🛡️ Sentinel: [보안 개선] 입력 경로 길이를 제한하여 DoS 및 OOM 방지

[seonghobae]

이 PR은 유효 보안 delta가 없어 병합하지 않고 종료합니다. 동일한 4,096-character cap 가설은 canonical repair lane #598에서 realistic RED로 반증했고, portable filesystem contract로 교정했습니다.

이 branch의 전체 semantic delta는 세 가지뿐입니다: go()에 require(topDir.length <= 4096) 추가, 4,097자 문자열이 IllegalArgumentException을 내야 한다는 테스트, 그리고 이를 MEDIUM DoS/OOM 방어라고 일반화한 Sentinel journal입니다. 이 셋은 같은 검증되지 않은 전제를 공유합니다.

문제는 Kotlin String.length == 4097 자체가 OOM/DoS 경계라는 근거가 없고, pathname 제약은 OS/filesystem별로 다르다는 점입니다. Java File의 pathname 변환은 system-dependent이며 POSIX/Windows pathname semantics도 동일한 고정 4,096-character 애플리케이션 invariant를 제공하지 않습니다. 따라서 이 변경은 정상 입력을 임의로 거부할 수 있고 실제 resource-exhaustion 원인(directory count/fan-out/generated bytes/filesystem calls/elapsed time/peak RSS)을 다루지 않습니다.

Canonical repair #598의 current lineage는 반대 계약을 명시적으로 고정합니다: 4,097자라는 이유만으로 별도 path-length 오류를 내지 않으며, arbitrary 4,096 gate를 제거하고, 실제 large-tree resource behavior를 별도 product/technical Gap으로 추적합니다. #598 exact head b18b1de3bf881ef51c863050ff5abf3b6df1625a는 Draft이고 exact-head CI/security가 아직 non-terminal이므로 그것 역시 merge-ready로 간주하지 않습니다.

Primary references:

• Oracle Java SE 21 java.io.File: pathname string ↔ abstract pathname conversion is system-dependent — https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/io/File.html
• Microsoft Win32 maximum path documentation — https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation
• POSIX pathconf()/PATH_MAX/NAME_MAX/ENAMETOOLONG semantics — https://man7.org/linux/man-pages/man3/fpathconf.3p.html

따라서 #608에는 successor로 승계해야 할 독립적인 유효 test/fixture/contract가 없습니다. false-positive security claim과 그 claim만 검증하는 source/test를 제거하는 것이 올바른 처리이며, 실제 DoS/OOM 문제는 #598에 기록된 측정 가능한 resource-budget Gap에서 다룹니다.

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📥 Commits

Reviewing files that changed from the base of the PR and between 55b39b4 and 48d3d2d.

📒 Files selected for processing (3)

• .jules/sentinel.md
• src/main/kotlin/html4tree/main.kt
• src/test/kotlin/html4tree/MainTest.kt

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

[cwl-noema-review]

Noema LLM review

The PR adds a 4096-character length guard at the start of go() to mitigate DoS/OOM via oversized topDir inputs. The check is placed before any file-system access, includes a boundary-appropriate comparison, and is covered by a new test for 4097-character paths. No regressions were observed for normal-length paths.

Reviewed changed lines

• src/main/kotlin/html4tree/main.kt:138 (RIGHT): The require(topDir.length <= 4096) guard runs before isNotBlank, traversal checks, File construction, and Files.isDirectory. This correctly blocks oversized inputs at the earliest point and prevents resource-intensive operations.
• src/test/kotlin/html4tree/MainTest.kt:130 (RIGHT): The new test constructs a 4097-character path and asserts IllegalArgumentException, matching the intended behavior. It may reach other guards after the length check, but the failure still validates the new security control.
• .jules/sentinel.md:102 (RIGHT): The sentinel note correctly documents the vulnerability, learning, and prevention guidance for bounded input length before expensive file-system operations.

Adversarial validation

• src/main/kotlin/html4tree/main.kt:138 (RIGHT) falsified: A path of exactly 4096 characters is rejected by the new length check. — The comparison uses <=, so exactly 4096 characters passes. Subsequent validation proceeds normally.
• src/main/kotlin/html4tree/main.kt:138 (RIGHT) falsified: A path of 4097 characters reaches file-system operations before being rejected. — The new require statement is the first line in go() and throws IllegalArgumentException immediately, before any file-system access.
• src/main/kotlin/html4tree/main.kt:138 (RIGHT) falsified: The new guard breaks previously accepted normal-length paths. — The check only rejects inputs longer than 4096 characters; normal short paths remain unaffected.
• Residual risk: No concrete regression hypothesis was falsified by the probes; the length check is placed before all file-system calls and is covered by a boundary test.

Findings

• No blocking findings.

• Result: APPROVE
• Head SHA: 48d3d2d7e745146d285f21f894ca409ef610a941
• Reviewer credential: noema-review-github-app-refresh
• Actor: cwl-noema-review[bot]