CVE-2026-89662

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.