certificates/authority/provisioner/k8sSA.go
Herman Slatman 512b8d6730
Refactor instantiation of policy engines
Instead of using the `base` struct, the x509 and SSH policy
engines are now added to each provisioner directly.
2022-01-25 16:45:25 +01:00

334 lines
11 KiB
Go

package provisioner
import (
"context"
"crypto/ecdsa"
"crypto/ed25519"
"crypto/rsa"
"crypto/x509"
"encoding/pem"
"net/http"
"github.com/pkg/errors"
"github.com/smallstep/certificates/errs"
"github.com/smallstep/certificates/policy"
"go.step.sm/crypto/jose"
"go.step.sm/crypto/pemutil"
"go.step.sm/crypto/sshutil"
"go.step.sm/crypto/x509util"
)
// NOTE: There can be at most one kubernetes service account provisioner configured
// per instance of step-ca. This is due to a lack of distinguishing information
// contained in kubernetes service account tokens.
const (
// K8sSAName is the default name used for kubernetes service account provisioners.
K8sSAName = "k8sSA-default"
// K8sSAID is the default ID for kubernetes service account provisioners.
K8sSAID = "k8ssa/" + K8sSAName
k8sSAIssuer = "kubernetes/serviceaccount"
)
// jwtPayload extends jwt.Claims with step attributes.
type k8sSAPayload struct {
jose.Claims
Namespace string `json:"kubernetes.io/serviceaccount/namespace,omitempty"`
SecretName string `json:"kubernetes.io/serviceaccount/secret.name,omitempty"`
ServiceAccountName string `json:"kubernetes.io/serviceaccount/service-account.name,omitempty"`
ServiceAccountUID string `json:"kubernetes.io/serviceaccount/service-account.uid,omitempty"`
}
// K8sSA represents a Kubernetes ServiceAccount provisioner; an
// entity trusted to make signature requests.
type K8sSA struct {
*base
ID string `json:"-"`
Type string `json:"type"`
Name string `json:"name"`
PubKeys []byte `json:"publicKeys,omitempty"`
Claims *Claims `json:"claims,omitempty"`
Options *Options `json:"options,omitempty"`
claimer *Claimer
audiences Audiences
//kauthn kauthn.AuthenticationV1Interface
pubKeys []interface{}
x509Policy policy.X509NamePolicyEngine
sshPolicy policy.SSHNamePolicyEngine
}
// GetID returns the provisioner unique identifier. The name and credential id
// should uniquely identify any K8sSA provisioner.
func (p *K8sSA) GetID() string {
if p.ID != "" {
return p.ID
}
return p.GetIDForToken()
}
// GetIDForToken returns an identifier that will be used to load the provisioner
// from a token.
func (p *K8sSA) GetIDForToken() string {
return K8sSAID
}
// GetTokenID returns an unimplemented error and does not use the input ott.
func (p *K8sSA) GetTokenID(ott string) (string, error) {
return "", errors.New("not implemented")
}
// GetName returns the name of the provisioner.
func (p *K8sSA) GetName() string {
return p.Name
}
// GetType returns the type of provisioner.
func (p *K8sSA) GetType() Type {
return TypeK8sSA
}
// GetEncryptedKey returns false, because the kubernetes provisioner does not
// have access to the private key.
func (p *K8sSA) GetEncryptedKey() (string, string, bool) {
return "", "", false
}
// Init initializes and validates the fields of a K8sSA type.
func (p *K8sSA) Init(config Config) (err error) {
switch {
case p.Type == "":
return errors.New("provisioner type cannot be empty")
case p.Name == "":
return errors.New("provisioner name cannot be empty")
}
if p.PubKeys != nil {
var (
block *pem.Block
rest = p.PubKeys
)
for rest != nil {
block, rest = pem.Decode(rest)
if block == nil {
break
}
key, err := pemutil.ParseKey(pem.EncodeToMemory(block))
if err != nil {
return errors.Wrapf(err, "error parsing public key in provisioner '%s'", p.GetName())
}
switch q := key.(type) {
case *rsa.PublicKey, *ecdsa.PublicKey, ed25519.PublicKey:
default:
return errors.Errorf("Unexpected public key type %T in provisioner '%s'", q, p.GetName())
}
p.pubKeys = append(p.pubKeys, key)
}
} else {
// TODO: Use the TokenReview API if no pub keys provided. This will need to
// be configured with additional attributes in the K8sSA struct for
// connecting to the kubernetes API server.
return errors.New("K8s Service Account provisioner cannot be initialized without pub keys")
}
/*
// NOTE: Not sure if we should be doing this initialization here ...
// If you have a k8sSA provisioner defined in your config, but you're not
// in a kubernetes pod then your CA will fail to startup. Maybe we just postpone
// creating the authn until token validation time?
if err := checkAccess(k8s.AuthorizationV1()); err != nil {
return errors.Wrapf(err, "error verifying access to kubernetes authz service for provisioner %s", p.GetID())
}
p.kauthn = k8s.AuthenticationV1()
*/
// Update claims with global ones
if p.claimer, err = NewClaimer(p.Claims, config.Claims); err != nil {
return err
}
// Initialize the x509 allow/deny policy engine
if p.x509Policy, err = newX509PolicyEngine(p.Options.GetX509Options()); err != nil {
return err
}
// Initialize the SSH allow/deny policy engine
if p.sshPolicy, err = newSSHPolicyEngine(p.Options.GetSSHOptions()); err != nil {
return err
}
p.audiences = config.Audiences
return err
}
// authorizeToken performs common jwt authorization actions and returns the
// claims for case specific downstream parsing.
// e.g. a Sign request will auth/validate different fields than a Revoke request.
func (p *K8sSA) authorizeToken(token string, audiences []string) (*k8sSAPayload, error) {
jwt, err := jose.ParseSigned(token)
if err != nil {
return nil, errs.Wrap(http.StatusUnauthorized, err,
"k8ssa.authorizeToken; error parsing k8sSA token")
}
var (
valid bool
claims k8sSAPayload
)
if p.pubKeys == nil {
return nil, errs.Unauthorized("k8ssa.authorizeToken; k8sSA TokenReview API integration not implemented")
/* NOTE: We plan to support the TokenReview API in a future release.
Below is some code that should be useful when we prioritize
this integration.
tr := kauthnApi.TokenReview{Spec: kauthnApi.TokenReviewSpec{Token: string(token)}}
rvw, err := p.kauthn.TokenReviews().Create(&tr)
if err != nil {
return nil, errors.Wrap(err, "error using kubernetes TokenReview API")
}
if rvw.Status.Error != "" {
return nil, errors.Errorf("error from kubernetes TokenReviewAPI: %s", rvw.Status.Error)
}
if !rvw.Status.Authenticated {
return nil, errors.New("error from kubernetes TokenReviewAPI: token could not be authenticated")
}
if err = jwt.UnsafeClaimsWithoutVerification(&claims); err != nil {
return nil, errors.Wrap(err, "error parsing claims")
}
*/
}
for _, pk := range p.pubKeys {
if err = jwt.Claims(pk, &claims); err == nil {
valid = true
break
}
}
if !valid {
return nil, errs.Unauthorized("k8ssa.authorizeToken; error validating k8sSA token and extracting claims")
}
// According to "rfc7519 JSON Web Token" acceptable skew should be no
// more than a few minutes.
if err = claims.Validate(jose.Expected{
Issuer: k8sSAIssuer,
}); err != nil {
return nil, errs.Wrap(http.StatusUnauthorized, err, "k8ssa.authorizeToken; invalid k8sSA token claims")
}
if claims.Subject == "" {
return nil, errs.Unauthorized("k8ssa.authorizeToken; k8sSA token subject cannot be empty")
}
return &claims, nil
}
// AuthorizeRevoke returns an error if the provisioner does not have rights to
// revoke the certificate with serial number in the `sub` property.
func (p *K8sSA) AuthorizeRevoke(ctx context.Context, token string) error {
_, err := p.authorizeToken(token, p.audiences.Revoke)
return errs.Wrap(http.StatusInternalServerError, err, "k8ssa.AuthorizeRevoke")
}
// AuthorizeSign validates the given token.
func (p *K8sSA) AuthorizeSign(ctx context.Context, token string) ([]SignOption, error) {
claims, err := p.authorizeToken(token, p.audiences.Sign)
if err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "k8ssa.AuthorizeSign")
}
// Add some values to use in custom templates.
data := x509util.NewTemplateData()
data.SetCommonName(claims.ServiceAccountName)
if v, err := unsafeParseSigned(token); err == nil {
data.SetToken(v)
}
// Certificate templates: on K8sSA the default template is the certificate
// request.
templateOptions, err := CustomTemplateOptions(p.Options, data, x509util.DefaultAdminLeafTemplate)
if err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "k8ssa.AuthorizeSign")
}
return []SignOption{
templateOptions,
// modifiers / withOptions
newProvisionerExtensionOption(TypeK8sSA, p.Name, ""),
profileDefaultDuration(p.claimer.DefaultTLSCertDuration()),
// validators
defaultPublicKeyValidator{},
newValidityValidator(p.claimer.MinTLSCertDuration(), p.claimer.MaxTLSCertDuration()),
newX509NamePolicyValidator(p.x509Policy),
}, nil
}
// AuthorizeRenew returns an error if the renewal is disabled.
func (p *K8sSA) AuthorizeRenew(ctx context.Context, cert *x509.Certificate) error {
if p.claimer.IsDisableRenewal() {
return errs.Unauthorized("k8ssa.AuthorizeRenew; renew is disabled for k8sSA provisioner '%s'", p.GetName())
}
return nil
}
// AuthorizeSSHSign validates an request for an SSH certificate.
func (p *K8sSA) AuthorizeSSHSign(ctx context.Context, token string) ([]SignOption, error) {
if !p.claimer.IsSSHCAEnabled() {
return nil, errs.Unauthorized("k8ssa.AuthorizeSSHSign; sshCA is disabled for k8sSA provisioner '%s'", p.GetName())
}
claims, err := p.authorizeToken(token, p.audiences.SSHSign)
if err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "k8ssa.AuthorizeSSHSign")
}
// Certificate templates.
// Set some default variables to be used in the templates.
data := sshutil.CreateTemplateData(sshutil.HostCert, claims.ServiceAccountName, []string{claims.ServiceAccountName})
if v, err := unsafeParseSigned(token); err == nil {
data.SetToken(v)
}
templateOptions, err := CustomSSHTemplateOptions(p.Options, data, sshutil.CertificateRequestTemplate)
if err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "k8ssa.AuthorizeSSHSign")
}
signOptions := []SignOption{templateOptions}
return append(signOptions,
// Require type, key-id and principals in the SignSSHOptions.
&sshCertOptionsRequireValidator{CertType: true, KeyID: true, Principals: true},
// Set the validity bounds if not set.
&sshDefaultDuration{p.claimer},
// Validate public key
&sshDefaultPublicKeyValidator{},
// Validate the validity period.
&sshCertValidityValidator{p.claimer},
// Require and validate all the default fields in the SSH certificate.
&sshCertDefaultValidator{},
// Ensure that all principal names are allowed
newSSHNamePolicyValidator(p.sshPolicy),
), nil
}
/*
func checkAccess(authz kauthz.AuthorizationV1Interface) error {
r := &kauthzApi.SelfSubjectAccessReview{
Spec: kauthzApi.SelfSubjectAccessReviewSpec{
ResourceAttributes: &kauthzApi.ResourceAttributes{
Group: "authentication.k8s.io",
Version: "v1",
Resource: "tokenreviews",
Verb: "create",
},
},
}
rvw, err := authz.SelfSubjectAccessReviews().Create(r)
if err != nil {
return err
}
if !rvw.Status.Allowed {
return fmt.Errorf("Unable to create kubernetes token reviews: %s", rvw.Status.Reason)
}
return nil
}
*/