homedir()，与 preview API 保持一致。

2. baseDir 来自客户端可被伪造（中等）

baseDir 通过 URL 查询参数传入，攻击者可设置 baseDir=/ 绕过所有限制。

建议：如果要做安全修复就应做彻底。理想情况下 baseDir 应从服务端 session 获取。至少应添加白名单校验（如限制在 home 目录子路径下）。

3. 测试清理（轻微）

it('cleanup test fixtures', ...) 应用 afterAll() hook 代替。

---

代码质量和测试覆盖都很好，修复上述问题后即可合并。

[liuxiaopai-ai]

已按 review 修改并 rebase 到最新 main：

修改内容：

1. ✅ 无 baseDir 时 fallback 到 homedir
   /api/files/route.ts 现在与 /api/files/preview 一致，无 baseDir 时限制在用户 home 目录下，防止扫描任意系统目录。

2. ✅ baseDir 白名单校验
   两个 API 都新增了 baseDir 本身必须在 home 目录下的校验。baseDir=/ 会返回 403，彻底防止绕过。

3. ✅ 测试清理改用 after() hook
   替换了 it("cleanup...") 为 after()。新增 6 个 baseDir 校验测试，共 18 个测试全部通过。