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MINOR: dns: no expected DNS record type found

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Some DNS responses may be valid from a protocol point of view, but may
not contain any information considered as interested by the requester..
Purpose of the flag DNS_RESP_NO_EXPECTED_RECORD introduced by this patch is
to allow reporting such situation.

When this happens, a new DNS query is sent with a new query type.

For now, the function only expect A and AAAA query types which is enough
to cover current cases.
In a next future, it will be up to the caller to tell the function which
query types are expected.
This commit is contained in:
Baptiste Assmann 2015-09-09 00:46:58 +02:00 committed by Willy Tarreau
parent 5554e2983d
commit 96972bcd36
3 changed files with 19 additions and 1 deletions
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1
include/types/dns.h
View File

@ -199,6 +199,7 @@ enum {
DNS_RESP_CNAME_ERROR, /* error when resolving a CNAME in an atomic response */
DNS_RESP_TIMEOUT, /* DNS server has not answered in time */
DNS_RESP_TRUNCATED, /* DNS response is truncated */
DNS_RESP_NO_EXPECTED_RECORD, /* No expected records were found in the response */
};
/* return codes after searching an IP in a DNS response buffer, using a family preference */

18
src/dns.c
View File

@ -222,6 +222,11 @@ void dns_resolve_recv(struct dgram_conn *dgram)
nameserver->counters.truncated += 1;
resolution->requester_error_cb(resolution, DNS_RESP_TRUNCATED);
continue;
case DNS_RESP_NO_EXPECTED_RECORD:
nameserver->counters.other += 1;
resolution->requester_error_cb(resolution, DNS_RESP_NO_EXPECTED_RECORD);
continue;
}
nameserver->counters.valid += 1;
@ -334,12 +339,18 @@ void dns_update_resolvers_timeout(struct dns_resolvers *resolvers)
int dns_validate_dns_response(unsigned char *resp, unsigned char *bufend, char *dn_name, int dn_name_len)
{
unsigned char *reader, *cname, *ptr;
int i, len, flags, type, ancount, cnamelen;
int i, len, flags, type, ancount, cnamelen, expected_record;
reader = resp;
cname = NULL;
cnamelen = 0;
len = 0;
expected_record = 0; /* flag to report if at least one expected record type is found in the response.
* For now, only records containing an IP address (A and AAAA) are
* considered as expected.
* Later, this function may be updated to let the caller decide what type
* of record is expected to consider the response as valid. (SRV or TXT types)
*/
/* move forward 2 bytes for the query id */
reader += 2;
@ -540,6 +551,7 @@ int dns_validate_dns_response(unsigned char *resp, unsigned char *bufend, char *
/* ipv4 is stored on 4 bytes */
if (len != 4)
return DNS_RESP_INVALID;
expected_record = 1;
break;
case DNS_RTYPE_CNAME:
@ -551,6 +563,7 @@ int dns_validate_dns_response(unsigned char *resp, unsigned char *bufend, char *
/* ipv6 is stored on 16 bytes */
if (len != 16)
return DNS_RESP_INVALID;
expected_record = 1;
break;
} /* switch (record type) */
@ -558,6 +571,9 @@ int dns_validate_dns_response(unsigned char *resp, unsigned char *bufend, char *
reader += len;
} /* for i 0 to ancount */
if (expected_record == 0)
return DNS_RESP_NO_EXPECTED_RECORD;
return DNS_RESP_VALID;
}

1
src/server.c
View File

@ -2120,6 +2120,7 @@ int snr_resolution_error_cb(struct dns_resolution *resolution, int error_code)
case DNS_RESP_ANCOUNT_ZERO:
case DNS_RESP_TRUNCATED:
case DNS_RESP_ERROR:
case DNS_RESP_NO_EXPECTED_RECORD:
qtype_any = resolution->query_type == DNS_RTYPE_ANY;
res_preferred_afinet = resolution->resolver_family_priority == AF_INET && resolution->query_type == DNS_RTYPE_A;
res_preferred_afinet6 = resolution->resolver_family_priority == AF_INET6 && resolution->query_type == DNS_RTYPE_AAAA;