CVE-2026-89662

Summary

In the Linux kernel, the following vulnerability has been resolved:

NFSD: Prevent lock owner use-after-free during client teardown

__destroy_client() releases a client's open owners, but a lock owner whose only reference is a blocked lock (nbl) stays on cl_ownerstr_hashtbl. client_has_state() does not count a bare owner, so DESTROY_CLIENTID can reach __destroy_client() with such owners present.

__destroy_client() then walks the table, calling remove_blocked_locks() on each owner without a reference. Freeing a blocked lock drops the owner reference held via flc_owner. The per-net laundromat reaps blocked locks from nn->blocked_locks_lru independently of client state. The two paths share blocked_locks_lock only for the list splice, not the owner's lifetime. The laundromat therefore frees the owner as __destroy_client() dereferences it, a NULL dereference in remove_blocked_locks().

nfsd4_release_lockowner() holds a reference across the same call; __destroy_client() does not. Hold cl_lock across the walk, taking a reference and unhashing each owner, then drop it before remove_blocked_locks() and nfs4_put_stateowner(), which take blocked_locks_lock and cl_lock.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/a6ead6fff3a7d03e49845f048f7000a2e0d34431
• https://git.kernel.org/stable/c/4804c58f73a80d12df1de323bf97a164f6ee8743
• https://git.kernel.org/stable/c/8cf4ff0a7c083dd5e0067f517d63979b74b66649
• https://git.kernel.org/stable/c/5e2fa29d223a9a1e6a948e40b109d09081d1decd

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