nodejs/node

fs.lchmod opens file with O_WRONLY unnecessarily, fails on directories and non-writable files

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#23,736 opened on Oct 18, 2018

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Description

  • Version: v10.12.0
  • Platform: Darwin geegaw.local 18.0.0 Darwin Kernel Version 18.0.0: Wed Aug 22 20:13:40 PDT 2018; root:xnu-4903.201.2~1/RELEASE_X86_64 x86_64
  • Subsystem: fs

https://github.com/isaacs/chmodr/pull/20

Node's fs.lchmod implementation opens the file in write-only mode. (On Darwin, at least.)

This is unnecessary, and fails for read-only files.

Additionally, this approach (open and then use fchmod) fails for directories. Is there a reason why native lchmod isn't being used? Systems that have O_SYMLINK also have lchmod(3), don't they?

This is important because lchmod is the only way to avoid a (minor) security vulnerability when doing recursive mode setting on directories. If we have to restrict the use of lchmod to only symlinks, then we're back in TOCTOU territory.

Contributor guide

Research direction
Investigate the fs.lchmod implementation in Node.js source (src/node file.cc). Determine if native lchmod is available on the platform and if so, use it directly instead of open+O WRONLY. Also consider the directory case.
Tech stack
nodejs
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
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Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30