[SCSI] libiscsi_tcp: fix max_r2t manipulation

Problem description from Xi Wang:
A large max_r2t could lead to integer overflow in subsequent call to
iscsi_tcp_r2tpool_alloc(), allocating a smaller buffer than expected
and leading to out-of-bounds write.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/cxgbi/libcxgbi.c

@@ -2148,11 +2148,10 @@ int cxgbi_set_conn_param(struct iscsi_cls_conn *cls_conn,
 			enum iscsi_param param, char *buf, int buflen)
 {
 	struct iscsi_conn *conn = cls_conn->dd_data;
-	struct iscsi_session *session = conn->session;
 	struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
 	struct cxgbi_conn *cconn = tcp_conn->dd_data;
 	struct cxgbi_sock *csk = cconn->cep->csk;
-	int value, err = 0;
+	int err;
 
 	log_debug(1 << CXGBI_DBG_ISCSI,
 		"cls_conn 0x%p, param %d, buf(%d) %s.\n",
@@ -2174,15 +2173,7 @@ int cxgbi_set_conn_param(struct iscsi_cls_conn *cls_conn,
 							conn->datadgst_en, 0);
 		break;
 	case ISCSI_PARAM_MAX_R2T:
-		sscanf(buf, "%d", &value);
-		if (value <= 0 || !is_power_of_2(value))
-			return -EINVAL;
-		if (session->max_r2t == value)
-			break;
-		iscsi_tcp_r2tpool_free(session);
-		err = iscsi_set_param(cls_conn, param, buf, buflen);
-		if (!err && iscsi_tcp_r2tpool_alloc(session))
-			return -ENOMEM;
+		return iscsi_tcp_set_max_r2t(conn, buf);
 	case ISCSI_PARAM_MAX_RECV_DLENGTH:
 		err = iscsi_set_param(cls_conn, param, buf, buflen);
 		if (!err)