NFSD: Prevent post-shutdown use-after-free in unlock_filesystem

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Summary

CVECVE-2026-89661
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-11 20:19:52 UTC
Updated2026-09-11 20:19:52 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent post-shutdown use-after-free in unlock_filesystem Writing a filesystem path to /proc/fs/nfsd/unlock_filesystem runs nfsd4_cancel_copy_by_sb() before nfsd_mutex is held and before the handler confirms that nn->nfsd_serv is set. Once nfsd has shut down, nfs4_state_destroy_net() has freed nn->conf_id_hashtbl but left the pointer intact, so the cancel helper iterates freed slab memory as an array of struct list_head and then dereferences a bogus nfs4_client when it takes clp->async_lock. A local administrator holding CAP_SYS_ADMIN can reach this use-after-free by stopping the server and then writing to unlock_filesystem; KASAN reports a slab-use-after-free read in nfsd4_cancel_copy_by_sb(). nfsd4_revoke_states() walks the same state tables and for that reason already runs only under nfsd_mutex with nn->nfsd_serv confirmed present. Move the async COPY cancel into that protected section so every NFSv4 state-table walker on this path observes a running server. Async copies exist only while the server runs, so gating the cancel on nn->nfsd_serv loses nothing.

Risk And Classification

EPSS: 0.001890000 probability, percentile 0.086930000 (date 2026-09-14)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 3daab3112f039cf849f96764019b096bb0a39d04 0c1a755b7212e0835398d4df5e782ea85ccd7476 git Not specified
CNA Linux Linux affected 3daab3112f039cf849f96764019b096bb0a39d04 292d915d3ba6fd15eeb88351fa10581683073109 git Not specified
CNA Linux Linux affected 7.0 Not specified
CNA Linux Linux unaffected 7.0 semver Not specified
CNA Linux Linux unaffected 7.2.4 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/0c1a755b7212e0835398d4df5e782ea85ccd7476 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/292d915d3ba6fd15eeb88351fa10581683073109 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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