metropolis/pkg/pki/certificate.go - monogon - Gitiles

 // Copyright 2020 The Monogon Project Authors.
 //
 // SPDX-License-Identifier: Apache-2.0
 //
 // 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 pki

 import (
 	"context"
 	"crypto/ed25519"
 	"crypto/x509"
 	"crypto/x509/pkix"
 	"encoding/pem"
 	"fmt"
 	"net"

 	"go.etcd.io/etcd/clientv3"

 	"source.monogon.dev/metropolis/pkg/fileargs"
 )

 // Namespace represents some path in etcd where certificate/CA data will be
 // stored. Creating a namespace via Namespaced then permits the consumer of
 // this library to start creating certificates within this namespace.
 type Namespace struct {
 	prefix string
 }

 // Namespaced creates a namespace for storing certificate data in etcd at a
 // given 'path' prefix.
 func Namespaced(prefix string) Namespace {
 	return Namespace{
 		prefix: prefix,
 	}
 }

 // Certificate is the promise of a Certificate being available to the caller.
 // In this case, Certificate refers to a pair of x509 certificate and
 // corresponding private key.  Certificates can be stored in etcd, and their
 // issuers might also be store on etcd. As such, this type's methods contain
 // references to an etcd KV client.  This Certificate type is agnostic to
 // usage, but mostly geared towards Kubernetes certificates.
 type Certificate struct {
 	namespace *Namespace

 	// issuer is the Issuer that will generate this certificate if one doesn't
 	// yet exist or etcd, or the requested certificate is volatile (not to be
 	// stored on etcd).
 	Issuer Issuer
 	// name is a unique key for storing the certificate in etcd. If empty,
 	// certificate is 'volatile', will not be stored on etcd, and every
 	// .Ensure() call will generate a new pair.
 	name string
 	// template is an x509 certificate definition that will be used to generate
 	// the certificate when issuing it.
 	template x509.Certificate
 	// key is the private key for which the certificate should emitted, or nil
 	// if the key should be generated. The private key is required (vs. the
 	// private one) because the Certificate might be attempted to be issued via
 	// self-signing.
 	key ed25519.PrivateKey
 }

 func (n *Namespace) etcdPath(f string, args ...interface{}) string {
 	return n.prefix + fmt.Sprintf(f, args...)
 }

 // New creates a new Certificate, or to be more precise, a promise that a
 // certificate will exist once Ensure is called.  Issuer must be a valid
 // certificate issuer (SelfSigned or another Certificate). Name must be unique
 // among all certificates, or empty (which will cause the certificate to be
 // volatile, ie. not stored in etcd).
 func (n *Namespace) New(issuer Issuer, name string, template x509.Certificate) *Certificate {
 	return &Certificate{
 		namespace: n,
 		Issuer:    issuer,
 		name:      name,
 		template:  template,
 	}
 }

 // Client makes a Kubernetes PKI-compatible client certificate template.
 // Directly derived from Kubernetes PKI requirements documented at
 //   https://kubernetes.io/docs/setup/best-practices/certificates/#configure-certificates-manually
 func Client(identity string, groups []string) x509.Certificate {
 	return x509.Certificate{
 		Subject: pkix.Name{
 			CommonName:   identity,
 			Organization: groups,
 		},
 		KeyUsage:    x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment,
 		ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth},
 	}
 }

 // Server makes a Kubernetes PKI-compatible server certificate template.
 func Server(dnsNames []string, ips []net.IP) x509.Certificate {
 	return x509.Certificate{
 		Subject:     pkix.Name{},
 		KeyUsage:    x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment,
 		ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
 		DNSNames:    dnsNames,
 		IPAddresses: ips,
 	}
 }

 // CA makes a Certificate that can sign other certificates.
 func CA(cn string) x509.Certificate {
 	return x509.Certificate{
 		Subject: pkix.Name{
 			CommonName: cn,
 		},
 		IsCA:        true,
 		KeyUsage:    x509.KeyUsageCertSign | x509.KeyUsageCRLSign | x509.KeyUsageDigitalSignature,
 		ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth, x509.ExtKeyUsageOCSPSigning},
 	}
 }

 func (c *Certificate) etcdPaths() (cert, key string) {
 	return c.namespace.etcdPath("%s-cert.der", c.name), c.namespace.etcdPath("%s-key.der", c.name)
 }

 func (c *Certificate) UseExistingKey(key ed25519.PrivateKey) {
 	c.key = key
 }

 // ensure returns a DER-encoded x509 certificate and internally encoded bare
 // ed25519 key for a given Certificate, in memory (if volatile), loading it
 // from etcd, or creating and saving it on etcd if needed.
 // This function is safe to call in parallel from multiple etcd clients
 // (including across machines), but it will error in case a concurrent
 // certificate generation happens. These errors are, however, safe to retry -
 // as long as all the certificate creators (ie., Metropolis nodes) run the same
 // version of this code.
 //
 // TODO(q3k): in the future, this should be handled better - especially as we
 // introduce new certificates, or worse, change the issuance chain. As a
 // stopgap measure, an explicit per-certificate or even global lock can be
 // implemented.  And, even before that, we can handle concurrency errors in a
 // smarter way.
 func (c *Certificate) ensure(ctx context.Context, kv clientv3.KV) (cert, key []byte, err error) {
 	if c.name == "" {
 		// Volatile certificate - generate.
 		// TODO(q3k): cache internally?
 		cert, key, err = c.Issuer.Issue(ctx, c, kv)
 		if err != nil {
 			err = fmt.Errorf("failed to issue: %w", err)
 			return
 		}
 		return
 	}

 	certPath, keyPath := c.etcdPaths()

 	// Try loading certificate and key from etcd.
 	certRes, err := kv.Get(ctx, certPath)
 	if err != nil {
 		err = fmt.Errorf("failed to get certificate from etcd: %w", err)
 		return
 	}
 	keyRes, err := kv.Get(ctx, keyPath)
 	if err != nil {
 		err = fmt.Errorf("failed to get key from etcd: %w", err)
 		return
 	}

 	if len(certRes.Kvs) == 1 && len(keyRes.Kvs) == 1 {
 		// Certificate and key exists in etcd, return that.
 		cert = certRes.Kvs[0].Value
 		key = keyRes.Kvs[0].Value

 		err = nil
 		// TODO(q3k): check for expiration
 		return
 	}

 	// No certificate found - issue one.
 	cert, key, err = c.Issuer.Issue(ctx, c, kv)
 	if err != nil {
 		err = fmt.Errorf("failed to issue: %w", err)
 		return
 	}

 	// Save to etcd in transaction. This ensures that no partial writes happen,
 	// and that we haven't been raced to the save.
 	res, err := kv.Txn(ctx).
 		If(
 			clientv3.Compare(clientv3.CreateRevision(certPath), "=", 0),
 			clientv3.Compare(clientv3.CreateRevision(keyPath), "=", 0),
 		).
 		Then(
 			clientv3.OpPut(certPath, string(cert)),
 			clientv3.OpPut(keyPath, string(key)),
 		).Commit()
 	if err != nil {
 		err = fmt.Errorf("failed to write newly issued certificate: %w", err)
 	} else if !res.Succeeded {
 		err = fmt.Errorf("certificate issuance transaction failed: concurrent write")
 	}

 	return
 }

 // Ensure returns an x509 DER-encoded (but not PEM-encoded) certificate and key
 // for a given Certificate.  If the certificate is volatile, each call to
 // Ensure will cause a new certificate to be generated.  Otherwise, it will be
 // retrieved from etcd, or generated and stored there if needed.
 func (c *Certificate) Ensure(ctx context.Context, kv clientv3.KV) (cert, key []byte, err error) {
 	cert, key, err = c.ensure(ctx, kv)
 	if err != nil {
 		return nil, nil, err
 	}
 	key, err = x509.MarshalPKCS8PrivateKey(ed25519.PrivateKey(key))
 	if err != nil {
 		err = fmt.Errorf("could not marshal private key (data corruption?): %w", err)
 		return
 	}
 	return cert, key, err
 }

 // FilesystemCertificate is a fileargs.FileArgs wrapper which will contain PEM
 // encoded certificate material when Mounted. This construct is useful when
 // dealing with services that want to access etcd-backed certificates as files
 // available locally.
 // Paths to the available files are considered opaque and should not be leaked
 // outside of the struct. Further restrictions on access to these files might
 // be imposed in the future.
 type FilesystemCertificate struct {
 	*fileargs.FileArgs
 	// CACertPath is the full path at which the CA certificate is available.
 	// Read only.
 	CACertPath string
 	// CertPath is the full path at which the certificate is available. Read
 	// only.
 	CertPath string
 	// KeyPath is the full path at which the key is available. Read only.
 	KeyPath string
 }

 // Mount returns a locally mounted FilesystemCertificate for this Certificate,
 // which allows services to access this Certificate via local filesystem
 // access.
 // The embeded fileargs.FileArgs can also be used to add additional file-backed
 // data under the same mount by calling ArgPath.
 // The returned FilesystemCertificate must be Closed in order to prevent a
 // system mount leak.
 func (c *Certificate) Mount(ctx context.Context, kv clientv3.KV) (*FilesystemCertificate, error) {
 	fa, err := fileargs.New()
 	if err != nil {
 		return nil, fmt.Errorf("when creating fileargs mount: %w", err)
 	}
 	fs := &FilesystemCertificate{FileArgs: fa}

 	cert, key, err := c.Ensure(ctx, kv)
 	if err != nil {
 		return nil, fmt.Errorf("when issuing certificate: %w", err)
 	}

 	cacert, err := c.Issuer.CACertificate(ctx, kv)
 	if err != nil {
 		return nil, fmt.Errorf("when getting issuer CA: %w", err)
 	}
 	// cacert will be null if this is a self-signed certificate.
 	if cacert == nil {
 		cacert = cert
 	}

 	fs.CACertPath = fs.ArgPath("ca.crt", pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: cacert}))
 	fs.CertPath = fs.ArgPath("tls.crt", pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: cert}))
 	fs.KeyPath = fs.ArgPath("tls.key", pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: key}))

 	return fs, nil
 }
	// Copyright 2020 The Monogon Project Authors.
	//
	// SPDX-License-Identifier: Apache-2.0
	//
	// 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 pki

	import (
	"context"
	"crypto/ed25519"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"net"

	"go.etcd.io/etcd/clientv3"

	"source.monogon.dev/metropolis/pkg/fileargs"
	)

	// Namespace represents some path in etcd where certificate/CA data will be
	// stored. Creating a namespace via Namespaced then permits the consumer of
	// this library to start creating certificates within this namespace.
	type Namespace struct {
	prefix string
	}

	// Namespaced creates a namespace for storing certificate data in etcd at a
	// given 'path' prefix.
	func Namespaced(prefix string) Namespace {
	return Namespace{
	prefix: prefix,
	}
	}

	// Certificate is the promise of a Certificate being available to the caller.
	// In this case, Certificate refers to a pair of x509 certificate and
	// corresponding private key. Certificates can be stored in etcd, and their
	// issuers might also be store on etcd. As such, this type's methods contain
	// references to an etcd KV client. This Certificate type is agnostic to
	// usage, but mostly geared towards Kubernetes certificates.
	type Certificate struct {
	namespace *Namespace

	// issuer is the Issuer that will generate this certificate if one doesn't
	// yet exist or etcd, or the requested certificate is volatile (not to be
	// stored on etcd).
	Issuer Issuer
	// name is a unique key for storing the certificate in etcd. If empty,
	// certificate is 'volatile', will not be stored on etcd, and every
	// .Ensure() call will generate a new pair.
	name string
	// template is an x509 certificate definition that will be used to generate
	// the certificate when issuing it.
	template x509.Certificate
	// key is the private key for which the certificate should emitted, or nil
	// if the key should be generated. The private key is required (vs. the
	// private one) because the Certificate might be attempted to be issued via
	// self-signing.
	key ed25519.PrivateKey
	}

	func (n *Namespace) etcdPath(f string, args ...interface{}) string {
	return n.prefix + fmt.Sprintf(f, args...)
	}

	// New creates a new Certificate, or to be more precise, a promise that a
	// certificate will exist once Ensure is called. Issuer must be a valid
	// certificate issuer (SelfSigned or another Certificate). Name must be unique
	// among all certificates, or empty (which will cause the certificate to be
	// volatile, ie. not stored in etcd).
	func (n Namespace) New(issuer Issuer, name string, template x509.Certificate) Certificate {
	return &Certificate{
	namespace: n,
	Issuer: issuer,
	name: name,
	template: template,
	}
	}

	// Client makes a Kubernetes PKI-compatible client certificate template.
	// Directly derived from Kubernetes PKI requirements documented at
	// https://kubernetes.io/docs/setup/best-practices/certificates/#configure-certificates-manually
	func Client(identity string, groups []string) x509.Certificate {
	return x509.Certificate{
	Subject: pkix.Name{
	CommonName: identity,
	Organization: groups,
	},
	KeyUsage: x509.KeyUsageDigitalSignature \| x509.KeyUsageKeyEncipherment,
	ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth},
	}
	}

	// Server makes a Kubernetes PKI-compatible server certificate template.
	func Server(dnsNames []string, ips []net.IP) x509.Certificate {
	return x509.Certificate{
	Subject: pkix.Name{},
	KeyUsage: x509.KeyUsageDigitalSignature \| x509.KeyUsageKeyEncipherment,
	ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
	DNSNames: dnsNames,
	IPAddresses: ips,
	}
	}

	// CA makes a Certificate that can sign other certificates.
	func CA(cn string) x509.Certificate {
	return x509.Certificate{
	Subject: pkix.Name{
	CommonName: cn,
	},
	IsCA: true,
	KeyUsage: x509.KeyUsageCertSign \| x509.KeyUsageCRLSign \| x509.KeyUsageDigitalSignature,
	ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth, x509.ExtKeyUsageOCSPSigning},
	}
	}

	func (c *Certificate) etcdPaths() (cert, key string) {
	return c.namespace.etcdPath("%s-cert.der", c.name), c.namespace.etcdPath("%s-key.der", c.name)
	}

	func (c *Certificate) UseExistingKey(key ed25519.PrivateKey) {
	c.key = key
	}

	// ensure returns a DER-encoded x509 certificate and internally encoded bare
	// ed25519 key for a given Certificate, in memory (if volatile), loading it
	// from etcd, or creating and saving it on etcd if needed.
	// This function is safe to call in parallel from multiple etcd clients
	// (including across machines), but it will error in case a concurrent
	// certificate generation happens. These errors are, however, safe to retry -
	// as long as all the certificate creators (ie., Metropolis nodes) run the same
	// version of this code.
	//
	// TODO(q3k): in the future, this should be handled better - especially as we
	// introduce new certificates, or worse, change the issuance chain. As a
	// stopgap measure, an explicit per-certificate or even global lock can be
	// implemented. And, even before that, we can handle concurrency errors in a
	// smarter way.
	func (c *Certificate) ensure(ctx context.Context, kv clientv3.KV) (cert, key []byte, err error) {
	if c.name == "" {
	// Volatile certificate - generate.
	// TODO(q3k): cache internally?
	cert, key, err = c.Issuer.Issue(ctx, c, kv)
	if err != nil {
	err = fmt.Errorf("failed to issue: %w", err)
	return
	}
	return
	}

	certPath, keyPath := c.etcdPaths()

	// Try loading certificate and key from etcd.
	certRes, err := kv.Get(ctx, certPath)
	if err != nil {
	err = fmt.Errorf("failed to get certificate from etcd: %w", err)
	return
	}
	keyRes, err := kv.Get(ctx, keyPath)
	if err != nil {
	err = fmt.Errorf("failed to get key from etcd: %w", err)
	return
	}

	if len(certRes.Kvs) == 1 && len(keyRes.Kvs) == 1 {
	// Certificate and key exists in etcd, return that.
	cert = certRes.Kvs[0].Value
	key = keyRes.Kvs[0].Value

	err = nil
	// TODO(q3k): check for expiration
	return
	}

	// No certificate found - issue one.
	cert, key, err = c.Issuer.Issue(ctx, c, kv)
	if err != nil {
	err = fmt.Errorf("failed to issue: %w", err)
	return
	}

	// Save to etcd in transaction. This ensures that no partial writes happen,
	// and that we haven't been raced to the save.
	res, err := kv.Txn(ctx).
	If(
	clientv3.Compare(clientv3.CreateRevision(certPath), "=", 0),
	clientv3.Compare(clientv3.CreateRevision(keyPath), "=", 0),
	).
	Then(
	clientv3.OpPut(certPath, string(cert)),
	clientv3.OpPut(keyPath, string(key)),
	).Commit()
	if err != nil {
	err = fmt.Errorf("failed to write newly issued certificate: %w", err)
	} else if !res.Succeeded {
	err = fmt.Errorf("certificate issuance transaction failed: concurrent write")
	}

	return
	}

	// Ensure returns an x509 DER-encoded (but not PEM-encoded) certificate and key
	// for a given Certificate. If the certificate is volatile, each call to
	// Ensure will cause a new certificate to be generated. Otherwise, it will be
	// retrieved from etcd, or generated and stored there if needed.
	func (c *Certificate) Ensure(ctx context.Context, kv clientv3.KV) (cert, key []byte, err error) {
	cert, key, err = c.ensure(ctx, kv)
	if err != nil {
	return nil, nil, err
	}
	key, err = x509.MarshalPKCS8PrivateKey(ed25519.PrivateKey(key))
	if err != nil {
	err = fmt.Errorf("could not marshal private key (data corruption?): %w", err)
	return
	}
	return cert, key, err
	}

	// FilesystemCertificate is a fileargs.FileArgs wrapper which will contain PEM
	// encoded certificate material when Mounted. This construct is useful when
	// dealing with services that want to access etcd-backed certificates as files
	// available locally.
	// Paths to the available files are considered opaque and should not be leaked
	// outside of the struct. Further restrictions on access to these files might
	// be imposed in the future.
	type FilesystemCertificate struct {
	*fileargs.FileArgs
	// CACertPath is the full path at which the CA certificate is available.
	// Read only.
	CACertPath string
	// CertPath is the full path at which the certificate is available. Read
	// only.
	CertPath string
	// KeyPath is the full path at which the key is available. Read only.
	KeyPath string
	}

	// Mount returns a locally mounted FilesystemCertificate for this Certificate,
	// which allows services to access this Certificate via local filesystem
	// access.
	// The embeded fileargs.FileArgs can also be used to add additional file-backed
	// data under the same mount by calling ArgPath.
	// The returned FilesystemCertificate must be Closed in order to prevent a
	// system mount leak.
	func (c Certificate) Mount(ctx context.Context, kv clientv3.KV) (FilesystemCertificate, error) {
	fa, err := fileargs.New()
	if err != nil {
	return nil, fmt.Errorf("when creating fileargs mount: %w", err)
	}
	fs := &FilesystemCertificate{FileArgs: fa}

	cert, key, err := c.Ensure(ctx, kv)
	if err != nil {
	return nil, fmt.Errorf("when issuing certificate: %w", err)
	}

	cacert, err := c.Issuer.CACertificate(ctx, kv)
	if err != nil {
	return nil, fmt.Errorf("when getting issuer CA: %w", err)
	}
	// cacert will be null if this is a self-signed certificate.
	if cacert == nil {
	cacert = cert
	}

	fs.CACertPath = fs.ArgPath("ca.crt", pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: cacert}))
	fs.CertPath = fs.ArgPath("tls.crt", pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: cert}))
	fs.KeyPath = fs.ArgPath("tls.key", pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: key}))

	return fs, nil
	}