{"id":"CVE-2026-89661","summary":"NFSD: Prevent post-shutdown use-after-free in unlock_filesystem","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nNFSD: Prevent post-shutdown use-after-free in unlock_filesystem\n\nWriting a filesystem path to /proc/fs/nfsd/unlock_filesystem runs\nnfsd4_cancel_copy_by_sb() before nfsd_mutex is held and before the\nhandler confirms that nn-\u003enfsd_serv is set. Once nfsd has shut down,\nnfs4_state_destroy_net() has freed nn-\u003econf_id_hashtbl but left the\npointer intact, so the cancel helper iterates freed slab memory as an\narray of struct list_head and then dereferences a bogus nfs4_client\nwhen it takes clp-\u003easync_lock. A local administrator holding\nCAP_SYS_ADMIN can reach this use-after-free by stopping the server and\nthen writing to unlock_filesystem; KASAN reports a slab-use-after-free\nread in nfsd4_cancel_copy_by_sb().\n\nnfsd4_revoke_states() walks the same state tables and for that reason\nalready runs only under nfsd_mutex with nn-\u003enfsd_serv confirmed\npresent. Move the async COPY cancel into that protected section so\nevery NFSv4 state-table walker on this path observes a running server.\nAsync copies exist only while the server runs, so gating the cancel on\nnn-\u003enfsd_serv loses nothing.","modified":"2026-09-13T03:47:20.167344507Z","published":"2026-09-11T19:45:49.086Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89661.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/0c1a755b7212e0835398d4df5e782ea85ccd7476"},{"type":"WEB","url":"https://git.kernel.org/stable/c/292d915d3ba6fd15eeb88351fa10581683073109"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89661.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89661"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"3daab3112f039cf849f96764019b096bb0a39d04"},{"fixed":"0c1a755b7212e0835398d4df5e782ea85ccd7476"},{"fixed":"292d915d3ba6fd15eeb88351fa10581683073109"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89661.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"7.0.0"},{"fixed":"7.2.4"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89661.json"}}],"schema_version":"1.9.0"}