support anonymous auth

Signed-off-by: Avi Deitcher <avi@deitcher.net>

client.go

@@ -46,11 +46,6 @@ func (d *Dialer) DialContext(ctx context.Context, tcpConn net.Conn) (*Session, e
 	if d.Initiator == nil {
 		return nil, &InternalError{"Initiator is empty"}
 	}
-	if i, ok := d.Initiator.(*NTLMInitiator); ok {
-		if i.User == "" {
-			return nil, &InternalError{"Anonymous account is not supported yet. Use guest account instead"}
-		}
-	}
 
 	maxCreditBalance := d.MaxCreditBalance
 	if maxCreditBalance == 0 {

internal/ntlm/challengemessage.go

@@ -0,0 +1,83 @@
+package ntlm
+
+import (
+	"bytes"
+	"errors"
+
+	"github.com/cloudsoda/go-smb2/internal/utf16le"
+)
+
+type ChallengeMessage struct {
+	raw        []byte
+	flags      uint32
+	info       *targetInfoEncoder
+	targetName []byte
+}
+
+// Unmarshal parses the ChallengeMessage in cmsg and returns the result.
+func UnmarshalChallengeMessage(cmsg, nmsg []byte, targetSPN string) (*ChallengeMessage, error) {
+	//        ChallengeMessage
+	//   0-8: Signature
+	//  8-12: MessageType
+	// 12-20: TargetNameFields
+	// 20-24: NegotiateFlags
+	// 24-32: ServerChallenge
+	// 32-40: _
+	// 40-48: TargetInfoFields
+	// 48-56: Version
+	//   56-: Payload
+	if len(cmsg) < 48 {
+		return nil, errors.New("message length is too short")
+	}
+
+	if !bytes.Equal(cmsg[:8], signature) {
+		return nil, errors.New("invalid signature")
+	}
+
+	if le.Uint32(cmsg[8:12]) != NtLmChallenge {
+		return nil, errors.New("invalid message type")
+	}
+
+	flags := le.Uint32(nmsg[12:16]) & le.Uint32(cmsg[20:24])
+
+	if flags&NTLMSSP_REQUEST_TARGET == 0 {
+		return nil, errors.New("invalid negotiate flags")
+	}
+
+	targetNameLen := le.Uint16(cmsg[12:14])    // cmsg.TargetNameLen
+	targetNameMaxLen := le.Uint16(cmsg[14:16]) // cmsg.TargetNameMaxLen
+	if targetNameMaxLen < targetNameLen {
+		return nil, errors.New("invalid target name format")
+	}
+	targetNameBufferOffset := le.Uint32(cmsg[16:20]) // cmsg.TargetNameBufferOffset
+	if len(cmsg) < int(targetNameBufferOffset+uint32(targetNameLen)) {
+		return nil, errors.New("invalid target name format")
+	}
+	targetName := cmsg[targetNameBufferOffset : targetNameBufferOffset+uint32(targetNameLen)] // cmsg.TargetName
+
+	if flags&NTLMSSP_NEGOTIATE_TARGET_INFO == 0 {
+		return nil, errors.New("invalid negotiate flags")
+	}
+
+	targetInfoLen := le.Uint16(cmsg[40:42])    // cmsg.TargetInfoLen
+	targetInfoMaxLen := le.Uint16(cmsg[42:44]) // cmsg.TargetInfoMaxLen
+	if targetInfoMaxLen < targetInfoLen {
+		return nil, errors.New("invalid target info format")
+	}
+	targetInfoBufferOffset := le.Uint32(cmsg[44:48]) // cmsg.TargetInfoBufferOffset
+	if len(cmsg) < int(targetInfoBufferOffset+uint32(targetInfoLen)) {
+		return nil, errors.New("invalid target info format")
+	}
+	targetInfo := cmsg[targetInfoBufferOffset : targetInfoBufferOffset+uint32(targetInfoLen)] // cmsg.TargetInfo
+	info := newTargetInfoEncoder(targetInfo, utf16le.Encode(targetSPN, utf16le.MapCharsNone))
+	if info == nil {
+		return nil, errors.New("invalid target info format")
+	}
+
+	return &ChallengeMessage{
+		raw:        cmsg,
+		flags:      flags,
+		info:       info,
+		targetName: targetName,
+	}, nil
+}