1 From a3303e196e5d304ec955c4d63afb923ade66c6e8 Mon Sep 17 00:00:00 2001
2 From: Simon Kelley <simon@thekelleys.org.uk>
3 Date: Thu, 7 Sep 2017 20:45:00 +0100
4 Subject: [PATCH] Don't return arcount=1 if EDNS0 RR won't fit in the packet.
6 Omitting the EDNS0 RR but setting arcount gives a malformed packet.
7 Also, don't accept UDP packet size less than 512 in recieved EDNS0.
11 2 files changed, 6 insertions(+), 1 deletion(-)
13 diff --git a/src/edns0.c b/src/edns0.c
14 index 3fde17f..f5b798c 100644
17 @@ -208,7 +208,10 @@ size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *l
21 - header->arcount = htons(ntohs(header->arcount) + 1);
23 + /* Only bump arcount if RR is going to fit */
24 + if (((ssize_t)optlen) <= (limit - (p + 4)))
25 + header->arcount = htons(ntohs(header->arcount) + 1);
28 if (((ssize_t)optlen) > (limit - (p + 4)))
29 diff --git a/src/forward.c b/src/forward.c
30 index e3fa94b..942b02d 100644
33 @@ -1412,6 +1412,8 @@ void receive_query(struct listener *listen, time_t now)
35 if (udp_size > daemon->edns_pktsz)
36 udp_size = daemon->edns_pktsz;
37 + else if (udp_size < PACKETSZ)
38 + udp_size = PACKETSZ; /* Sanity check - can't reduce below default. RFC 6891 6.2.3 */