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GHSA-G6RC-QHH9-WVWV

Vulnerability from github – Published: 2026-08-15 06:32 – Updated: 2026-08-23 15:33
VLAI
Details

In the Linux kernel, the following vulnerability has been resolved:

9p: skip nlink update in cacheless mode to fix WARN_ON

v9fs_dec_count() unconditionally calls drop_nlink() on regular files, even when the inode's nlink is already zero. In cacheless mode the client refetches inode metadata from the server (the source of truth) on every operation, so by the time v9fs_remove() returns, the locally cached nlink may already reflect the post-unlink value:

  1. Client initiates unlink, server processes it and sets nlink to 0
  2. Client refetches inode metadata (nlink=0) before unlink returns
  3. Client's v9fs_remove() completes successfully
  4. Client calls v9fs_dec_count() which calls drop_nlink() on nlink=0

This race is easily triggered under heavy unlink workloads, such as stress-ng's unlink stressor, producing the following warning:

WARNING: fs/inode.c:417 at drop_nlink+0x4c/0xc8 Call trace: drop_nlink+0x4c/0xc8 v9fs_remove+0x1e0/0x250 [9p] v9fs_vfs_unlink+0x20/0x38 [9p] vfs_unlink+0x13c/0x258 ...

In cacheless mode the server is authoritative and the inode is on its way out, so locally adjusting nlink buys nothing. Skip v9fs_dec_count() entirely when neither CACHE_META nor CACHE_LOOSE is set, which both avoids the warning and removes a class of nlink races (two concurrent unlinkers observing nlink > 0 and both calling drop_nlink()) that an nlink == 0 guard alone would only narrow rather than close.

Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-72170"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-15T06:21:35Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\n9p: skip nlink update in cacheless mode to fix WARN_ON\n\nv9fs_dec_count() unconditionally calls drop_nlink() on regular files,\neven when the inode\u0027s nlink is already zero. In cacheless mode the\nclient refetches inode metadata from the server (the source of truth)\non every operation, so by the time v9fs_remove() returns, the locally\ncached nlink may already reflect the post-unlink value:\n\n  1. Client initiates unlink, server processes it and sets nlink to 0\n  2. Client refetches inode metadata (nlink=0) before unlink returns\n  3. Client\u0027s v9fs_remove() completes successfully\n  4. Client calls v9fs_dec_count() which calls drop_nlink() on nlink=0\n\nThis race is easily triggered under heavy unlink workloads, such as\nstress-ng\u0027s unlink stressor, producing the following warning:\n\n  WARNING: fs/inode.c:417 at drop_nlink+0x4c/0xc8\n  Call trace:\n   drop_nlink+0x4c/0xc8\n   v9fs_remove+0x1e0/0x250 [9p]\n   v9fs_vfs_unlink+0x20/0x38 [9p]\n   vfs_unlink+0x13c/0x258\n   ...\n\nIn cacheless mode the server is authoritative and the inode is on its\nway out, so locally adjusting nlink buys nothing. Skip v9fs_dec_count()\nentirely when neither CACHE_META nor CACHE_LOOSE is set, which both\navoids the warning and removes a class of nlink races (two concurrent\nunlinkers observing nlink \u003e 0 and both calling drop_nlink()) that an\nnlink == 0 guard alone would only narrow rather than close.",
  "id": "GHSA-g6rc-qhh9-wvwv",
  "modified": "2026-08-23T15:33:00Z",
  "published": "2026-08-15T06:32:14Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-72170"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/4ec4ebe40c82cb4c60756732f6593055d010c59c"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/574aa0b4799470ac814479f1138d19efe6262255"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6086469f7d469549bfd070348b717a6e43736200"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8d610017c992de705b304d3d727a6e3a86af6149"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8faccac11e1369adddf5d80f4a45af93f13b2e1a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a5a682b016ef5b5384e28f6d652d47a8f8e73d37"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ab257019cb72f467b55c95384d99c94e3908b928"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/de79c3f3643841b8659a71958df7cf2a66bfd409"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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