From a3303e196e5d304ec955c4d63afb923ade66c6e8 Mon Sep 17 00:00:00 2001 From: Simon Kelley 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 -- 2.9.5