CVE-2026-90036NFSD: Prevent client use-after-free during blocked-lock reaping

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/0d53a47c913d0bce3b5ec35c28cbcca4d015f33d
• https://git.kernel.org/stable/c/7081224a59a0ca4edcd62c068588f4d900199a18
• https://git.kernel.org/stable/c/cd489b03587378645fe0d20142a33f1ed60bac98
• https://git.kernel.org/stable/c/6fedb2eaff77554ca7a0deffd2e8bc0d6e8b38b0
• https://git.kernel.org/stable/c/9026932ac8be4d0ae01db47f23619a98cc57b671