From 4e8640b380cf407cbf442f8d37759339e345ace0 Mon Sep 17 00:00:00 2001
From: "Robert.Schreib" <robert.schreib@e-mundo.de>
Date: Wed, 21 Apr 2021 13:49:55 +0200
Subject: [PATCH] Handle case where no old DNS servers exist

---
 osdep/MacDNSHelper.mm | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/osdep/MacDNSHelper.mm b/osdep/MacDNSHelper.mm
index 89384ba28..38e74dc3f 100644
--- a/osdep/MacDNSHelper.mm
+++ b/osdep/MacDNSHelper.mm
@@ -40,9 +40,13 @@ void MacDNSHelper::setDNS(uint64_t nwid, const char *domain, const std::vector<I
     CFStringRef key = CFStringCreateWithCString(NULL, buf, kCFStringEncodingUTF8);
     CFArrayRef list = SCDynamicStoreCopyKeyList(ds, key);
     CFIndex i = 0, j = CFArrayGetCount(list);
-
-    CFPropertyListRef oldDNSServers = SCDynamicStoreCopyValue(ds, (CFStringRef)CFArrayGetValueAtIndex(list, i));
-    if (!CFEqual(oldDNSServers,dict)) {
+    bool dnsServersChanged = true;
+    CFPropertyListRef oldDNSServers = NULL;
+    if (j > 0) {
+        oldDNSServers = SCDynamicStoreCopyValue(ds, (CFStringRef)CFArrayGetValueAtIndex(list, i));
+        dnsServersChanged = !CFEqual(oldDNSServers,dict);
+    }
+    if (dnsServersChanged) {
         bool ret = TRUE;
         if (j <= 0) {
             ret &= SCDynamicStoreAddValue(ds, key, dict);
@@ -53,8 +57,9 @@ void MacDNSHelper::setDNS(uint64_t nwid, const char *domain, const std::vector<I
             fprintf(stderr, "Error writing DNS configuration\n");
         }
     }
-
-    CFRelease(oldDNSServers);
+    if (oldDNSServers != NULL) {
+        CFRelease(oldDNSServers);
+    }
     CFRelease(list);
     CFRelease(key);
     CFRelease(dict);
@@ -67,8 +72,8 @@ void MacDNSHelper::setDNS(uint64_t nwid, const char *domain, const std::vector<I
     delete[] s;
     CFRelease(ds);
 }
-    
-void MacDNSHelper::removeDNS(uint64_t nwid) 
+
+void MacDNSHelper::removeDNS(uint64_t nwid)
 {
     SCDynamicStoreRef ds = SCDynamicStoreCreate(NULL, CFSTR("zerotier"), NULL, NULL);