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From 2c1aec1e979a209eb2f2b035314a8c973b4ac269 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 7/9] 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 5bdc133..a8d0167 100644
--- a/src/edns0.c
+++ b/src/edns0.c
@@ -221,7 +221,10 @@ 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 9b464d3..0f8f462 100644
--- a/src/forward.c
+++ b/src/forward.c
@@ -1408,6 +1408,8 @@ 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
--
2.9.5