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->blockedlockslru -- 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 flcowner, and the final nfs4put_stateowner()

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

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

forceexpireclient() can free the client before nfs4putstateowner()

runs, dereferencing cl_lock in freed memory.

Pin the client with clrpcusers before dropping

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

blocked locks _destroyclient() frees while holding an owner

reference. Take nn->clientlock outside nn->blockedlocks_lock.

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

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

a lock-order cycle.