From 5cf802eda080d438d5aa707886cc3715b55b1694 Mon Sep 17 00:00:00 2001
From: sg <goldsimon@gmx.de>
Date: Mon, 7 Mar 2016 19:47:39 +0100
Subject: [PATCH] dns_gethostbyname: return error code if no valid server is
 set instead of calling the 'found' callback in this case (fixes bug #46887)

---
 src/core/dns.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/core/dns.c b/src/core/dns.c
index d442cd12..4a1678d3 100644
--- a/src/core/dns.c
+++ b/src/core/dns.c
@@ -1474,6 +1474,11 @@ dns_gethostbyname_addrtype(const char *hostname, ip_addr_t *addr, dns_found_call
   LWIP_UNUSED_ARG(dns_addrtype);
 #endif /* LWIP_IPV4 && LWIP_IPV6 */
 
+  /* prevent calling found callback if no server is set, return error instead */
+  if (ip_addr_isany_val(dns_servers[0])) {
+    return ERR_VAL;
+  }
+
   /* queue query with specified callback */
   return dns_enqueue(hostname, hostnamelen, found, callback_arg LWIP_DNS_ADDRTYPE_ARG(dns_addrtype));
 }