CVE-2026-89660

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

NFSD: Prevent client use-after-free during admin state revocation

A stateid holds only a bare pointer to its nfs4_client; a stateid

reference does not pin it. The client survives only because

__destroy_client() drains its stateids before free_client() runs.

nfsd4_revoke_states() drops nn->client_lock across revoke_one_stid(),

which dereferences the client to revoke a stateid and read

clp->cl_minorversion. A teardown racing the dropped lock can free

the client first.

Pinning cl_rpc_users under client_lock blocks the DESTROY_CLIENTID and

EXCHANGE_ID teardown, which refuses while cl_rpc_users is non-zero.

force_expire_client() ignores it: once its wait for cl_rpc_users to

reach zero has passed, a later pin goes unnoticed.

Under client_lock, skip a client whose cl_time is already zero --

force_expire_client() clears it there before waiting -- otherwise pin

cl_rpc_users before dropping the lock. The walk then either sees the

expiry and skips, or pins in time for that wait to cover the revoke.