From 4a5c0ed4e2e1784dab9869f91e9feaabe8c1cc43 Mon Sep 17 00:00:00 2001
From: "John J. Jordan" <jj@jjjordan.io>
Date: Tue, 3 Apr 2018 02:10:47 -0700
Subject: [PATCH] Prevent underflow in tag reader

---
 src/MACLib/APETag.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/MACLib/APETag.cpp b/src/MACLib/APETag.cpp
index 435d9a6..2fedcbe 100644
--- src/MACLib/APETag.cpp
+++ src/MACLib/APETag.cpp
@@ -504,7 +504,8 @@ int CAPETag::LoadField(const char * pBuffer, int nMaximumBytes, int * pBytes)
     
     // safety check (so we can't get buffer overflow attacked)
     int nMaximumRead = nMaximumBytes - 8 - nFieldValueSize;
-    BOOL bSafe = TRUE;
+    // guard against underflow
+    BOOL bSafe = nMaximumRead > 0;
     for (int z = 0; (z < nMaximumRead) && (bSafe == TRUE); z++)
     {
         int nCharacter = pBuffer[nLocation + z];