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plugin.go
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plugin.go
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// +build go1.13
/*
*
* Copyright 2020 gRPC authors.
*
* 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 meshca provides an implementation of the Provider interface which
// communicates with MeshCA to get certificates signed.
package meshca
import (
"context"
"crypto"
"crypto/rand"
"crypto/rsa"
"crypto/tls"
"crypto/x509"
"encoding/pem"
"fmt"
"time"
durationpb "github.com/golang/protobuf/ptypes/duration"
"github.com/google/uuid"
"google.golang.org/grpc"
"google.golang.org/grpc/credentials/tls/certprovider"
meshgrpc "google.golang.org/grpc/credentials/tls/certprovider/meshca/internal/v1"
meshpb "google.golang.org/grpc/credentials/tls/certprovider/meshca/internal/v1"
"google.golang.org/grpc/internal/grpclog"
"google.golang.org/grpc/metadata"
)
// In requests sent to the MeshCA, we add a metadata header with this key and
// the value being the GCE zone in which the workload is running in.
const locationMetadataKey = "x-goog-request-params"
// For overriding from unit tests.
var newDistributorFunc = func() distributor { return certprovider.NewDistributor() }
// distributor wraps the methods on certprovider.Distributor which are used by
// the plugin. This is very useful in tests which need to know exactly when the
// plugin updates its key material.
type distributor interface {
KeyMaterial(ctx context.Context) (*certprovider.KeyMaterial, error)
Set(km *certprovider.KeyMaterial, err error)
Stop()
}
// providerPlugin is an implementation of the certprovider.Provider interface,
// which gets certificates signed by communicating with the MeshCA.
type providerPlugin struct {
distributor // Holds the key material.
cancel context.CancelFunc
cc *grpc.ClientConn // Connection to MeshCA server.
cfg *pluginConfig // Plugin configuration.
opts certprovider.BuildOptions // Key material options.
logger *grpclog.PrefixLogger // Plugin instance specific prefix.
backoff func(int) time.Duration // Exponential backoff.
doneFunc func() // Notify the builder when done.
}
// providerParams wraps params passed to the provider plugin at creation time.
type providerParams struct {
// This ClientConn to the MeshCA server is owned by the builder.
cc *grpc.ClientConn
cfg *pluginConfig
opts certprovider.BuildOptions
backoff func(int) time.Duration
doneFunc func()
}
func newProviderPlugin(params providerParams) *providerPlugin {
ctx, cancel := context.WithCancel(context.Background())
p := &providerPlugin{
cancel: cancel,
cc: params.cc,
cfg: params.cfg,
opts: params.opts,
backoff: params.backoff,
doneFunc: params.doneFunc,
distributor: newDistributorFunc(),
}
p.logger = prefixLogger((p))
p.logger.Infof("plugin created")
go p.run(ctx)
return p
}
func (p *providerPlugin) Close() {
p.logger.Infof("plugin closed")
p.Stop() // Stop the embedded distributor.
p.cancel()
p.doneFunc()
}
// run is a long running goroutine which periodically sends out CSRs to the
// MeshCA, and updates the underlying Distributor with the new key material.
func (p *providerPlugin) run(ctx context.Context) {
// We need to start fetching key material right away. The next attempt will
// be triggered by the timer firing.
for {
certValidity, err := p.updateKeyMaterial(ctx)
if err != nil {
return
}
// We request a certificate with the configured validity duration (which
// is usually twice as much as the grace period). But the server is free
// to return a certificate with whatever validity time it deems right.
refreshAfter := p.cfg.certGraceTime
if refreshAfter > certValidity {
// The default value of cert grace time is half that of the default
// cert validity time. So here, when we have to use a non-default
// cert life time, we will set the grace time again to half that of
// the validity time.
refreshAfter = certValidity / 2
}
timer := time.NewTimer(refreshAfter)
select {
case <-ctx.Done():
return
case <-timer.C:
}
}
}
// updateKeyMaterial generates a CSR and attempts to get it signed from the
// MeshCA. It retries with an exponential backoff till it succeeds or the
// deadline specified in ctx expires. Once it gets the CSR signed from the
// MeshCA, it updates the Distributor with the new key material.
//
// It returns the amount of time the new certificate is valid for.
func (p *providerPlugin) updateKeyMaterial(ctx context.Context) (time.Duration, error) {
client := meshgrpc.NewMeshCertificateServiceClient(p.cc)
retries := 0
for {
if ctx.Err() != nil {
return 0, ctx.Err()
}
if retries != 0 {
bi := p.backoff(retries)
p.logger.Warningf("Backing off for %s before attempting the next CreateCertificate() request", bi)
timer := time.NewTimer(bi)
select {
case <-timer.C:
case <-ctx.Done():
return 0, ctx.Err()
}
}
retries++
privKey, err := rsa.GenerateKey(rand.Reader, p.cfg.keySize)
if err != nil {
p.logger.Warningf("RSA key generation failed: %v", err)
continue
}
// We do not set any fields in the CSR (we use an empty
// x509.CertificateRequest as the template) because the MeshCA discards
// them anyways, and uses the workload identity from the access token
// that we present (as part of the STS call creds).
csrBytes, err := x509.CreateCertificateRequest(rand.Reader, &x509.CertificateRequest{}, crypto.PrivateKey(privKey))
if err != nil {
p.logger.Warningf("CSR creation failed: %v", err)
continue
}
csrPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE REQUEST", Bytes: csrBytes})
// Send out the CSR with a call timeout and location metadata, as
// specified in the plugin configuration.
req := &meshpb.MeshCertificateRequest{
RequestId: uuid.New().String(),
Csr: string(csrPEM),
Validity: &durationpb.Duration{Seconds: int64(p.cfg.certLifetime / time.Second)},
}
p.logger.Debugf("Sending CreateCertificate() request: %v", req)
callCtx, ctxCancel := context.WithTimeout(context.Background(), p.cfg.callTimeout)
callCtx = metadata.NewOutgoingContext(callCtx, metadata.Pairs(locationMetadataKey, p.cfg.location))
resp, err := client.CreateCertificate(callCtx, req)
if err != nil {
p.logger.Warningf("CreateCertificate request failed: %v", err)
ctxCancel()
continue
}
ctxCancel()
// The returned cert chain must contain more than one cert. Leaf cert is
// element '0', while root cert is element 'n', and the intermediate
// entries form the chain from the root to the leaf.
certChain := resp.GetCertChain()
if l := len(certChain); l <= 1 {
p.logger.Errorf("Received certificate chain contains %d certificates, need more than one", l)
continue
}
// We need to explicitly parse the PEM cert contents as an
// x509.Certificate to read the certificate validity period. We use this
// to decide when to refresh the cert. Even though the call to
// tls.X509KeyPair actually parses the PEM contents into an
// x509.Certificate, it does not store that in the `Leaf` field. See:
// https://golang.org/pkg/crypto/tls/#X509KeyPair.
identity, intermediates, roots, err := parseCertChain(certChain)
if err != nil {
p.logger.Errorf(err.Error())
continue
}
_, err = identity.Verify(x509.VerifyOptions{
Intermediates: intermediates,
Roots: roots,
})
if err != nil {
p.logger.Errorf("Certificate verification failed for return certChain: %v", err)
continue
}
key := x509.MarshalPKCS1PrivateKey(privKey)
keyPEM := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: key})
certPair, err := tls.X509KeyPair([]byte(certChain[0]), keyPEM)
if err != nil {
p.logger.Errorf("Failed to create x509 key pair: %v", err)
continue
}
// At this point, the received response has been deemed good.
retries = 0
// All certs signed by the MeshCA roll up to the same root. And treating
// the last element of the returned chain as the root is the only
// supported option to get the root certificate. So, we ignore the
// options specified in the call to Build(), which contain certificate
// name and whether the caller is interested in identity or root cert.
p.Set(&certprovider.KeyMaterial{Certs: []tls.Certificate{certPair}, Roots: roots}, nil)
return time.Until(identity.NotAfter), nil
}
}
// ParseCertChain parses the result returned by the MeshCA which consists of a
// list of PEM encoded certs. The first element in the list is the leaf or
// identity cert, while the last element is the root, and everything in between
// form the chain of trust.
//
// Caller needs to make sure that certChain has at least two elements.
func parseCertChain(certChain []string) (*x509.Certificate, *x509.CertPool, *x509.CertPool, error) {
identity, err := parseCert([]byte(certChain[0]))
if err != nil {
return nil, nil, nil, err
}
intermediates := x509.NewCertPool()
for _, cert := range certChain[1 : len(certChain)-1] {
i, err := parseCert([]byte(cert))
if err != nil {
return nil, nil, nil, err
}
intermediates.AddCert(i)
}
roots := x509.NewCertPool()
root, err := parseCert([]byte(certChain[len(certChain)-1]))
if err != nil {
return nil, nil, nil, err
}
roots.AddCert(root)
return identity, intermediates, roots, nil
}
func parseCert(certPEM []byte) (*x509.Certificate, error) {
block, _ := pem.Decode(certPEM)
if block == nil {
return nil, fmt.Errorf("failed to decode received PEM data: %v", certPEM)
}
return x509.ParseCertificate(block.Bytes)
}