CVE-2026-89659

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> NFSD: Prevent client use-after-free during delegation revoke<br /> <br /> A delegation stateid holds only a bare pointer to its owning<br /> nfs4_client and does not keep it alive. The client survives its<br /> stateids only because __destroy_client() drains cl_delegations and<br /> cl_revoked before free_client() runs.<br /> <br /> nfs4_laundromat() breaks that invariant: it unhashes an<br /> expired delegation from cl_delegations, drops deleg_lock, then<br /> revoke_delegation() relinks it onto cl_revoked under cl_lock. In that<br /> window the delegation is on neither list, so client_has_state() can<br /> report no remaining state.<br /> <br /> Every teardown path first requires cl_rpc_users to be zero, but<br /> the laundromat holds no such reference. A client whose recalled<br /> delegation has just timed out can therefore reach free_client()<br /> while revoke_delegation() is still about to dereference cl_lock,<br /> a use-after-free.<br /> <br /> Pin the client with cl_rpc_users across the revoke so teardown blocks<br /> until it completes, then reap the delegation from cl_revoked. A client<br /> already expiring reaps its own, so skip it and leave the delegation on<br /> del_recall_lru.