In the Linux kernel, the following vulnerability has been resolved:
NFSD: Prevent client use-after-free during NFSv4.0 revoked-state cleanup
nfs40_clean_admin_revoked() takes a stateid reference under
clp->cl_lock, drops nn->client_lock, and calls
nfsd4_drop_revoked_stid(), which dereferences the stateid’s client
through s->sc_client->cl_lock. The stateid reference does not pin the
client, so a teardown racing the dropped lock can free the client
while nfsd4_drop_revoked_stid() is still using it.
This cleanup runs from the laundromat, so a periodic sweep can race
force_expire_client() driven by a write to the clients//ctl file.
Skip a client that is already expiring and otherwise pin it with
cl_rpc_users under client_lock before dropping the lock, matching
nfsd4_revoke_states().
