{"id":"CVE-2026-72170","title":"9p: skip nlink update in cacheless mode to fix WARN_ON","summary":"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's nlink is already zer…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < 6086469f7d469549bfd070348b717a6e43736200","Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < ab257019cb72f467b55c95384d99c94e3908b928","Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < 4ec4ebe40c82cb4c60756732f6593055d010c59c","Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < a5a682b016ef5b5384e28f6d652d47a8f8e73d37","Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < de79c3f3643841b8659a71958df7cf2a66bfd409","Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < 8d610017c992de705b304d3d727a6e3a86af6149","Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < 8faccac11e1369adddf5d80f4a45af93f13b2e1a","Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < 574aa0b4799470ac814479f1138d19efe6262255","Linux 4.17"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-10-16T18:43:16.365463Z"},"published":"2026-08-15","updated":"2026-10-16","sourceUpdated":"2026-10-16T18:45:00.097Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-72170","references":[{"url":"https://git.kernel.org/stable/c/6086469f7d469549bfd070348b717a6e43736200"},{"url":"https://git.kernel.org/stable/c/ab257019cb72f467b55c95384d99c94e3908b928"},{"url":"https://git.kernel.org/stable/c/4ec4ebe40c82cb4c60756732f6593055d010c59c"},{"url":"https://git.kernel.org/stable/c/a5a682b016ef5b5384e28f6d652d47a8f8e73d37"},{"url":"https://git.kernel.org/stable/c/de79c3f3643841b8659a71958df7cf2a66bfd409"},{"url":"https://git.kernel.org/stable/c/8d610017c992de705b304d3d727a6e3a86af6149"},{"url":"https://git.kernel.org/stable/c/8faccac11e1369adddf5d80f4a45af93f13b2e1a"},{"url":"https://git.kernel.org/stable/c/574aa0b4799470ac814479f1138d19efe6262255"}],"tags":["cve.org"],"epss":0.00169,"epssPercentile":0.05788,"ingestedAt":"2026-10-16T19:46:24.425Z","slug":"CVE-2026-72170","body":"## Overview\n\nIn 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's 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's 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's 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 > 0 and both calling drop_nlink()) that an\nnlink == 0 guard alone would only narrow rather than close.\n\n## Affected\n\n- `Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < 6086469f7d469549bfd070348b717a6e43736200`\n- `Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < ab257019cb72f467b55c95384d99c94e3908b928`\n- `Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < 4ec4ebe40c82cb4c60756732f6593055d010c59c`\n- `Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < a5a682b016ef5b5384e28f6d652d47a8f8e73d37`\n- `Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < de79c3f3643841b8659a71958df7cf2a66bfd409`\n- `Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < 8d610017c992de705b304d3d727a6e3a86af6149`\n- `Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < 8faccac11e1369adddf5d80f4a45af93f13b2e1a`\n- `Linux >= ac89b2ef9b55924bcf922251f043ba73a32d05bb < 574aa0b4799470ac814479f1138d19efe6262255`\n- `Linux 4.17`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}