CVE-2026-90036

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

NFSD: Prevent client use-after-free during blocked-lock reaping

A bare lock owner -- its only remaining reference a blocked lock on

nn->blocked_locks_lru -- holds a raw pointer to its nfs4_client but

no reference keeping the client alive. When the per-net laundromat

reaps such a lock, freeing the nbl drops the owner reference

held through flc_owner, and the final nfs4_put_stateowner()

takes the client's cl_lock. Because the laundromat detaches the

nbl first, __destroy_client() no longer finds it, so a concurrent

force_expire_client() can free the client before nfs4_put_stateowner()

runs, dereferencing cl_lock in freed memory.

Pin the client with cl_rpc_users before dropping

nn->blocked_locks_lock, and skip clients already expiring, whose

blocked locks __destroy_client() frees while holding an owner

reference. Take nn->client_lock outside nn->blocked_locks_lock.

Every other site holds nn->blocked_locks_lock as a leaf, acquiring

no further lock, so placing nn->client_lock outside it cannot form

a lock-order cycle.