telebit/vendor/github.com/jcmturner/gokrb5/v8/client/network.go

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2020-06-03 06:18:04 +00:00
package client
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"io"
"net"
"time"
"github.com/jcmturner/gokrb5/v8/iana/errorcode"
"github.com/jcmturner/gokrb5/v8/messages"
)
// SendToKDC performs network actions to send data to the KDC.
func (cl *Client) sendToKDC(b []byte, realm string) ([]byte, error) {
var rb []byte
if cl.Config.LibDefaults.UDPPreferenceLimit == 1 {
//1 means we should always use TCP
rb, errtcp := cl.sendKDCTCP(realm, b)
if errtcp != nil {
if e, ok := errtcp.(messages.KRBError); ok {
return rb, e
}
return rb, fmt.Errorf("communication error with KDC via TCP: %v", errtcp)
}
return rb, nil
}
if len(b) <= cl.Config.LibDefaults.UDPPreferenceLimit {
//Try UDP first, TCP second
rb, errudp := cl.sendKDCUDP(realm, b)
if errudp != nil {
if e, ok := errudp.(messages.KRBError); ok && e.ErrorCode != errorcode.KRB_ERR_RESPONSE_TOO_BIG {
// Got a KRBError from KDC
// If this is not a KRB_ERR_RESPONSE_TOO_BIG we will return immediately otherwise will try TCP.
return rb, e
}
// Try TCP
r, errtcp := cl.sendKDCTCP(realm, b)
if errtcp != nil {
if e, ok := errtcp.(messages.KRBError); ok {
// Got a KRBError
return r, e
}
return r, fmt.Errorf("failed to communicate with KDC. Attempts made with UDP (%v) and then TCP (%v)", errudp, errtcp)
}
rb = r
}
return rb, nil
}
//Try TCP first, UDP second
rb, errtcp := cl.sendKDCTCP(realm, b)
if errtcp != nil {
if e, ok := errtcp.(messages.KRBError); ok {
// Got a KRBError from KDC so returning and not trying UDP.
return rb, e
}
rb, errudp := cl.sendKDCUDP(realm, b)
if errudp != nil {
if e, ok := errudp.(messages.KRBError); ok {
// Got a KRBError
return rb, e
}
return rb, fmt.Errorf("failed to communicate with KDC. Attempts made with TCP (%v) and then UDP (%v)", errtcp, errudp)
}
}
return rb, nil
}
// dialKDCTCP establishes a UDP connection to a KDC.
func dialKDCUDP(count int, kdcs map[int]string) (*net.UDPConn, error) {
i := 1
for i <= count {
udpAddr, err := net.ResolveUDPAddr("udp", kdcs[i])
if err != nil {
return nil, fmt.Errorf("error resolving KDC address: %v", err)
}
conn, err := net.DialTimeout("udp", udpAddr.String(), 5*time.Second)
if err == nil {
if err := conn.SetDeadline(time.Now().Add(5 * time.Second)); err != nil {
return nil, err
}
// conn is guaranteed to be a UDPConn
return conn.(*net.UDPConn), nil
}
i++
}
return nil, errors.New("error in getting a UDP connection to any of the KDCs")
}
// dialKDCTCP establishes a TCP connection to a KDC.
func dialKDCTCP(count int, kdcs map[int]string) (*net.TCPConn, error) {
i := 1
for i <= count {
tcpAddr, err := net.ResolveTCPAddr("tcp", kdcs[i])
if err != nil {
return nil, fmt.Errorf("error resolving KDC address: %v", err)
}
conn, err := net.DialTimeout("tcp", tcpAddr.String(), 5*time.Second)
if err == nil {
if err := conn.SetDeadline(time.Now().Add(5 * time.Second)); err != nil {
return nil, err
}
// conn is guaranteed to be a TCPConn
return conn.(*net.TCPConn), nil
}
i++
}
return nil, errors.New("error in getting a TCP connection to any of the KDCs")
}
// sendKDCUDP sends bytes to the KDC via UDP.
func (cl *Client) sendKDCUDP(realm string, b []byte) ([]byte, error) {
var r []byte
count, kdcs, err := cl.Config.GetKDCs(realm, false)
if err != nil {
return r, err
}
conn, err := dialKDCUDP(count, kdcs)
if err != nil {
return r, err
}
r, err = cl.sendUDP(conn, b)
if err != nil {
return r, err
}
return checkForKRBError(r)
}
// sendKDCTCP sends bytes to the KDC via TCP.
func (cl *Client) sendKDCTCP(realm string, b []byte) ([]byte, error) {
var r []byte
count, kdcs, err := cl.Config.GetKDCs(realm, true)
if err != nil {
return r, err
}
conn, err := dialKDCTCP(count, kdcs)
if err != nil {
return r, err
}
rb, err := cl.sendTCP(conn, b)
if err != nil {
return r, err
}
return checkForKRBError(rb)
}
// sendUDP sends bytes to connection over UDP.
func (cl *Client) sendUDP(conn *net.UDPConn, b []byte) ([]byte, error) {
var r []byte
defer conn.Close()
_, err := conn.Write(b)
if err != nil {
return r, fmt.Errorf("error sending to (%s): %v", conn.RemoteAddr().String(), err)
}
udpbuf := make([]byte, 4096)
n, _, err := conn.ReadFrom(udpbuf)
r = udpbuf[:n]
if err != nil {
return r, fmt.Errorf("sending over UDP failed to %s: %v", conn.RemoteAddr().String(), err)
}
if len(r) < 1 {
return r, fmt.Errorf("no response data from %s", conn.RemoteAddr().String())
}
return r, nil
}
// sendTCP sends bytes to connection over TCP.
func (cl *Client) sendTCP(conn *net.TCPConn, b []byte) ([]byte, error) {
defer conn.Close()
var r []byte
// RFC 4120 7.2.2 specifies the first 4 bytes indicate the length of the message in big endian order.
var buf bytes.Buffer
err := binary.Write(&buf, binary.BigEndian, uint32(len(b)))
if err != nil {
return r, err
}
b = append(buf.Bytes(), b...)
_, err = conn.Write(b)
if err != nil {
return r, fmt.Errorf("error sending to KDC (%s): %v", conn.RemoteAddr().String(), err)
}
sh := make([]byte, 4, 4)
_, err = conn.Read(sh)
if err != nil {
return r, fmt.Errorf("error reading response size header: %v", err)
}
s := binary.BigEndian.Uint32(sh)
rb := make([]byte, s, s)
_, err = io.ReadFull(conn, rb)
if err != nil {
return r, fmt.Errorf("error reading response: %v", err)
}
if len(rb) < 1 {
return r, fmt.Errorf("no response data from KDC %s", conn.RemoteAddr().String())
}
return rb, nil
}
// checkForKRBError checks if the response bytes from the KDC are a KRBError.
func checkForKRBError(b []byte) ([]byte, error) {
var KRBErr messages.KRBError
if err := KRBErr.Unmarshal(b); err == nil {
return b, KRBErr
}
return b, nil
}