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// Copyright 2015 Light Code Labs, LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package caddytls
import (
"crypto/tls"
"errors"
"fmt"
"log"
"net/http"
"net/url"
"strings"
"sync"
"sync/atomic"
"time"
"github.com/mholt/caddy/telemetry"
)
// configGroup is a type that keys configs by their hostname
// (hostnames can have wildcard characters; use the getConfig
// method to get a config by matching its hostname).
type configGroup map[string]*Config
// getConfig gets the config by the first key match for name.
// In other words, "sub.foo.bar" will get the config for "*.foo.bar"
// if that is the closest match. If no match is found, the first
// (random) config will be loaded, which will defer any TLS alerts
// to the certificate validation (this may or may not be ideal;
// let's talk about it if this becomes problematic).
//
// This function follows nearly the same logic to lookup
// a hostname as the getCertificate function uses.
func (cg configGroup) getConfig(name string) *Config {
name = strings.ToLower(name)
// exact match? great, let's use it
if config, ok := cg[name]; ok {
return config
}
// try replacing labels in the name with wildcards until we get a match
labels := strings.Split(name, ".")
for i := range labels {
labels[i] = "*"
candidate := strings.Join(labels, ".")
if config, ok := cg[candidate]; ok {
return config
}
}
// try a config that serves all names (the above
// loop doesn't try empty string; for hosts defined
// with only a port, for instance, like ":443") -
// also known as the default config
if config, ok := cg[""]; ok {
return config
}
return nil
}
// GetConfigForClient gets a TLS configuration satisfying clientHello.
// In getting the configuration, it abides the rules and settings
// defined in the Config that matches clientHello.ServerName. If no
// tls.Config is set on the matching Config, a nil value is returned.
//
// This method is safe for use as a tls.Config.GetConfigForClient callback.
func (cg configGroup) GetConfigForClient(clientHello *tls.ClientHelloInfo) (*tls.Config, error) {
config := cg.getConfig(clientHello.ServerName)
if config != nil {
return config.tlsConfig, nil
}
return nil, nil
}
// GetCertificate gets a certificate to satisfy clientHello. In getting
// the certificate, it abides the rules and settings defined in the
// Config that matches clientHello.ServerName. It first checks the in-
// memory cache, then, if the config enables "OnDemand", it accesses
// disk, then accesses the network if it must obtain a new certificate
// via ACME.
//
// This method is safe for use as a tls.Config.GetCertificate callback.
func (cfg *Config) GetCertificate(clientHello *tls.ClientHelloInfo) (*tls.Certificate, error) {
if ClientHelloTelemetry && len(clientHello.SupportedVersions) > 0 {
// If no other plugin (such as the HTTP server type) is implementing ClientHello telemetry, we do it.
// NOTE: The values in the Go standard lib's ClientHelloInfo aren't guaranteed to be in order.
info := ClientHelloInfo{
Version: clientHello.SupportedVersions[0], // report the highest
CipherSuites: clientHello.CipherSuites,
ExtensionsUnknown: true, // no extension info... :(
CompressionMethodsUnknown: true, // no compression methods... :(
Curves: clientHello.SupportedCurves,
Points: clientHello.SupportedPoints,
// We also have, but do not yet use: SignatureSchemes, ServerName, and SupportedProtos (ALPN)
// because the standard lib parses some extensions, but our MITM detector generally doesn't.
}
go telemetry.SetNested("tls_client_hello", info.Key(), info)
}
// get the certificate and serve it up
cert, err := cfg.getCertDuringHandshake(strings.ToLower(clientHello.ServerName), true, true)
if err == nil {
go telemetry.Increment("tls_handshake_count") // TODO: This is a "best guess" for now, we need something listener-level
}
return &cert.Certificate, err
}
// getCertificate gets a certificate that matches name (a server name)
// from the in-memory cache, according to the lookup table associated with
// cfg. The lookup then points to a certificate in the Instance certificate
// cache.
//
// If there is no exact match for name, it will be checked against names of
// the form '*.example.com' (wildcard certificates) according to RFC 6125.
// If a match is found, matched will be true. If no matches are found, matched
// will be false and a "default" certificate will be returned with defaulted
// set to true. If defaulted is false, then no certificates were available.
//
// The logic in this function is adapted from the Go standard library,
// which is by the Go Authors.
//
// This function is safe for concurrent use.
func (cfg *Config) getCertificate(name string) (cert Certificate, matched, defaulted bool) {
var certKey string
var ok bool
// Not going to trim trailing dots here since RFC 3546 says,
// "The hostname is represented ... without a trailing dot."
// Just normalize to lowercase.
name = strings.ToLower(name)
cfg.certCache.RLock()
defer cfg.certCache.RUnlock()
// exact match? great, let's use it
if certKey, ok = cfg.Certificates[name]; ok {
cert = cfg.certCache.cache[certKey]
matched = true
return
}
// try replacing labels in the name with wildcards until we get a match
labels := strings.Split(name, ".")
for i := range labels {
labels[i] = "*"
candidate := strings.Join(labels, ".")
if certKey, ok = cfg.Certificates[candidate]; ok {
cert = cfg.certCache.cache[certKey]
matched = true
return
}
}
// check the certCache directly to see if the SNI name is
// already the key of the certificate it wants! this is vital
// for supporting the TLS-SNI challenge, since the tlsSNISolver
// just puts the temporary certificate in the instance cache,
// with no regard for configs; this also means that the SNI
// can contain the hash of a specific cert (chain) it wants
// and we will still be able to serve it up
// (this behavior, by the way, could be controversial as to
// whether it complies with RFC 6066 about SNI, but I think
// it does soooo...)
// NOTE/TODO: TLS-SNI challenge is changing, as of Jan. 2018
// but what will be different, if it ever returns, is unclear
if directCert, ok := cfg.certCache.cache[name]; ok {
cert = directCert
matched = true
return
}
// if nothing matches, use a "default" certificate
// (See issues 2035 and 1303; any change to this behavior
// must account for hosts defined like ":443" or
// "0.0.0.0:443" where the hostname is empty or a catch-all
// IP or something.)
if certKey, ok := cfg.Certificates[""]; ok {
cert = cfg.certCache.cache[certKey]
defaulted = true
return
}
return
}
// getCertDuringHandshake will get a certificate for name. It first tries
// the in-memory cache. If no certificate for name is in the cache, the
// config most closely corresponding to name will be loaded. If that config
// allows it (OnDemand==true) and if loadIfNecessary == true, it goes to disk
// to load it into the cache and serve it. If it's not on disk and if
// obtainIfNecessary == true, the certificate will be obtained from the CA,
// cached, and served. If obtainIfNecessary is true, then loadIfNecessary
// must also be set to true. An error will be returned if and only if no
// certificate is available.
//
// This function is safe for concurrent use.
func (cfg *Config) getCertDuringHandshake(name string, loadIfNecessary, obtainIfNecessary bool) (Certificate, error) {
// First check our in-memory cache to see if we've already loaded it
cert, matched, defaulted := cfg.getCertificate(name)
if matched {
return cert, nil
}
// If OnDemand is enabled, then we might be able to load or
// obtain a needed certificate
if cfg.OnDemand && loadIfNecessary {
// Then check to see if we have one on disk
loadedCert, err := cfg.CacheManagedCertificate(name)
if err == nil {
loadedCert, err = cfg.handshakeMaintenance(name, loadedCert)
if err != nil {
log.Printf("[ERROR] Maintaining newly-loaded certificate for %s: %v", name, err)
}
return loadedCert, nil
}
if obtainIfNecessary {
// By this point, we need to ask the CA for a certificate
name = strings.ToLower(name)
// Make sure the certificate should be obtained based on config
err := cfg.checkIfCertShouldBeObtained(name)
if err != nil {
return Certificate{}, err
}
// Name has to qualify for a certificate
if !HostQualifies(name) {
return cert, errors.New("hostname '" + name + "' does not qualify for certificate")
}
// Obtain certificate from the CA
return cfg.obtainOnDemandCertificate(name)
}
}
// Fall back to the default certificate if there is one
if defaulted {
return cert, nil
}
return Certificate{}, fmt.Errorf("no certificate available for %s", name)
}
// checkIfCertShouldBeObtained checks to see if an on-demand tls certificate
// should be obtained for a given domain based upon the config settings. If
// a non-nil error is returned, do not issue a new certificate for name.
func (cfg *Config) checkIfCertShouldBeObtained(name string) error {
// If the "ask" URL is defined in the config, use to determine if a
// cert should obtained
if cfg.OnDemandState.AskURL != nil {
return cfg.checkURLForObtainingNewCerts(name)
}
// Otherwise use the limit defined by the "max_certs" setting
return cfg.checkLimitsForObtainingNewCerts(name)
}
func (cfg *Config) checkURLForObtainingNewCerts(name string) error {
client := http.Client{
Timeout: 10 * time.Second,
CheckRedirect: func(req *http.Request, via []*http.Request) error {
return errors.New("following http redirects is not allowed")
},
}
// Copy the URL from the config in order to modify it for this request
askURL := new(url.URL)
*askURL = *cfg.OnDemandState.AskURL
query := askURL.Query()
query.Set("domain", name)
askURL.RawQuery = query.Encode()
resp, err := client.Get(askURL.String())
if err != nil {
return fmt.Errorf("error checking %v to deterine if certificate for hostname '%s' should be allowed: %v", cfg.OnDemandState.AskURL, name, err)
}
defer resp.Body.Close()
if resp.StatusCode < 200 || resp.StatusCode > 299 {
return fmt.Errorf("certificate for hostname '%s' not allowed, non-2xx status code %d returned from %v", name, resp.StatusCode, cfg.OnDemandState.AskURL)
}
return nil
}
// checkLimitsForObtainingNewCerts checks to see if name can be issued right
// now according the maximum count defined in the configuration. If a non-nil
// error is returned, do not issue a new certificate for name.
func (cfg *Config) checkLimitsForObtainingNewCerts(name string) error {
// User can set hard limit for number of certs for the process to issue
if cfg.OnDemandState.MaxObtain > 0 &&
atomic.LoadInt32(&cfg.OnDemandState.ObtainedCount) >= cfg.OnDemandState.MaxObtain {
return fmt.Errorf("%s: maximum certificates issued (%d)", name, cfg.OnDemandState.MaxObtain)
}
// Make sure name hasn't failed a challenge recently
failedIssuanceMu.RLock()
when, ok := failedIssuance[name]
failedIssuanceMu.RUnlock()
if ok {
return fmt.Errorf("%s: throttled; refusing to issue cert since last attempt on %s failed", name, when.String())
}
// Make sure, if we've issued a few certificates already, that we haven't
// issued any recently
lastIssueTimeMu.Lock()
since := time.Since(lastIssueTime)
lastIssueTimeMu.Unlock()
if atomic.LoadInt32(&cfg.OnDemandState.ObtainedCount) >= 10 && since < 10*time.Minute {
return fmt.Errorf("%s: throttled; last certificate was obtained %v ago", name, since)
}
// Good to go 👍
return nil
}
// obtainOnDemandCertificate obtains a certificate for name for the given
// name. If another goroutine has already started obtaining a cert for
// name, it will wait and use what the other goroutine obtained.
//
// This function is safe for use by multiple concurrent goroutines.
func (cfg *Config) obtainOnDemandCertificate(name string) (Certificate, error) {
// We must protect this process from happening concurrently, so synchronize.
obtainCertWaitChansMu.Lock()
wait, ok := obtainCertWaitChans[name]
if ok {
// lucky us -- another goroutine is already obtaining the certificate.
// wait for it to finish obtaining the cert and then we'll use it.
obtainCertWaitChansMu.Unlock()
<-wait
return cfg.getCertDuringHandshake(name, true, false)
}
// looks like it's up to us to do all the work and obtain the cert.
// make a chan others can wait on if needed
wait = make(chan struct{})
obtainCertWaitChans[name] = wait
obtainCertWaitChansMu.Unlock()
// obtain the certificate
log.Printf("[INFO] Obtaining new certificate for %s", name)
err := cfg.ObtainCert(name, false)
// immediately unblock anyone waiting for it; doing this in
// a defer would risk deadlock because of the recursive call
// to getCertDuringHandshake below when we return!
obtainCertWaitChansMu.Lock()
close(wait)
delete(obtainCertWaitChans, name)
obtainCertWaitChansMu.Unlock()
if err != nil {
// Failed to solve challenge, so don't allow another on-demand
// issue for this name to be attempted for a little while.
failedIssuanceMu.Lock()
failedIssuance[name] = time.Now()
go func(name string) {
time.Sleep(5 * time.Minute)
failedIssuanceMu.Lock()
delete(failedIssuance, name)
failedIssuanceMu.Unlock()
}(name)
failedIssuanceMu.Unlock()
return Certificate{}, err
}
// Success - update counters and stuff
atomic.AddInt32(&cfg.OnDemandState.ObtainedCount, 1)
lastIssueTimeMu.Lock()
lastIssueTime = time.Now()
lastIssueTimeMu.Unlock()
// certificate is already on disk; now just start over to load it and serve it
return cfg.getCertDuringHandshake(name, true, false)
}
// handshakeMaintenance performs a check on cert for expiration and OCSP
// validity.
//
// This function is safe for use by multiple concurrent goroutines.
func (cfg *Config) handshakeMaintenance(name string, cert Certificate) (Certificate, error) {
// Check cert expiration
timeLeft := cert.NotAfter.Sub(time.Now().UTC())
if timeLeft < RenewDurationBefore {
log.Printf("[INFO] Certificate for %v expires in %v; attempting renewal", cert.Names, timeLeft)
return cfg.renewDynamicCertificate(name, cert)
}
// Check OCSP staple validity
if cert.OCSP != nil {
refreshTime := cert.OCSP.ThisUpdate.Add(cert.OCSP.NextUpdate.Sub(cert.OCSP.ThisUpdate) / 2)
if time.Now().After(refreshTime) {
err := stapleOCSP(&cert, nil)
if err != nil {
// An error with OCSP stapling is not the end of the world, and in fact, is
// quite common considering not all certs have issuer URLs that support it.
log.Printf("[ERROR] Getting OCSP for %s: %v", name, err)
}
cfg.certCache.Lock()
cfg.certCache.cache[cert.Hash] = cert
cfg.certCache.Unlock()
}
}
return cert, nil
}
// renewDynamicCertificate renews the certificate for name using cfg. It returns the
// certificate to use and an error, if any. name should already be lower-cased before
// calling this function. name is the name obtained directly from the handshake's
// ClientHello.
//
// This function is safe for use by multiple concurrent goroutines.
func (cfg *Config) renewDynamicCertificate(name string, currentCert Certificate) (Certificate, error) {
obtainCertWaitChansMu.Lock()
wait, ok := obtainCertWaitChans[name]
if ok {
// lucky us -- another goroutine is already renewing the certificate.
// wait for it to finish, then we'll use the new one.
obtainCertWaitChansMu.Unlock()
<-wait
return cfg.getCertDuringHandshake(name, true, false)
}
// looks like it's up to us to do all the work and renew the cert
wait = make(chan struct{})
obtainCertWaitChans[name] = wait
obtainCertWaitChansMu.Unlock()
// renew and reload the certificate
log.Printf("[INFO] Renewing certificate for %s", name)
err := cfg.RenewCert(name, false)
if err == nil {
// even though the recursive nature of the dynamic cert loading
// would just call this function anyway, we do it here to
// make the replacement as atomic as possible.
newCert, err := currentCert.configs[0].CacheManagedCertificate(name)
if err != nil {
log.Printf("[ERROR] loading renewed certificate for %s: %v", name, err)
} else {
// replace the old certificate with the new one
err = cfg.certCache.replaceCertificate(currentCert, newCert)
if err != nil {
log.Printf("[ERROR] Replacing certificate for %s: %v", name, err)
}
}
}
// immediately unblock anyone waiting for it; doing this in
// a defer would risk deadlock because of the recursive call
// to getCertDuringHandshake below when we return!
obtainCertWaitChansMu.Lock()
close(wait)
delete(obtainCertWaitChans, name)
obtainCertWaitChansMu.Unlock()
if err != nil {
return Certificate{}, err
}
return cfg.getCertDuringHandshake(name, true, false)
}
// ClientHelloInfo is our own version of the standard lib's
// tls.ClientHelloInfo. As of May 2018, any fields populated
// by the Go standard library are not guaranteed to have their
// values in the original order as on the wire.
type ClientHelloInfo struct {
Version uint16 `json:"version,omitempty"`
CipherSuites []uint16 `json:"cipher_suites,omitempty"`
Extensions []uint16 `json:"extensions,omitempty"`
CompressionMethods []byte `json:"compression,omitempty"`
Curves []tls.CurveID `json:"curves,omitempty"`
Points []uint8 `json:"points,omitempty"`
// Whether a couple of fields are unknown; if not, the key will encode
// differently to reflect that, as opposed to being known empty values.
// (some fields may be unknown depending on what package is being used;
// i.e. the Go standard lib doesn't expose some things)
// (very important to NOT encode these to JSON)
ExtensionsUnknown bool `json:"-"`
CompressionMethodsUnknown bool `json:"-"`
}
// Key returns a standardized string form of the data in info,
// useful for identifying duplicates.
func (info ClientHelloInfo) Key() string {
extensions, compressionMethods := "?", "?"
if !info.ExtensionsUnknown {
extensions = fmt.Sprintf("%x", info.Extensions)
}
if !info.CompressionMethodsUnknown {
compressionMethods = fmt.Sprintf("%x", info.CompressionMethods)
}
return telemetry.FastHash([]byte(fmt.Sprintf("%x-%x-%s-%s-%x-%x",
info.Version, info.CipherSuites, extensions,
compressionMethods, info.Curves, info.Points)))
}
// obtainCertWaitChans is used to coordinate obtaining certs for each hostname.
var obtainCertWaitChans = make(map[string]chan struct{})
var obtainCertWaitChansMu sync.Mutex
// failedIssuance is a set of names that we recently failed to get a
// certificate for from the ACME CA. They are removed after some time.
// When a name is in this map, do not issue a certificate for it on-demand.
var failedIssuance = make(map[string]time.Time)
var failedIssuanceMu sync.RWMutex
// lastIssueTime records when we last obtained a certificate successfully.
// If this value is recent, do not make any on-demand certificate requests.
var lastIssueTime time.Time
var lastIssueTimeMu sync.Mutex
// ClientHelloTelemetry determines whether to report
// TLS ClientHellos to telemetry. Disable if doing
// it from a different package.
var ClientHelloTelemetry = true