{"id":"CVE-2026-72170","revision":"c7ad2cca3def4e08a8766d24a23db521","records":[{"revision":"c7ad2cca3def4e08a8766d24a23db521","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-72170","aliases":[],"title":"9p: skip nlink update in cacheless mode to fix WARN_ON","description":"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 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.","state":0,"publishedAt":"2026-08-15T05:53:36.332+00:00","modifiedAt":"2026-10-16T18:45:00.097+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"fs/9p/vfs_inode.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"ac89b2ef9b55924bcf922251f043ba73a32d05bb\",\n                            \"lessThan\": \"6086469f7d469549bfd070348b717a6e43736200\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"ac89b2ef9b55924bcf922251f043ba73a32d05bb\",\n                            \"lessThan\": \"ab257019cb72f467b55c95384d99c94e3908b928\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"ac89b2ef9b55924bcf922251f043ba73a32d05bb\",\n                            \"lessThan\": \"4ec4ebe40c82cb4c60756732f6593055d010c59c\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"ac89b2ef9b55924bcf922251f043ba73a32d05bb\",\n                            \"lessThan\": \"a5a682b016ef5b5384e28f6d652d47a8f8e73d37\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"ac89b2ef9b55924bcf922251f043ba73a32d05bb\",\n                            \"lessThan\": \"de79c3f3643841b8659a71958df7cf2a66bfd409\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"ac89b2ef9b55924bcf922251f043ba73a32d05bb\",\n                            \"lessThan\": \"8d610017c992de705b304d3d727a6e3a86af6149\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"ac89b2ef9b55924bcf922251f043ba73a32d05bb\",\n                            \"lessThan\": \"8faccac11e1369adddf5d80f4a45af93f13b2e1a\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"ac89b2ef9b55924bcf922251f043ba73a32d05bb\",\n                            \"lessThan\": \"574aa0b4799470ac814479f1138d19efe6262255\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        }\n                    ]\n                }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"affected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"fs/9p/vfs_inode.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"4.17\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \"0\",\n                            \"lessThan\": \"4.17\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"5.10.266\",\n                            \"lessThanOrEqual\": \"5.10.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"5.15.217\",\n                            \"lessThanOrEqual\": \"5.15.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.1.184\",\n                            \"lessThanOrEqual\": \"6.1.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.6.145\",\n                            \"lessThanOrEqual\": \"6.6.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.12.97\",\n                            \"lessThanOrEqual\": \"6.12.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.18.40\",\n                            \"lessThanOrEqual\": \"6.18.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.1.5\",\n                            \"lessThanOrEqual\": \"7.1.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.2\",\n                            \"lessThanOrEqual\": \"*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"original_commit_for_fix\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","score":7.8,"severity":"HIGH"}],"references":["https://git.kernel.org/stable/c/6086469f7d469549bfd070348b717a6e43736200","https://git.kernel.org/stable/c/ab257019cb72f467b55c95384d99c94e3908b928","https://git.kernel.org/stable/c/4ec4ebe40c82cb4c60756732f6593055d010c59c","https://git.kernel.org/stable/c/a5a682b016ef5b5384e28f6d652d47a8f8e73d37","https://git.kernel.org/stable/c/de79c3f3643841b8659a71958df7cf2a66bfd409","https://git.kernel.org/stable/c/8d610017c992de705b304d3d727a6e3a86af6149","https://git.kernel.org/stable/c/8faccac11e1369adddf5d80f4a45af93f13b2e1a","https://git.kernel.org/stable/c/574aa0b4799470ac814479f1138d19efe6262255"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-72170","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-72170","identifiers":["CVE-2026-72170"]},"retained":false,"historicalAffected":[]}],"coverage":[]}