device: make unmarshall length checks exact

This is already enforced in receive.go, but if these unmarshallers are
to have error return values anyway, make them as explicit as possible.

Signed-off-by: Jason A. Donenfeld <[email protected]>

Author: zx2c4

device/noise-protocol.go

@@ -116,11 +116,11 @@ type MessageCookieReply struct {
 	Cookie   [blake2s.Size128 + poly1305.TagSize]byte
 }
 
-var errMessageTooShort = errors.New("message too short")
+var errMessageLengthMismatch = errors.New("message length mismatch")
 
 func (msg *MessageInitiation) unmarshal(b []byte) error {
-	if len(b) < MessageInitiationSize {
-		return errMessageTooShort
+	if len(b) != MessageInitiationSize {
+		return errMessageLengthMismatch
 	}
 
 	msg.Type = binary.LittleEndian.Uint32(b)
@@ -135,8 +135,8 @@ func (msg *MessageInitiation) unmarshal(b []byte) error {
 }
 
 func (msg *MessageResponse) unmarshal(b []byte) error {
-	if len(b) < MessageResponseSize {
-		return errMessageTooShort
+	if len(b) != MessageResponseSize {
+		return errMessageLengthMismatch
 	}
 
 	msg.Type = binary.LittleEndian.Uint32(b)
@@ -151,8 +151,8 @@ func (msg *MessageResponse) unmarshal(b []byte) error {
 }
 
 func (msg *MessageCookieReply) unmarshal(b []byte) error {
-	if len(b) < MessageCookieReplySize {
-		return errMessageTooShort
+	if len(b) != MessageCookieReplySize {
+		return errMessageLengthMismatch
 	}
 
 	msg.Type = binary.LittleEndian.Uint32(b)