check mtu setting

transport/internet/kcp/config_json.go

@@ -4,6 +4,9 @@ package kcp
 
 import (
 	"encoding/json"
+	"errors"
+
+	"github.com/v2ray/v2ray-core/common/log"
 )
 
 func (this *Config) UnmarshalJSON(data []byte) error {
@@ -15,6 +18,11 @@ func (this *Config) UnmarshalJSON(data []byte) error {
 		return err
 	}
 	if jsonConfig.Mtu != nil {
+		mtu := *jsonConfig.Mtu
+		if mtu < 576 || mtu > 1460 {
+			log.Error("KCP|Config: Invalid MTU size: ", mtu)
+			return errors.New("Invalid configuration")
+		}
 		this.Mtu = *jsonConfig.Mtu
 	}