lego/acme/dns_challenge.go
Michael Cross 06b3802346 DNS Challenge: Fix handling of CNAMEs
Prior to this commit, the checkDNSPropagation function was exiting
early if the TXT record could not be found on the recursive
nameserver, and thus the authoritative nameservers were not being
queried until after the record showed up on the recursive nameserver
causing a delay.

This commit changes that behaviour so that the authoritative
nameservers are queried on each execution of checkDNSPropagation when
possible.
2016-02-19 21:44:35 +00:00

222 lines
5.4 KiB
Go

package acme
import (
"crypto/sha256"
"encoding/base64"
"errors"
"fmt"
"log"
"net"
"strings"
"time"
"github.com/miekg/dns"
)
type preCheckDNSFunc func(fqdn, value string) (bool, error)
var preCheckDNS preCheckDNSFunc = checkDNSPropagation
var recursiveNameserver = "google-public-dns-a.google.com"
// DNS01Record returns a DNS record which will fulfill the `dns-01` challenge
func DNS01Record(domain, keyAuth string) (fqdn string, value string, ttl int) {
keyAuthShaBytes := sha256.Sum256([]byte(keyAuth))
// base64URL encoding without padding
keyAuthSha := base64.URLEncoding.EncodeToString(keyAuthShaBytes[:sha256.Size])
value = strings.TrimRight(keyAuthSha, "=")
ttl = 120
fqdn = fmt.Sprintf("_acme-challenge.%s.", domain)
return
}
// dnsChallenge implements the dns-01 challenge according to ACME 7.5
type dnsChallenge struct {
jws *jws
validate validateFunc
provider ChallengeProvider
}
func (s *dnsChallenge) Solve(chlng challenge, domain string) error {
logf("[INFO][%s] acme: Trying to solve DNS-01", domain)
if s.provider == nil {
return errors.New("No DNS Provider configured")
}
// Generate the Key Authorization for the challenge
keyAuth, err := getKeyAuthorization(chlng.Token, &s.jws.privKey.PublicKey)
if err != nil {
return err
}
err = s.provider.Present(domain, chlng.Token, keyAuth)
if err != nil {
return fmt.Errorf("Error presenting token %s", err)
}
defer func() {
err := s.provider.CleanUp(domain, chlng.Token, keyAuth)
if err != nil {
log.Printf("Error cleaning up %s %v ", domain, err)
}
}()
fqdn, value, _ := DNS01Record(domain, keyAuth)
logf("[INFO][%s] Checking DNS record propagation...", domain)
err = waitFor(30, 2, func() (bool, error) {
return preCheckDNS(fqdn, value)
})
if err != nil {
return err
}
return s.validate(s.jws, domain, chlng.URI, challenge{Resource: "challenge", Type: chlng.Type, Token: chlng.Token, KeyAuthorization: keyAuth})
}
// checkDNSPropagation checks if the expected TXT record has been propagated to all authoritative nameservers.
func checkDNSPropagation(fqdn, value string) (bool, error) {
// Initial attempt to resolve at the recursive NS
r, err := dnsQuery(fqdn, dns.TypeTXT, recursiveNameserver, true)
if err != nil {
return false, err
}
if r.Rcode == dns.RcodeSuccess {
// If we see a CNAME here then use the alias
for _, rr := range r.Answer {
if cn, ok := rr.(*dns.CNAME); ok {
if cn.Hdr.Name == fqdn {
fqdn = cn.Target
break
}
}
}
}
authoritativeNss, err := lookupNameservers(fqdn)
if err != nil {
return false, err
}
return checkAuthoritativeNss(fqdn, value, authoritativeNss)
}
// checkAuthoritativeNss queries each of the given nameservers for the expected TXT record.
func checkAuthoritativeNss(fqdn, value string, nameservers []string) (bool, error) {
for _, ns := range nameservers {
r, err := dnsQuery(fqdn, dns.TypeTXT, ns, false)
if err != nil {
return false, err
}
if r.Rcode != dns.RcodeSuccess {
return false, fmt.Errorf("NS %s returned %s for %s", ns, dns.RcodeToString[r.Rcode], fqdn)
}
var found bool
for _, rr := range r.Answer {
if txt, ok := rr.(*dns.TXT); ok {
if strings.Join(txt.Txt, "") == value {
found = true
break
}
}
}
if !found {
return false, fmt.Errorf("NS %s did not return the expected TXT record", ns)
}
}
return true, nil
}
// dnsQuery sends a DNS query to the given nameserver.
func dnsQuery(fqdn string, rtype uint16, nameserver string, recursive bool) (in *dns.Msg, err error) {
m := new(dns.Msg)
m.SetQuestion(fqdn, rtype)
m.SetEdns0(4096, false)
if !recursive {
m.RecursionDesired = false
}
in, err = dns.Exchange(m, net.JoinHostPort(nameserver, "53"))
if err == dns.ErrTruncated {
tcp := &dns.Client{Net: "tcp"}
in, _, err = tcp.Exchange(m, nameserver)
}
return
}
// lookupNameservers returns the authoritative nameservers for the given fqdn.
func lookupNameservers(fqdn string) ([]string, error) {
var authoritativeNss []string
r, err := dnsQuery(fqdn, dns.TypeNS, recursiveNameserver, true)
if err != nil {
return nil, err
}
for _, rr := range r.Answer {
if ns, ok := rr.(*dns.NS); ok {
authoritativeNss = append(authoritativeNss, strings.ToLower(ns.Ns))
}
}
if len(authoritativeNss) > 0 {
return authoritativeNss, nil
}
// Strip of the left most label to get the parent domain.
offset, _ := dns.NextLabel(fqdn, 0)
next := fqdn[offset:]
if dns.CountLabel(next) < 2 {
return nil, fmt.Errorf("Could not determine authoritative nameservers")
}
return lookupNameservers(next)
}
// toFqdn converts the name into a fqdn appending a trailing dot.
func toFqdn(name string) string {
n := len(name)
if n == 0 || name[n-1] == '.' {
return name
}
return name + "."
}
// unFqdn converts the fqdn into a name removing the trailing dot.
func unFqdn(name string) string {
n := len(name)
if n != 0 && name[n-1] == '.' {
return name[:n-1]
}
return name
}
// waitFor polls the given function 'f', once every 'interval' seconds, up to 'timeout' seconds.
func waitFor(timeout, interval int, f func() (bool, error)) error {
var lastErr string
timeup := time.After(time.Duration(timeout) * time.Second)
for {
select {
case <-timeup:
return fmt.Errorf("Time limit exceeded. Last error: %s", lastErr)
default:
}
stop, err := f()
if stop {
return nil
}
if err != nil {
lastErr = err.Error()
}
time.Sleep(time.Duration(interval) * time.Second)
}
}