package acme import ( "crypto/sha256" "encoding/base64" "errors" "fmt" "net" "strings" "time" "github.com/miekg/dns" "github.com/xenolf/lego/log" ) type preCheckDNSFunc func(fqdn, value string) (bool, error) var ( // PreCheckDNS checks DNS propagation before notifying ACME that // the DNS challenge is ready. PreCheckDNS preCheckDNSFunc = checkDNSPropagation fqdnToZone = map[string]string{} ) const defaultResolvConf = "/etc/resolv.conf" const ( // DefaultPropagationTimeout default propagation timeout DefaultPropagationTimeout = 60 * time.Second // DefaultPollingInterval default polling interval DefaultPollingInterval = 2 * time.Second // DefaultTTL default TTL DefaultTTL = 120 ) var defaultNameservers = []string{ "google-public-dns-a.google.com:53", "google-public-dns-b.google.com:53", } // RecursiveNameservers are used to pre-check DNS propagation var RecursiveNameservers = getNameservers(defaultResolvConf, defaultNameservers) // DNSTimeout is used to override the default DNS timeout of 10 seconds. var DNSTimeout = 10 * time.Second // getNameservers attempts to get systems nameservers before falling back to the defaults func getNameservers(path string, defaults []string) []string { config, err := dns.ClientConfigFromFile(path) if err != nil || len(config.Servers) == 0 { return defaults } systemNameservers := []string{} for _, server := range config.Servers { // ensure all servers have a port number if _, _, err := net.SplitHostPort(server); err != nil { systemNameservers = append(systemNameservers, net.JoinHostPort(server, "53")) } else { systemNameservers = append(systemNameservers, server) } } return systemNameservers } // 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 value = base64.RawURLEncoding.EncodeToString(keyAuthShaBytes[:sha256.Size]) ttl = DefaultTTL 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 } // PreSolve just submits the txt record to the dns provider. It does not validate record propagation, or // do anything at all with the acme server. func (s *dnsChallenge) PreSolve(chlng challenge, domain string) error { log.Infof("[%s] acme: Preparing 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) if err != nil { return err } err = s.provider.Present(domain, chlng.Token, keyAuth) if err != nil { return fmt.Errorf("error presenting token: %s", err) } return nil } func (s *dnsChallenge) Solve(chlng challenge, domain string) error { log.Infof("[%s] acme: Trying to solve DNS-01", domain) // Generate the Key Authorization for the challenge keyAuth, err := getKeyAuthorization(chlng.Token, s.jws.privKey) if err != nil { return err } fqdn, value, _ := DNS01Record(domain, keyAuth) log.Infof("[%s] Checking DNS record propagation using %+v", domain, RecursiveNameservers) var timeout, interval time.Duration switch provider := s.provider.(type) { case ChallengeProviderTimeout: timeout, interval = provider.Timeout() default: timeout, interval = DefaultPropagationTimeout, DefaultPollingInterval } err = WaitFor(timeout, interval, func() (bool, error) { return PreCheckDNS(fqdn, value) }) if err != nil { return err } return s.validate(s.jws, domain, chlng.URL, challenge{Type: chlng.Type, Token: chlng.Token, KeyAuthorization: keyAuth}) } // CleanUp cleans the challenge func (s *dnsChallenge) CleanUp(chlng challenge, domain string) error { keyAuth, err := getKeyAuthorization(chlng.Token, s.jws.privKey) if err != nil { return err } return s.provider.CleanUp(domain, chlng.Token, 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, RecursiveNameservers, 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, []string{net.JoinHostPort(ns, "53")}, 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 will query a nameserver, iterating through the supplied servers as it retries // The nameserver should include a port, to facilitate testing where we talk to a mock dns server. func dnsQuery(fqdn string, rtype uint16, nameservers []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 } // Will retry the request based on the number of servers (n+1) for i := 1; i <= len(nameservers)+1; i++ { ns := nameservers[i%len(nameservers)] udp := &dns.Client{Net: "udp", Timeout: DNSTimeout} in, _, err = udp.Exchange(m, ns) if err == dns.ErrTruncated { tcp := &dns.Client{Net: "tcp", Timeout: DNSTimeout} // If the TCP request succeeds, the err will reset to nil in, _, err = tcp.Exchange(m, ns) } if err == nil { break } } return } // lookupNameservers returns the authoritative nameservers for the given fqdn. func lookupNameservers(fqdn string) ([]string, error) { var authoritativeNss []string zone, err := FindZoneByFqdn(fqdn, RecursiveNameservers) if err != nil { return nil, fmt.Errorf("could not determine the zone: %v", err) } r, err := dnsQuery(zone, dns.TypeNS, RecursiveNameservers, 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 } return nil, fmt.Errorf("could not determine authoritative nameservers") } // FindZoneByFqdn determines the zone apex for the given fqdn by recursing up the // domain labels until the nameserver returns a SOA record in the answer section. func FindZoneByFqdn(fqdn string, nameservers []string) (string, error) { // Do we have it cached? if zone, ok := fqdnToZone[fqdn]; ok { return zone, nil } labelIndexes := dns.Split(fqdn) for _, index := range labelIndexes { domain := fqdn[index:] in, err := dnsQuery(domain, dns.TypeSOA, nameservers, true) if err != nil { return "", err } // Any response code other than NOERROR and NXDOMAIN is treated as error if in.Rcode != dns.RcodeNameError && in.Rcode != dns.RcodeSuccess { return "", fmt.Errorf("unexpected response code '%s' for %s", dns.RcodeToString[in.Rcode], domain) } // Check if we got a SOA RR in the answer section if in.Rcode == dns.RcodeSuccess { // CNAME records cannot/should not exist at the root of a zone. // So we skip a domain when a CNAME is found. if dnsMsgContainsCNAME(in) { continue } for _, ans := range in.Answer { if soa, ok := ans.(*dns.SOA); ok { zone := soa.Hdr.Name fqdnToZone[fqdn] = zone return zone, nil } } } } return "", fmt.Errorf("could not find the start of authority") } // dnsMsgContainsCNAME checks for a CNAME answer in msg func dnsMsgContainsCNAME(msg *dns.Msg) bool { for _, ans := range msg.Answer { if _, ok := ans.(*dns.CNAME); ok { return true } } return false } // ClearFqdnCache clears the cache of fqdn to zone mappings. Primarily used in testing. func ClearFqdnCache() { fqdnToZone = map[string]string{} } // 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 }