DEBIAN-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 nfs4client 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 nfs4putstateowner() takes the client's cllock. Because the laundromat detaches the nbl first, destroyclient() no longer finds it, so a concurrent forceexpireclient() can free the client before nfs4putstateowner() runs, dereferencing cllock 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->blockedlockslock. Every other site holds nn->blockedlockslock as a leaf, acquiring no further lock, so placing nn->clientlock outside it cannot form a lock-order cycle.