nfsd4: setclientid_confirm with unmatched verifier should fail

A setclientid_confirm with (clientid, verifier) both matching an
existing confirmed record is assumed to be a replay, but if the verifier
doesn't match, it shouldn't be.

This would be a very rare case, except that clients following
https://tools.ietf.org/html/rfc7931#section-5.8 may depend on the
failure.
Reviewed-by: NJeff Layton <jlayton@redhat.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4state.c

@@ -3304,9 +3304,10 @@ nfsd4_setclientid_confirm(struct svc_rqst *rqstp,
 		goto out;
 	/* cases below refer to rfc 3530 section 14.2.34: */
 	if (!unconf || !same_verf(&confirm, &unconf->cl_confirm)) {
-		if (conf && !unconf) /* case 2: probable retransmit */
+		if (conf && same_verf(&confirm, &conf->cl_confirm)) {
+			/* case 2: probable retransmit */
 			status = nfs_ok;
-		else /* case 4: client hasn't noticed we rebooted yet? */
+		} else /* case 4: client hasn't noticed we rebooted yet? */
 			status = nfserr_stale_clientid;
 		goto out;
 	}