package provisioner import ( "context" "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/certificates/errs" "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" // awsAPITokenURL is the url used to get the IMDSv2 API token const awsAPITokenURL = "http://169.254.169.254/latest/api/token" // awsAPITokenTTL is the default TTL to use when requesting IMDSv2 API tokens // -- we keep this short-lived since we get a new token with every call to readURL() const awsAPITokenTTL = "30" // awsMetadataTokenHeader is the header that must be passed with every IMDSv2 request const awsMetadataTokenHeader = "X-aws-ec2-metadata-token" // awsMetadataTokenTTLHeader is the header used to indicate the token TTL requested const awsMetadataTokenTTLHeader = "X-aws-ec2-metadata-token-ttl-seconds" // awsCertificate is the certificate used to validate the instance identity // signature. const awsCertificate = `-----BEGIN CERTIFICATE----- MIIDIjCCAougAwIBAgIJAKnL4UEDMN/FMA0GCSqGSIb3DQEBBQUAMGoxCzAJBgNV BAYTAlVTMRMwEQYDVQQIEwpXYXNoaW5ndG9uMRAwDgYDVQQHEwdTZWF0dGxlMRgw FgYDVQQKEw9BbWF6b24uY29tIEluYy4xGjAYBgNVBAMTEWVjMi5hbWF6b25hd3Mu Y29tMB4XDTE0MDYwNTE0MjgwMloXDTI0MDYwNTE0MjgwMlowajELMAkGA1UEBhMC VVMxEzARBgNVBAgTCldhc2hpbmd0b24xEDAOBgNVBAcTB1NlYXR0bGUxGDAWBgNV BAoTD0FtYXpvbi5jb20gSW5jLjEaMBgGA1UEAxMRZWMyLmFtYXpvbmF3cy5jb20w gZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJAoGBAIe9GN//SRK2knbjySG0ho3yqQM3 e2TDhWO8D2e8+XZqck754gFSo99AbT2RmXClambI7xsYHZFapbELC4H91ycihvrD jbST1ZjkLQgga0NE1q43eS68ZeTDccScXQSNivSlzJZS8HJZjgqzBlXjZftjtdJL XeE4hwvo0sD4f3j9AgMBAAGjgc8wgcwwHQYDVR0OBBYEFCXWzAgVyrbwnFncFFIs 77VBdlE4MIGcBgNVHSMEgZQwgZGAFCXWzAgVyrbwnFncFFIs77VBdlE4oW6kbDBq MQswCQYDVQQGEwJVUzETMBEGA1UECBMKV2FzaGluZ3RvbjEQMA4GA1UEBxMHU2Vh dHRsZTEYMBYGA1UEChMPQW1hem9uLmNvbSBJbmMuMRowGAYDVQQDExFlYzIuYW1h em9uYXdzLmNvbYIJAKnL4UEDMN/FMAwGA1UdEwQFMAMBAf8wDQYJKoZIhvcNAQEF BQADgYEAFYcz1OgEhQBXIwIdsgCOS8vEtiJYF+j9uO6jz7VOmJqO+pRlAbRlvY8T C1haGgSI/A1uZUKs/Zfnph0oEI0/hu1IIJ/SKBDtN5lvmZ/IzbOPIJWirlsllQIQ 7zvWbGd9c9+Rm3p04oTvhup99la7kZqevJK0QRdD/6NpCKsqP/0= -----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 { *base 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(subject, 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: subject, 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(ctx context.Context, token string) ([]SignOption, error) { payload, err := p.authorizeToken(token) if err != nil { return nil, errs.Wrap(http.StatusInternalServerError, err, "aws.AuthorizeSign") } doc := payload.document // Enforce known CN and default DNS and IP if configured. // By default we'll accept the CN and 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, // modifiers / withOptions newProvisionerExtensionOption(TypeAWS, p.Name, doc.AccountID, "InstanceID", doc.InstanceID), profileDefaultDuration(p.claimer.DefaultTLSCertDuration()), // validators defaultPublicKeyValidator{}, commonNameValidator(payload.Claims.Subject), newValidityValidator(p.claimer.MinTLSCertDuration(), p.claimer.MaxTLSCertDuration()), ), nil } // AuthorizeRenew returns an error if the renewal is disabled. // NOTE: This method does not actually validate the certificate or check it's // revocation status. Just confirms that the provisioner that created the // certificate was configured to allow renewals. func (p *AWS) AuthorizeRenew(ctx context.Context, cert *x509.Certificate) error { if p.claimer.IsDisableRenewal() { return errs.Unauthorized("aws.AuthorizeRenew; renew is disabled for aws provisioner %s", p.GetID()) } return nil } // 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) { client := &http.Client{} // get authorization token req, err := http.NewRequest(http.MethodPut, awsAPITokenURL, nil) if err != nil { return nil, err } req.Header.Set(awsMetadataTokenTTLHeader, awsAPITokenTTL) r, err := client.Do(req) if err != nil { return nil, err } defer r.Body.Close() b, err := ioutil.ReadAll(r.Body) if err != nil { return nil, err } token := string(b) // now get the data req, err = http.NewRequest(http.MethodGet, url, nil) if err != nil { return nil, err } req.Header.Set(awsMetadataTokenHeader, token) r, err = client.Do(req) 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, errs.Wrapf(http.StatusUnauthorized, err, "aws.authorizeToken; error parsing aws token") } if len(jwt.Headers) == 0 { return nil, errs.InternalServer("aws.authorizeToken; error parsing token, header is missing") } var unsafeClaims awsPayload if err := jwt.UnsafeClaimsWithoutVerification(&unsafeClaims); err != nil { return nil, errs.Wrap(http.StatusUnauthorized, err, "aws.authorizeToken; error unmarshaling claims") } var payload awsPayload if err := jwt.Claims(unsafeClaims.Amazon.Signature, &payload); err != nil { return nil, errs.Wrap(http.StatusUnauthorized, err, "aws.authorizeToken; error verifying claims") } // Validate identity document signature if err := p.checkSignature(payload.Amazon.Document, payload.Amazon.Signature); err != nil { return nil, errs.Wrap(http.StatusUnauthorized, err, "aws.authorizeToken; invalid aws token signature") } var doc awsInstanceIdentityDocument if err := json.Unmarshal(payload.Amazon.Document, &doc); err != nil { return nil, errs.Wrap(http.StatusUnauthorized, err, "aws.authorizeToken; error unmarshaling aws identity document") } switch { case doc.AccountID == "": return nil, errs.Unauthorized("aws.authorizeToken; aws identity document accountId cannot be empty") case doc.InstanceID == "": return nil, errs.Unauthorized("aws.authorizeToken; aws identity document instanceId cannot be empty") case doc.PrivateIP == "": return nil, errs.Unauthorized("aws.authorizeToken; aws identity document privateIp cannot be empty") case doc.Region == "": return nil, errs.Unauthorized("aws.authorizeToken; aws 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, Time: now, }, time.Minute); err != nil { return nil, errs.Wrapf(http.StatusUnauthorized, err, "aws.authorizeToken; invalid aws token") } // validate audiences with the defaults if !matchesAudience(payload.Audience, p.audiences.Sign) { return nil, errs.Unauthorized("aws.authorizeToken; invalid token - invalid audience claim (aud)") } // Validate subject, it has to be known if disableCustomSANs is enabled if p.DisableCustomSANs { if payload.Subject != doc.InstanceID && payload.Subject != doc.PrivateIP && payload.Subject != fmt.Sprintf("ip-%s.%s.compute.internal", strings.Replace(doc.PrivateIP, ".", "-", -1), doc.Region) { return nil, errs.Unauthorized("aws.authorizeToken; invalid token - invalid subject claim (sub)") } } // 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, errs.Unauthorized("aws.authorizeToken; invalid aws identity document - accountId is not valid") } } // validate instance age if d := p.InstanceAge.Value(); d > 0 { if now.Sub(doc.PendingTime) > d { return nil, errs.Unauthorized("aws.authorizeToken; aws identity document pendingTime is too old") } } payload.document = doc return &payload, nil } // AuthorizeSSHSign returns the list of SignOption for a SignSSH request. func (p *AWS) AuthorizeSSHSign(ctx context.Context, token string) ([]SignOption, error) { if !p.claimer.IsSSHCAEnabled() { return nil, errs.Unauthorized("aws.AuthorizeSSHSign; ssh ca is disabled for aws provisioner %s", p.GetID()) } claims, err := p.authorizeToken(token) if err != nil { return nil, errs.Wrap(http.StatusInternalServerError, err, "aws.AuthorizeSSHSign") } doc := claims.document signOptions := []SignOption{ // set the key id to the instance id sshCertKeyIDModifier(doc.InstanceID), } // Only enforce known principals if disable custom sans is true. var principals []string if p.DisableCustomSANs { principals = []string{ doc.PrivateIP, fmt.Sprintf("ip-%s.%s.compute.internal", strings.Replace(doc.PrivateIP, ".", "-", -1), doc.Region), } } // Default to cert type to host defaults := SSHOptions{ CertType: SSHHostCert, Principals: principals, } // Validate user options signOptions = append(signOptions, sshCertOptionsValidator(defaults)) // Set defaults if not given as user options signOptions = append(signOptions, sshCertDefaultsModifier(defaults)) return append(signOptions, // Set the default extensions. &sshDefaultExtensionModifier{}, // Set the validity bounds if not set. &sshDefaultDuration{p.claimer}, // Validate public key &sshDefaultPublicKeyValidator{}, // Validate the validity period. &sshCertValidityValidator{p.claimer}, // Require all the fields in the SSH certificate &sshCertDefaultValidator{}, ), nil }