dnsmasq: Change behavior when RD bit unset in queries.

Backport upstream commit

Change anti cache-snooping behaviour with queries with the
recursion-desired bit unset. Instead to returning SERVFAIL, we
now always forward, and never answer from the cache. This
allows "dig +trace" command to work.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>

package/network/services/dnsmasq/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=dnsmasq
 PKG_VERSION:=2.80test6
-PKG_RELEASE:=2
+PKG_RELEASE:=3
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=http://thekelleys.org.uk/dnsmasq/test-releases

package/network/services/dnsmasq/patches/0002-Change-behavior-when-RD-bit-unset-in-queries.patch

@@ -0,0 +1,54 @@
+From 4139298d287eb5c57f4aa53c459cb02fc5be2495 Mon Sep 17 00:00:00 2001
+From: Simon Kelley <simon@thekelleys.org.uk>
+Date: Wed, 19 Sep 2018 22:27:11 +0100
+Subject: [PATCH 2/2] Change behavior when RD bit unset in queries.
+
+Change anti cache-snooping behaviour with queries with the
+recursion-desired bit unset. Instead to returning SERVFAIL, we
+now always forward, and never answer from the cache. This
+allows "dig +trace" command to work.
+
+Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
+---
+ CHANGELOG     | 7 ++++++-
+ src/rfc1035.c | 8 +++-----
+ 2 files changed, 9 insertions(+), 6 deletions(-)
+
+--- a/CHANGELOG
++++ b/CHANGELOG
+@@ -59,7 +59,12 @@ version 2.80
+ 	Returning null addresses is a useful technique for ad-blocking.
+ 	Thanks to Peter Russell for the suggestion.
+ 	
+-
++	Change anti cache-snooping behaviour with queries with the
++	recursion-desired bit unset. Instead to returning SERVFAIL, we
++	now always forward, and never answer from the cache. This
++	allows "dig +trace" command to work. 
++	
++	
+ version 2.79
+ 	Fix parsing of CNAME arguments, which are confused by extra spaces.
+ 	Thanks to Diego Aguirre for spotting the bug.
+--- a/src/rfc1035.c
++++ b/src/rfc1035.c
+@@ -1293,16 +1293,14 @@ size_t answer_request(struct dns_header
+   struct mx_srv_record *rec;
+   size_t len;
+ 
+-  if (ntohs(header->ancount) != 0 ||
++  /* never answer queries with RD unset, to avoid cache snooping. */
++  if (!(header->hb3 & HB3_RD) ||
++      ntohs(header->ancount) != 0 ||
+       ntohs(header->nscount) != 0 ||
+       ntohs(header->qdcount) == 0 || 
+       OPCODE(header) != QUERY )
+     return 0;
+ 
+-  /* always servfail queries with RD unset, to avoid cache snooping. */
+-  if (!(header->hb3 & HB3_RD))
+-    return setup_reply(header, qlen, NULL, F_SERVFAIL, 0);
+-  
+   /* Don't return AD set if checking disabled. */
+   if (header->hb4 & HB4_CD)
+     sec_data = 0;