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

Type: advisorySource: Official CVE List1 source record

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.

Announced Source revision 1
Original source ↗

CVE-2026-72170

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-72170

Linux

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Linux

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb",
        "lessThan": "6086469f7d469549bfd070348b717a6e43736200",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb",
        "lessThan": "ab257019cb72f467b55c95384d99c94e3908b928",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb",
        "lessThan": "4ec4ebe40c82cb4c60756732f6593055d010c59c",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb",
        "lessThan": "a5a682b016ef5b5384e28f6d652d47a8f8e73d37",
        "versionType": "git"
      },
      {
        "status": "affected",
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        "lessThan": "de79c3f3643841b8659a71958df7cf2a66bfd409",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb",
        "lessThan": "8d610017c992de705b304d3d727a6e3a86af6149",
        "versionType": "git"
      },
      {
        "status": "affected",
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        "lessThan": "8faccac11e1369adddf5d80f4a45af93f13b2e1a",
        "versionType": "git"
      },
      {
        "status": "affected",
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        "lessThan": "574aa0b4799470ac814479f1138d19efe6262255",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "fs/9p/vfs_inode.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "4.17"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "4.17",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "5.10.266",
        "versionType": "semver",
        "lessThanOrEqual": "5.10.*"
      },
      {
        "status": "unaffected",
        "version": "5.15.217",
        "versionType": "semver",
        "lessThanOrEqual": "5.15.*"
      },
      {
        "status": "unaffected",
        "version": "6.1.184",
        "versionType": "semver",
        "lessThanOrEqual": "6.1.*"
      },
      {
        "status": "unaffected",
        "version": "6.6.145",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.97",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.18.40",
        "versionType": "semver",
        "lessThanOrEqual": "6.18.*"
      },
      {
        "status": "unaffected",
        "version": "7.1.5",
        "versionType": "semver",
        "lessThanOrEqual": "7.1.*"
      },
      {
        "status": "unaffected",
        "version": "7.2",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "fs/9p/vfs_inode.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2026-72170

Source reference: /cveMetadata/cveId

Publisher severity

high

Source reference: /containers/cna/metrics

Event
#32964 · Revision 1
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Publisher date
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