nfsd4: fix setclientid_confirm same_cred check

New clients are created only by nfsd4_setclientid(), which always gives
any new client a unique clientid.  The only exception is in the
"callback update" case, in which case it may create an unconfirmed
client with the same clientid as a confirmed client.  In that case it
also checks that the confirmed client has the same credential.

Therefore, it is pointless for setclientid_confirm to check whether a
confirmed and unconfirmed client with the same clientid have matching
credentials--they're guaranteed to.

Instead, it should be checking whether the credential on the
setclientid_confirm matches either of those.  Otherwise, it could be
anyone sending the setclientid_confirm.  Granted, I can't see why anyone
would, but still it's probalby safer to check.
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4state.c

@@ -2243,7 +2243,7 @@ nfsd4_setclientid_confirm(struct svc_rqst *rqstp,
 	status = nfserr_clid_inuse;
 	if (conf && unconf && same_verf(&confirm, &unconf->cl_confirm)) {
 		/* case 1: callback update */
-		if (!same_creds(&conf->cl_cred, &unconf->cl_cred))
+		if (!same_creds(&conf->cl_cred, &rqstp->rq_cred))
 			status = nfserr_clid_inuse;
 		else {
 			nfsd4_change_callback(conf, &unconf->cl_cb_conn);