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dnsmasq: backport arcount edns0 fix

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Don't return arcount=1 if EDNS0 RR won't fit in the packet.

Omitting the EDNS0 RR but setting arcount gives a malformed packet.
Also, don't accept UDP packet size less than 512 in received EDNS0.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
This commit is contained in:
Kevin Darbyshire-Bryant 2017-09-08 08:56:34 +01:00 committed by Hans Dedecker
parent a7506c0e2b
commit 1d15a03050
2 changed files with 45 additions and 1 deletions
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2
package/network/services/dnsmasq/Makefile
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@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
PKG_NAME:=dnsmasq
PKG_VERSION:=2.77
PKG_RELEASE:=5
PKG_RELEASE:=6
PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
PKG_SOURCE_URL:=http://thekelleys.org.uk/dnsmasq/

44
package/network/services/dnsmasq/patches/030-fix-arcount-edns0-behaviour.patch Normal file
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@ -0,0 +1,44 @@
From a3303e196e5d304ec955c4d63afb923ade66c6e8 Mon Sep 17 00:00:00 2001
From: Simon Kelley <simon@thekelleys.org.uk>
Date: Thu, 7 Sep 2017 20:45:00 +0100
Subject: [PATCH] Don't return arcount=1 if EDNS0 RR won't fit in the packet.
Omitting the EDNS0 RR but setting arcount gives a malformed packet.
Also, don't accept UDP packet size less than 512 in recieved EDNS0.
---
src/edns0.c | 5 ++++-
src/forward.c | 2 ++
2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/src/edns0.c b/src/edns0.c
index 3fde17f..f5b798c 100644
--- a/src/edns0.c
+++ b/src/edns0.c
@@ -208,7 +208,10 @@ size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *l
free(buff);
p += rdlen;
}
- header->arcount = htons(ntohs(header->arcount) + 1);
+
+ /* Only bump arcount if RR is going to fit */
+ if (((ssize_t)optlen) <= (limit - (p + 4)))
+ header->arcount = htons(ntohs(header->arcount) + 1);
}
if (((ssize_t)optlen) > (limit - (p + 4)))
diff --git a/src/forward.c b/src/forward.c
index e3fa94b..942b02d 100644
--- a/src/forward.c
+++ b/src/forward.c
@@ -1412,6 +1412,8 @@ void receive_query(struct listener *listen, time_t now)
defaults to 512 */
if (udp_size > daemon->edns_pktsz)
udp_size = daemon->edns_pktsz;
+ else if (udp_size < PACKETSZ)
+ udp_size = PACKETSZ; /* Sanity check - can't reduce below default. RFC 6891 6.2.3 */
}
#ifdef HAVE_AUTH
--
1.7.10.4