CVE-2026-89662NFSD: Prevent lock owner use-after-free during client teardown

Official description

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 packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/42d7954b0a1907d4ef122aef94561952a033cdc3
• https://git.kernel.org/stable/c/bb38ff8b4dafbbd1781ad37cd96722fdf2cd972a
• https://git.kernel.org/stable/c/b8bad5a11416b26cc7fd4b18fba46d75ff636558
• https://git.kernel.org/stable/c/1ce74d1b7770e69735e8f8e509807af4ff9c8ee7
• 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