smallstep-certificates/authority/provisioner/aws.go
2019-06-07 11:24:56 -07:00

428 lines
14 KiB
Go

package provisioner
import (
"crypto/sha256"
"crypto/x509"
"encoding/base64"
"encoding/hex"
"encoding/json"
"encoding/pem"
"fmt"
"io/ioutil"
"net"
"net/http"
"strings"
"time"
"github.com/pkg/errors"
"github.com/smallstep/cli/jose"
)
// awsIssuer is the string used as issuer in the generated tokens.
const awsIssuer = "ec2.amazonaws.com"
// awsIdentityURL is the url used to retrieve the instance identity document.
const awsIdentityURL = "http://169.254.169.254/latest/dynamic/instance-identity/document"
// awsSignatureURL is the url used to retrieve the instance identity signature.
const awsSignatureURL = "http://169.254.169.254/latest/dynamic/instance-identity/signature"
// awsCertificate is the certificate used to validate the instance identity
// signature.
const awsCertificate = `-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----`
// awsSignatureAlgorithm is the signature algorithm used to verify the identity
// document signature.
const awsSignatureAlgorithm = x509.SHA256WithRSA
type awsConfig struct {
identityURL string
signatureURL string
certificate *x509.Certificate
signatureAlgorithm x509.SignatureAlgorithm
}
func newAWSConfig() (*awsConfig, error) {
block, _ := pem.Decode([]byte(awsCertificate))
if block == nil || block.Type != "CERTIFICATE" {
return nil, errors.New("error decoding AWS certificate")
}
cert, err := x509.ParseCertificate(block.Bytes)
if err != nil {
return nil, errors.Wrap(err, "error parsing AWS certificate")
}
return &awsConfig{
identityURL: awsIdentityURL,
signatureURL: awsSignatureURL,
certificate: cert,
signatureAlgorithm: awsSignatureAlgorithm,
}, nil
}
type awsPayload struct {
jose.Claims
Amazon awsAmazonPayload `json:"amazon"`
SANs []string `json:"sans"`
document awsInstanceIdentityDocument
}
type awsAmazonPayload struct {
Document []byte `json:"document"`
Signature []byte `json:"signature"`
}
type awsInstanceIdentityDocument struct {
AccountID string `json:"accountId"`
Architecture string `json:"architecture"`
AvailabilityZone string `json:"availabilityZone"`
BillingProducts []string `json:"billingProducts"`
DevpayProductCodes []string `json:"devpayProductCodes"`
ImageID string `json:"imageId"`
InstanceID string `json:"instanceId"`
InstanceType string `json:"instanceType"`
KernelID string `json:"kernelId"`
PendingTime time.Time `json:"pendingTime"`
PrivateIP string `json:"privateIp"`
RamdiskID string `json:"ramdiskId"`
Region string `json:"region"`
Version string `json:"version"`
}
// AWS is the provisioner that supports identity tokens created from the Amazon
// Web Services Instance Identity Documents.
//
// If DisableCustomSANs is true, only the internal DNS and IP will be added as a
// SAN. By default it will accept any SAN in the CSR.
//
// If DisableTrustOnFirstUse is true, multiple sign request for this provisioner
// with the same instance will be accepted. By default only the first request
// will be accepted.
//
// If InstanceAge is set, only the instances with a pendingTime within the given
// period will be accepted.
//
// Amazon Identity docs are available at
// https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/instance-identity-documents.html
type AWS struct {
Type string `json:"type"`
Name string `json:"name"`
Accounts []string `json:"accounts"`
DisableCustomSANs bool `json:"disableCustomSANs"`
DisableTrustOnFirstUse bool `json:"disableTrustOnFirstUse"`
InstanceAge Duration `json:"instanceAge,omitempty"`
Claims *Claims `json:"claims,omitempty"`
claimer *Claimer
config *awsConfig
audiences Audiences
}
// GetID returns the provisioner unique identifier.
func (p *AWS) GetID() string {
return "aws/" + p.Name
}
// GetTokenID returns the identifier of the token.
func (p *AWS) GetTokenID(token string) (string, error) {
payload, err := p.authorizeToken(token)
if err != nil {
return "", err
}
// If TOFU is disabled create an ID for the token, so it cannot be reused.
// The timestamps, document and signatures should be mostly unique.
if p.DisableTrustOnFirstUse {
sum := sha256.Sum256([]byte(token))
return strings.ToLower(hex.EncodeToString(sum[:])), nil
}
return payload.ID, nil
}
// GetName returns the name of the provisioner.
func (p *AWS) GetName() string {
return p.Name
}
// GetType returns the type of provisioner.
func (p *AWS) GetType() Type {
return TypeAWS
}
// GetEncryptedKey is not available in an AWS provisioner.
func (p *AWS) GetEncryptedKey() (kid string, key string, ok bool) {
return "", "", false
}
// GetIdentityToken retrieves the identity document and it's signature and
// generates a token with them.
func (p *AWS) GetIdentityToken(caURL string) (string, error) {
// Initialize the config if this method is used from the cli.
if err := p.assertConfig(); err != nil {
return "", err
}
var idoc awsInstanceIdentityDocument
doc, err := p.readURL(p.config.identityURL)
if err != nil {
return "", errors.Wrap(err, "error retrieving identity document, are you in an AWS VM?")
}
if err := json.Unmarshal(doc, &idoc); err != nil {
return "", errors.Wrap(err, "error unmarshaling identity document")
}
sig, err := p.readURL(p.config.signatureURL)
if err != nil {
return "", errors.Wrap(err, "error retrieving identity document signature, are you in an AWS VM?")
}
signature, err := base64.StdEncoding.DecodeString(string(sig))
if err != nil {
return "", errors.Wrap(err, "error decoding identity document signature")
}
if err := p.checkSignature(doc, signature); err != nil {
return "", err
}
audience, err := generateSignAudience(caURL, p.GetID())
if err != nil {
return "", err
}
// Create unique ID for Trust On First Use (TOFU). Only the first instance
// per provisioner is allowed as we don't have a way to trust the given
// sans.
unique := fmt.Sprintf("%s.%s", p.GetID(), idoc.InstanceID)
sum := sha256.Sum256([]byte(unique))
// Create a JWT from the identity document
signer, err := jose.NewSigner(
jose.SigningKey{Algorithm: jose.HS256, Key: signature},
new(jose.SignerOptions).WithType("JWT"),
)
if err != nil {
return "", errors.Wrap(err, "error creating signer")
}
now := time.Now()
payload := awsPayload{
Claims: jose.Claims{
Issuer: awsIssuer,
Subject: idoc.InstanceID,
Audience: []string{audience},
Expiry: jose.NewNumericDate(now.Add(5 * time.Minute)),
NotBefore: jose.NewNumericDate(now),
IssuedAt: jose.NewNumericDate(now),
ID: strings.ToLower(hex.EncodeToString(sum[:])),
},
Amazon: awsAmazonPayload{
Document: doc,
Signature: signature,
},
}
tok, err := jose.Signed(signer).Claims(payload).CompactSerialize()
if err != nil {
return "", errors.Wrap(err, "error serialiazing token")
}
return tok, nil
}
// Init validates and initializes the AWS provisioner.
func (p *AWS) 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")
case p.InstanceAge.Value() < 0:
return errors.New("provisioner instanceAge cannot be negative")
}
// Update claims with global ones
if p.claimer, err = NewClaimer(p.Claims, config.Claims); err != nil {
return err
}
// Add default config
if p.config, err = newAWSConfig(); err != nil {
return err
}
p.audiences = config.Audiences.WithFragment(p.GetID())
return nil
}
// AuthorizeSign validates the given token and returns the sign options that
// will be used on certificate creation.
func (p *AWS) AuthorizeSign(token string) ([]SignOption, error) {
payload, err := p.authorizeToken(token)
if err != nil {
return nil, err
}
doc := payload.document
// Enforce default DNS and IP if configured.
// By default we'll accept the SANs in the CSR.
// There's no way to trust them other than TOFU.
var so []SignOption
if p.DisableCustomSANs {
so = append(so, dnsNamesValidator([]string{
fmt.Sprintf("ip-%s.%s.compute.internal", strings.Replace(doc.PrivateIP, ".", "-", -1), doc.Region),
}))
so = append(so, ipAddressesValidator([]net.IP{
net.ParseIP(doc.PrivateIP),
}))
}
return append(so,
commonNameValidator(doc.InstanceID),
profileDefaultDuration(p.claimer.DefaultTLSCertDuration()),
newProvisionerExtensionOption(TypeAWS, p.Name, doc.AccountID),
newValidityValidator(p.claimer.MinTLSCertDuration(), p.claimer.MaxTLSCertDuration()),
), nil
}
// AuthorizeRenewal returns an error if the renewal is disabled.
func (p *AWS) AuthorizeRenewal(cert *x509.Certificate) error {
if p.claimer.IsDisableRenewal() {
return errors.Errorf("renew is disabled for provisioner %s", p.GetID())
}
return nil
}
// AuthorizeRevoke returns an error because revoke is not supported on AWS
// provisioners.
func (p *AWS) AuthorizeRevoke(token string) error {
return errors.New("revoke is not supported on a AWS provisioner")
}
// assertConfig initializes the config if it has not been initialized
func (p *AWS) assertConfig() (err error) {
if p.config != nil {
return
}
p.config, err = newAWSConfig()
return err
}
// checkSignature returns an error if the signature is not valid.
func (p *AWS) checkSignature(signed, signature []byte) error {
if err := p.config.certificate.CheckSignature(p.config.signatureAlgorithm, signed, signature); err != nil {
return errors.Wrap(err, "error validating identity document signature")
}
return nil
}
// readURL does a GET request to the given url and returns the body. It's not
// using pkg/errors to avoid verbose errors, the caller should use it and write
// the appropriate error.
func (p *AWS) readURL(url string) ([]byte, error) {
r, err := http.Get(url)
if err != nil {
return nil, err
}
defer r.Body.Close()
b, err := ioutil.ReadAll(r.Body)
if err != nil {
return nil, err
}
return b, nil
}
// 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 *AWS) authorizeToken(token string) (*awsPayload, error) {
jwt, err := jose.ParseSigned(token)
if err != nil {
return nil, errors.Wrapf(err, "error parsing token")
}
if len(jwt.Headers) == 0 {
return nil, errors.New("error parsing token: header is missing")
}
var unsafeClaims awsPayload
if err := jwt.UnsafeClaimsWithoutVerification(&unsafeClaims); err != nil {
return nil, errors.Wrap(err, "error unmarshaling claims")
}
var payload awsPayload
if err := jwt.Claims(unsafeClaims.Amazon.Signature, &payload); err != nil {
return nil, errors.Wrap(err, "error verifying claims")
}
// Validate identity document signature
if err := p.checkSignature(payload.Amazon.Document, payload.Amazon.Signature); err != nil {
return nil, err
}
var doc awsInstanceIdentityDocument
if err := json.Unmarshal(payload.Amazon.Document, &doc); err != nil {
return nil, errors.Wrap(err, "error unmarshaling identity document")
}
switch {
case doc.AccountID == "":
return nil, errors.New("identity document accountId cannot be empty")
case doc.InstanceID == "":
return nil, errors.New("identity document instanceId cannot be empty")
case doc.PrivateIP == "":
return nil, errors.New("identity document privateIp cannot be empty")
case doc.Region == "":
return nil, errors.New("identity document region cannot be empty")
}
// According to "rfc7519 JSON Web Token" acceptable skew should be no
// more than a few minutes.
now := time.Now().UTC()
if err = payload.ValidateWithLeeway(jose.Expected{
Issuer: awsIssuer,
Subject: doc.InstanceID,
Time: now,
}, time.Minute); err != nil {
return nil, errors.Wrapf(err, "invalid token")
}
// validate audiences with the defaults
if !matchesAudience(payload.Audience, p.audiences.Sign) {
fmt.Println(payload.Audience, "vs", p.audiences.Sign)
return nil, errors.New("invalid token: invalid audience claim (aud)")
}
// validate accounts
if len(p.Accounts) > 0 {
var found bool
for _, sa := range p.Accounts {
if sa == doc.AccountID {
found = true
break
}
}
if !found {
return nil, errors.New("invalid identity document: accountId is not valid")
}
}
// validate instance age
if d := p.InstanceAge.Value(); d > 0 {
if now.Sub(doc.PendingTime) > d {
return nil, errors.New("identity document pendingTime is too old")
}
}
payload.document = doc
return &payload, nil
}