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Change behavior when RD bit unset in queries.

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Change anti cache-snooping behaviour with queries with the
recursion-desired bit unset. Instead to returning SERVFAIL, we
now always forward, and never answer from the cache. This
allows "dig +trace" command to work.
This commit is contained in:
Simon Kelley
2018-09-19 22:27:11 +01:00
parent 51cc10fa54
commit 4139298d28
2 changed files with 9 additions and 6 deletions
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5
CHANGELOG
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@@ -59,6 +59,11 @@ version 2.80
Returning null addresses is a useful technique for ad-blocking. Returning null addresses is a useful technique for ad-blocking.
Thanks to Peter Russell for the suggestion. Thanks to Peter Russell for the suggestion.
Change anti cache-snooping behaviour with queries with the
recursion-desired bit unset. Instead to returning SERVFAIL, we
now always forward, and never answer from the cache. This
allows "dig +trace" command to work.
version 2.79 version 2.79
Fix parsing of CNAME arguments, which are confused by extra spaces. Fix parsing of CNAME arguments, which are confused by extra spaces.

8
src/rfc1035.c
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@@ -1293,16 +1293,14 @@ size_t answer_request(struct dns_header *header, char *limit, size_t qlen,
struct mx_srv_record *rec; struct mx_srv_record *rec;
size_t len; size_t len;
if (ntohs(header->ancount) != 0 || /* never answer queries with RD unset, to avoid cache snooping. */
if (!(header->hb3 & HB3_RD) ||
ntohs(header->ancount) != 0 ||
ntohs(header->nscount) != 0 || ntohs(header->nscount) != 0 ||
ntohs(header->qdcount) == 0 || ntohs(header->qdcount) == 0 ||
OPCODE(header) != QUERY ) OPCODE(header) != QUERY )
return 0; return 0;
/* always servfail queries with RD unset, to avoid cache snooping. */
if (!(header->hb3 & HB3_RD))
return setup_reply(header, qlen, NULL, F_SERVFAIL, 0);
/* Don't return AD set if checking disabled. */ /* Don't return AD set if checking disabled. */
if (header->hb4 & HB4_CD) if (header->hb4 & HB4_CD)
sec_data = 0; sec_data = 0;