From e3de2b9852d71bb14e770767dd46ab48bb1fdd14 Mon Sep 17 00:00:00 2001
From: Qian Wang <cbeuw.andy@gmail.com>
Date: Wed, 7 Aug 2019 17:22:40 +0100
Subject: [PATCH] Fix a potential make len<0

---
 internal/multiplex/obfs.go | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/internal/multiplex/obfs.go b/internal/multiplex/obfs.go
index 0a18e5e..c997e90 100644
--- a/internal/multiplex/obfs.go
+++ b/internal/multiplex/obfs.go
@@ -89,7 +89,11 @@ func MakeDeobfs(salsaKey [32]byte, payloadCipher cipher.AEAD) Deobfser {
 		closing := header[8]
 		extraLen := header[9]
 
-		outputPayload := make([]byte, len(payload)-int(extraLen))
+		outputLen := len(payload) - int(extraLen)
+		if outputLen < 0 {
+			return nil, errors.New("extra length is greater than total payload length")
+		}
+		outputPayload := make([]byte, outputLen)
 
 		if payloadCipher == nil {
 			copy(outputPayload, payload)