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From a3303e196e5d304ec955c4d63afb923ade66c6e8 Mon Sep 17 00:00:00 2001
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From: Simon Kelley <simon@thekelleys.org.uk>
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Date: Thu, 7 Sep 2017 20:45:00 +0100
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Subject: [PATCH] Don't return arcount=1 if EDNS0 RR won't fit in the packet.
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Omitting the EDNS0 RR but setting arcount gives a malformed packet.
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Also, don't accept UDP packet size less than 512 in recieved EDNS0.
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---
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src/edns0.c | 5 ++++-
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src/forward.c | 2 ++
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2 files changed, 6 insertions(+), 1 deletion(-)
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diff --git a/src/edns0.c b/src/edns0.c
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index 3fde17f..f5b798c 100644
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--- a/src/edns0.c
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+++ b/src/edns0.c
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@@ -208,7 +208,10 @@ size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *l
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free(buff);
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p += rdlen;
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}
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- header->arcount = htons(ntohs(header->arcount) + 1);
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+
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+ /* Only bump arcount if RR is going to fit */
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+ if (((ssize_t)optlen) <= (limit - (p + 4)))
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+ header->arcount = htons(ntohs(header->arcount) + 1);
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}
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if (((ssize_t)optlen) > (limit - (p + 4)))
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diff --git a/src/forward.c b/src/forward.c
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index e3fa94b..942b02d 100644
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--- a/src/forward.c
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+++ b/src/forward.c
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@@ -1412,6 +1412,8 @@ void receive_query(struct listener *listen, time_t now)
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defaults to 512 */
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if (udp_size > daemon->edns_pktsz)
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udp_size = daemon->edns_pktsz;
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+ else if (udp_size < PACKETSZ)
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+ udp_size = PACKETSZ; /* Sanity check - can't reduce below default. RFC 6891 6.2.3 */
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}
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#ifdef HAVE_AUTH
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--
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2.9.5
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