From 079db13938c0c208bfefaf0201363977ec5f6fa7 Mon Sep 17 00:00:00 2001
From: Ondrej Mikle <ondrej.mikle@gmail.com>
Date: Tue, 28 Dec 2021 22:38:05 +0100
Subject: [PATCH] Fix race condition when card is removed during read and
 libfreefare returns list of just NULL pointer

---
 nfc_smartcard.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/nfc_smartcard.cpp b/nfc_smartcard.cpp
index 8a04328..930b8fb 100644
--- a/nfc_smartcard.cpp
+++ b/nfc_smartcard.cpp
@@ -165,6 +165,10 @@ std::string NFCDevice::readDesfireNDEF() throw(NFCError)
     if (!tags) {
         throw NFCError("No tags detected");
     }
+    // freefare_get_tags() returns a NULL-terminated list of MifareTag
+    if (!*tags) {
+        throw NFCError("Empty array tag, bailing out");
+    }
     MifareTag& tag = *tags; //only first one is used
 
     if (DESFIRE != freefare_get_tag_type (tag)) {