open-consul/connect/tls.go

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// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: MPL-2.0
package connect
import (
"crypto/tls"
"crypto/x509"
"errors"
"fmt"
"net"
"net/url"
"os"
"strings"
"sync"
"github.com/hashicorp/go-hclog"
"github.com/hashicorp/consul/agent/connect"
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"github.com/hashicorp/consul/api"
)
// parseLeafX509Cert will parse an X509 certificate
// from the TLS certificate and store the parsed
// value in the TLS certificate as the Leaf field.
func parseLeafX509Cert(leaf *tls.Certificate) error {
if leaf == nil {
// nothing to parse for nil cert
return nil
}
if leaf.Leaf != nil {
// leaf cert was already parsed
return nil
}
cert, err := x509.ParseCertificate(leaf.Certificate[0])
if err != nil {
return err
}
leaf.Leaf = cert
return nil
}
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// verifierFunc is a function that can accept rawCertificate bytes from a peer
// and verify them against a given tls.Config. It's called from the
// tls.Config.VerifyPeerCertificate hook.
//
// We don't pass verifiedChains since that is always nil in our usage.
// Implementations can use the roots provided in the cfg to verify the certs.
//
// The passed *tls.Config may have a nil VerifyPeerCertificates function but
// will have correct roots, leaf and other fields.
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type verifierFunc func(cfg *tls.Config, rawCerts [][]byte) error
// defaultTLSConfig returns the standard config with no peer verifier. It is
// insecure to use it as-is.
func defaultTLSConfig() *tls.Config {
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cfg := &tls.Config{
MinVersion: tls.VersionTLS12,
ClientAuth: tls.RequireAndVerifyClientCert,
// We don't have access to go internals that decide if AES hardware
// acceleration is available in order to prefer CHA CHA if not. So let's
// just always prefer AES for now. We can look into doing something uglier
// later like using an external lib for AES checking if it seems important.
// https://github.com/golang/go/blob/df91b8044dbe790c69c16058330f545be069cc1f/src/crypto/tls/common.go#L919:14
CipherSuites: []uint16{
tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
},
// We have to set this since otherwise Go will attempt to verify DNS names
// match DNS SAN/CN which we don't want. We hook up VerifyPeerCertificate to
// do our own path validation as well as Connect AuthZ.
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InsecureSkipVerify: true,
// Include h2 to allow connect http servers to automatically support http2.
// See: https://github.com/golang/go/blob/917c33fe8672116b04848cf11545296789cafd3b/src/net/http/server.go#L2724-L2731
NextProtos: []string{"h2"},
}
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return cfg
}
// devTLSConfigFromFiles returns a default TLS Config but with certs and CAs
// based on local files for dev. No verification is setup.
func devTLSConfigFromFiles(caFile, certFile,
keyFile string) (*tls.Config, error) {
roots := x509.NewCertPool()
bs, err := os.ReadFile(caFile)
if err != nil {
return nil, err
}
roots.AppendCertsFromPEM(bs)
cert, err := tls.LoadX509KeyPair(certFile, keyFile)
if err != nil {
return nil, err
}
cfg := defaultTLSConfig()
cfg.Certificates = []tls.Certificate{cert}
cfg.RootCAs = roots
cfg.ClientCAs = roots
return cfg, nil
}
// CertURIFromConn is a helper to extract the service identifier URI from a
// net.Conn. If the net.Conn is not a *tls.Conn then an error is always
// returned. If the *tls.Conn didn't present a valid connect certificate, or is
// not yet past the handshake, an error is returned.
func CertURIFromConn(conn net.Conn) (connect.CertURI, error) {
tc, ok := conn.(*tls.Conn)
if !ok {
return nil, fmt.Errorf("invalid non-TLS connect client")
}
gotURI, err := extractCertURI(tc.ConnectionState().PeerCertificates)
if err != nil {
return nil, err
}
return connect.ParseCertURI(gotURI)
}
// extractCertURI returns the first URI SAN from the leaf certificate presented
// in the slice. The slice is expected to be the passed from
// tls.Conn.ConnectionState().PeerCertificates and requires that the leaf has at
// least one URI and the first URI is the correct one to use.
func extractCertURI(certs []*x509.Certificate) (*url.URL, error) {
if len(certs) < 1 {
return nil, errors.New("no peer certificate presented")
}
// Only check the first cert assuming this is the only leaf. It's not clear if
// services might ever legitimately present multiple leaf certificates or if
// the slice is just to allow presenting the whole chain of intermediates.
cert := certs[0]
// Our certs will only ever have a single URI for now so only check that
if len(cert.URIs) < 1 {
return nil, errors.New("peer certificate invalid")
}
return cert.URIs[0], nil
}
// verifyServerCertMatchesURI is used on tls connections dialed to a connect
// server to ensure that the certificate it presented has the correct identity.
func verifyServerCertMatchesURI(certs []*x509.Certificate, expected connect.CertURI) error {
expectedStr := expected.URI().String()
gotURI, err := extractCertURI(certs)
if err != nil {
return errors.New("peer certificate mismatch")
}
// Override the hostname since we rely on x509 constraints to limit ability to
// spoof the trust domain if needed (i.e. because a root is shared with other
// PKI or Consul clusters). This allows for seamless migrations between trust
// domains.
expectURI := expected.URI()
expectURI.Host = gotURI.Host
if strings.EqualFold(gotURI.String(), expectURI.String()) {
return nil
}
return fmt.Errorf("peer certificate mismatch got %s, want %s",
gotURI.String(), expectedStr)
}
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// newServerSideVerifier returns a verifierFunc that wraps the provided
// api.Client to verify the TLS chain and perform AuthZ for the server end of
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// the connection. The service name provided is used as the target service name
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// for the Authorization.
func newServerSideVerifier(logger hclog.Logger, client *api.Client, serviceName string) verifierFunc {
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return func(tlsCfg *tls.Config, rawCerts [][]byte) error {
leaf, err := verifyChain(tlsCfg, rawCerts, false)
if err != nil {
logger.Error("failed TLS verification", "error", err)
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return err
}
// Check leaf is a cert we understand
if len(leaf.URIs) < 1 {
logger.Error("invalid leaf certificate: no URIs set")
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return errors.New("connect: invalid leaf certificate")
}
certURI, err := connect.ParseCertURI(leaf.URIs[0])
if err != nil {
logger.Error("invalid leaf certificate URI", "error", err)
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return errors.New("connect: invalid leaf certificate URI")
}
// No AuthZ if there is no client.
if client == nil {
logger.Info("nil client provided")
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return nil
}
// Perform AuthZ
req := &api.AgentAuthorizeParams{
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Target: serviceName,
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ClientCertURI: certURI.URI().String(),
ClientCertSerial: connect.EncodeSerialNumber(leaf.SerialNumber),
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}
resp, err := client.Agent().ConnectAuthorize(req)
if err != nil {
logger.Error("authz call failed", "error", err)
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return errors.New("connect: authz call failed: " + err.Error())
}
if !resp.Authorized {
logger.Error("authz call denied", "reason", resp.Reason)
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return errors.New("connect: authz denied: " + resp.Reason)
}
return nil
}
}
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// clientSideVerifier is a verifierFunc that performs verification of certificates
// on the client end of the connection. For now it is just basic TLS
// verification since the identity check needs additional state and becomes
// clunky to customize the callback for every outgoing request. That is done
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// within Service.Dial for now.
func clientSideVerifier(tlsCfg *tls.Config, rawCerts [][]byte) error {
_, err := verifyChain(tlsCfg, rawCerts, true)
return err
}
// verifyChain performs standard TLS verification without enforcing remote
// hostname matching.
func verifyChain(tlsCfg *tls.Config, rawCerts [][]byte, client bool) (*x509.Certificate, error) {
// Fetch leaf and intermediates. This is based on code form tls handshake.
if len(rawCerts) < 1 {
return nil, errors.New("tls: no certificates from peer")
}
certs := make([]*x509.Certificate, len(rawCerts))
for i, asn1Data := range rawCerts {
cert, err := x509.ParseCertificate(asn1Data)
if err != nil {
return nil, errors.New("tls: failed to parse certificate from peer: " + err.Error())
}
certs[i] = cert
}
cas := tlsCfg.RootCAs
if client {
cas = tlsCfg.ClientCAs
}
opts := x509.VerifyOptions{
Roots: cas,
Intermediates: x509.NewCertPool(),
}
if !client {
// Server side only sets KeyUsages in tls. This defaults to ServerAuth in
// x509 lib. See
// https://github.com/golang/go/blob/ee7dd810f9ca4e63ecfc1d3044869591783b8b74/src/crypto/x509/verify.go#L866-L868
opts.KeyUsages = []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth}
}
// All but the first cert are intermediates
for _, cert := range certs[1:] {
opts.Intermediates.AddCert(cert)
}
_, err := certs[0].Verify(opts)
return certs[0], err
}
// dynamicTLSConfig represents the state for returning a tls.Config that can
// have root and leaf certificates updated dynamically with all existing clients
// and servers automatically picking up the changes. It requires initializing
// with a valid base config from which all the non-certificate and verification
// params are used. The base config passed should not be modified externally as
// it is assumed to be serialized by the embedded mutex.
type dynamicTLSConfig struct {
base *tls.Config
sync.RWMutex
leaf *tls.Certificate
roots *x509.CertPool
// readyCh is closed when the config first gets both leaf and roots set.
// Watchers can wait on this via ReadyWait.
readyCh chan struct{}
}
type tlsCfgUpdate struct {
ch chan struct{}
next *tlsCfgUpdate
}
// newDynamicTLSConfig returns a dynamicTLSConfig constructed from base.
// base.Certificates[0] is used as the initial leaf and base.RootCAs is used as
// the initial roots.
func newDynamicTLSConfig(base *tls.Config, logger hclog.Logger) *dynamicTLSConfig {
cfg := &dynamicTLSConfig{
base: base,
}
if len(base.Certificates) > 0 {
cfg.leaf = &base.Certificates[0]
// If this does error then future calls to Ready will fail
// It is better to handle not-Ready rather than failing
if err := parseLeafX509Cert(cfg.leaf); err != nil && logger != nil {
logger.Error("error parsing configured leaf certificate", "error", err)
}
}
if base.RootCAs != nil {
cfg.roots = base.RootCAs
}
if !cfg.Ready() {
cfg.readyCh = make(chan struct{})
}
return cfg
}
// Get fetches the lastest tls.Config with all the hooks attached to keep it
// loading the most recent roots and certs even after future changes to cfg.
//
// The verifierFunc passed will be attached to the config returned such that it
// runs with the _latest_ config object returned passed to it. That means that a
// client can use this config for a long time and will still verify against the
// latest roots even though the roots in the struct is has can't change.
func (cfg *dynamicTLSConfig) Get(v verifierFunc) *tls.Config {
cfg.RLock()
defer cfg.RUnlock()
copy := cfg.base.Clone()
copy.RootCAs = cfg.roots
copy.ClientCAs = cfg.roots
if v != nil {
copy.VerifyPeerCertificate = func(rawCerts [][]byte, chains [][]*x509.Certificate) error {
return v(cfg.Get(nil), rawCerts)
}
}
copy.GetCertificate = func(_ *tls.ClientHelloInfo) (*tls.Certificate, error) {
leaf := cfg.Leaf()
if leaf == nil {
return nil, errors.New("tls: no certificates configured")
}
return leaf, nil
}
copy.GetClientCertificate = func(_ *tls.CertificateRequestInfo) (*tls.Certificate, error) {
leaf := cfg.Leaf()
if leaf == nil {
return nil, errors.New("tls: no certificates configured")
}
return leaf, nil
}
copy.GetConfigForClient = func(*tls.ClientHelloInfo) (*tls.Config, error) {
return cfg.Get(v), nil
}
return copy
}
// SetRoots sets new roots.
func (cfg *dynamicTLSConfig) SetRoots(roots *x509.CertPool) error {
cfg.Lock()
defer cfg.Unlock()
cfg.roots = roots
cfg.notify()
return nil
}
// SetLeaf sets a new leaf.
func (cfg *dynamicTLSConfig) SetLeaf(leaf *tls.Certificate) error {
cfg.Lock()
defer cfg.Unlock()
if err := parseLeafX509Cert(leaf); err != nil {
return err
}
cfg.leaf = leaf
cfg.notify()
return nil
}
// notify is called under lock during an update to check if we are now ready.
func (cfg *dynamicTLSConfig) notify() {
if cfg.readyCh != nil && cfg.leaf != nil && cfg.roots != nil && cfg.leaf.Leaf != nil {
close(cfg.readyCh)
cfg.readyCh = nil
}
}
func (cfg *dynamicTLSConfig) VerifyLeafWithRoots() error {
cfg.RLock()
defer cfg.RUnlock()
if cfg.roots == nil {
return fmt.Errorf("No roots are set")
} else if cfg.leaf == nil {
return fmt.Errorf("No leaf certificate is set")
} else if cfg.leaf.Leaf == nil {
return fmt.Errorf("Leaf certificate has not been parsed")
}
_, err := cfg.leaf.Leaf.Verify(x509.VerifyOptions{Roots: cfg.roots})
return err
}
// Roots returns the current CA root CertPool.
func (cfg *dynamicTLSConfig) Roots() *x509.CertPool {
cfg.RLock()
defer cfg.RUnlock()
return cfg.roots
}
// Leaf returns the current Leaf certificate.
func (cfg *dynamicTLSConfig) Leaf() *tls.Certificate {
cfg.RLock()
defer cfg.RUnlock()
return cfg.leaf
}
// Ready returns whether or not both roots and a leaf certificate are
// configured. If both are non-nil, they are assumed to be valid and usable.
func (cfg *dynamicTLSConfig) Ready() bool {
// not locking because VerifyLeafWithRoots will do that
return cfg.VerifyLeafWithRoots() == nil
}
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// ReadyWait returns a chan that is closed when the the Service becomes ready
// for use for the first time. Note that if the Service is ready when it is
// called it returns a nil chan. Ready means that it has root and leaf
// certificates configured but not that the combination is valid nor that
// the current time is within the validity window of the certificate. The
// service may subsequently stop being "ready" if it's certificates expire
// or are revoked and an error prevents new ones from being loaded but this
// method will not stop returning a nil chan in that case. It is only useful
// for initial startup. For ongoing health Ready() should be used.
func (cfg *dynamicTLSConfig) ReadyWait() <-chan struct{} {
cfg.RLock()
defer cfg.RUnlock()
return cfg.readyCh
}