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Fix parsing when CNAME is provided for MX query

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The code was assuming that the record type was
MX even though this could be false. Also adjusted
some code to also make it easier to test.

Note: the behavior when MX records are missing
is probably still not right.

Closes PR 13654

original commit: c7d878c009
This commit is contained in:
Asumu Takikawa 2013-04-10 17:13:04 -04:00
parent e37893aa04
commit 0d0c10d9c4
2 changed files with 92 additions and 18 deletions
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24
collects/net/dns.rkt
View File

@ -214,6 +214,11 @@
timeout))
(lambda (v) (retry (* timeout 2)))))))
(lambda () (udp-close udp))))
(parse-reply query reply))
;; Parse a DNS query reply
(define (parse-reply query reply)
;; First two bytes must match sent message id:
(unless (and (= (car reply) (car query))
(= (cadr reply) (cadr query)))
@ -361,24 +366,31 @@
(or (try-forwarding
(lambda (nameserver)
(let-values ([(auth? qds ans nss ars reply) (dns-query/cache nameserver addr 'mx 'in)])
(values (let loop ([ans ans][best-pref +inf.0][exchanger #f])
(values (parse-mx-response ans nss reply addr) ars auth?)))
nameserver)
(error 'dns-get-mail-exchanger "bad address")))
;; helper that parses a response for MX queries
(define (parse-mx-response ans nss reply addr)
(let loop ([ans ans] [best-pref +inf.0] [exchanger #f])
(cond
[(null? ans)
(or (and exchanger (bytes->string/latin-1 exchanger))
;; Does 'soa mean that the input address is fine?
;; FIXME: Does 'soa mean that the input address is fine?
(and (ormap (lambda (ns) (eq? (rr-type ns) 'soa))
nss)
addr))]
[else
(define type (rr-type (car ans)))
(define d (rr-data (car ans)))
(cond [(not (eq? type 'mx)) ; not MX record, keep going
(loop (cdr ans) best-pref exchanger)]
[else
(define pref (octet-pair->number (car d) (cadr d)))
(if (< pref best-pref)
(let-values ([(name start) (parse-name (cddr d) reply)])
(loop (cdr ans) pref name))
(loop (cdr ans) best-pref exchanger))]))
ars auth?)))
nameserver)
(error 'dns-get-mail-exchanger "bad address")))
(loop (cdr ans) best-pref exchanger))])])))
(define (dns-find-nameserver)
(case (system-type)

66
collects/tests/net/dns.rkt
View File

@ -3,8 +3,66 @@
(require net/dns tests/eli-tester)
;; internal tests
(define mx-response-with-cname
'(;; random ID
0 187
;; QR Opcode AA TC RD RA Z RCODE
;; 1 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0
129 128
;; QDCOUNT
0 1
;; ANSCOUNT
0 1
;; NSCOUNT
0 1
;; ARCOUNT
0 0
;; QNAME (stat.ethz.ch)
4 115 116 97 116
4 101 116 104 122
2 99 104 0
;; QTYPE (MX)
0 15
;; QCLASS (IN)
0 1
;; NAME (pointer)
;; 1100000000001100
192 12
;; TYPE: CNAME
0 5
;; CLASS
0 1
;; TTL
0 0
4 79
;; RDLENGTH
0 19
;; RDATA
11 109 97 103 101 108 108 97 110 45 48 54
4 109 97 116 104
192 17
;; NAME (pointer)
192 17
;; TYPE: SOA
0 6
;; CLASS
0 1
;; TTL
0 0 1 90
;; RDLENGTH & DATA
0 44 8 100 117 109 109 121 45
110 115 192 17 10 104 111 115 116 109
97 115 116 101 114 192 17 119 168 176
33 0 0 42 48 0 0 14 16 0 27 175 128 0 0 2 88))
(require (only-in rackunit require/expose) net/private/ip)
(require/expose net/dns (ip->in-addr.arpa ip->ip6.arpa))
(require/expose net/dns (ip->in-addr.arpa ip->ip6.arpa
parse-reply parse-mx-response))
(define-values (_1 _2 mx-ans mx-nss _3 _4)
(parse-reply '(0 187 129 128) mx-response-with-cname))
(define (internal-tests)
(test (ip->in-addr.arpa (ipv4 (bytes 8 8 8 8)))
=> "8.8.8.8.in-addr.arpa"
@ -15,7 +73,11 @@
".2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.ip6.arpa")
(ip->ip6.arpa (make-ip-address "2001:db8::567:89ab"))
=> (string-append "b.a.9.8.7.6.5.0.0.0.0.0.0.0.0.0"
".0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa")))
".0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa")
;; FIXME: may need to change if SOA handling in net/dns
;; changes (see FIXME there)
(parse-mx-response mx-ans mx-nss mx-response-with-cname "stat.ethz.ch")
=> "stat.ethz.ch"))
;; Constants for testing. These can go out of sync
;; when server setups change, so keep them up-to-date.