From 23526aec1d933b6362c80eaa084749a794d43aca Mon Sep 17 00:00:00 2001
From: Miek Gieben <miek@miek.nl>
Date: Fri, 29 Sep 2017 22:27:40 +0100
Subject: [PATCH] core: drop invalid packets (#1123)

We can still be on the receiving end of invalid packet. Drop them
here.
---
 core/dnsserver/server.go | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/core/dnsserver/server.go b/core/dnsserver/server.go
index f24b1dd60..721fd216e 100644
--- a/core/dnsserver/server.go
+++ b/core/dnsserver/server.go
@@ -179,6 +179,13 @@ func (s *Server) Address() string { return s.Addr }
 // defined in the request so that the correct zone
 // (configuration and plugin stack) will handle the request.
 func (s *Server) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) {
+	// our dns library protects us against really invalid packets, we can still
+	// get semi valid packets. Drop them here.
+	if r == nil || len(r.Question) == 0 {
+		DefaultErrorFunc(w, r, dns.RcodeServerFailure)
+		return
+	}
+
 	if !s.debug {
 		defer func() {
 			// In case the user doesn't enable error plugin, we still