certificates/authority/ssh.go
2022-09-21 18:35:18 -07:00

633 lines
20 KiB
Go

package authority
import (
"context"
"crypto/rand"
"crypto/x509"
"encoding/binary"
"errors"
"net/http"
"strings"
"time"
"golang.org/x/crypto/ssh"
"go.step.sm/crypto/randutil"
"go.step.sm/crypto/sshutil"
"github.com/smallstep/certificates/authority/config"
"github.com/smallstep/certificates/authority/provisioner"
"github.com/smallstep/certificates/db"
"github.com/smallstep/certificates/errs"
"github.com/smallstep/certificates/templates"
)
const (
// SSHAddUserPrincipal is the principal that will run the add user command.
// Defaults to "provisioner" but it can be changed in the configuration.
SSHAddUserPrincipal = "provisioner"
// SSHAddUserCommand is the default command to run to add a new user.
// Defaults to "sudo useradd -m <principal>; nc -q0 localhost 22" but it can be changed in the
// configuration. The string "<principal>" will be replace by the new
// principal to add.
SSHAddUserCommand = "sudo useradd -m <principal>; nc -q0 localhost 22"
)
// GetSSHRoots returns the SSH User and Host public keys.
func (a *Authority) GetSSHRoots(context.Context) (*config.SSHKeys, error) {
return &config.SSHKeys{
HostKeys: a.sshCAHostCerts,
UserKeys: a.sshCAUserCerts,
}, nil
}
// GetSSHFederation returns the public keys for federated SSH signers.
func (a *Authority) GetSSHFederation(context.Context) (*config.SSHKeys, error) {
return &config.SSHKeys{
HostKeys: a.sshCAHostFederatedCerts,
UserKeys: a.sshCAUserFederatedCerts,
}, nil
}
// GetSSHConfig returns rendered templates for clients (user) or servers (host).
func (a *Authority) GetSSHConfig(ctx context.Context, typ string, data map[string]string) ([]templates.Output, error) {
if a.sshCAUserCertSignKey == nil && a.sshCAHostCertSignKey == nil {
return nil, errs.NotFound("getSSHConfig: ssh is not configured")
}
if a.templates == nil {
return nil, errs.NotFound("getSSHConfig: ssh templates are not configured")
}
var ts []templates.Template
switch typ {
case provisioner.SSHUserCert:
if a.templates != nil && a.templates.SSH != nil {
ts = a.templates.SSH.User
}
case provisioner.SSHHostCert:
if a.templates != nil && a.templates.SSH != nil {
ts = a.templates.SSH.Host
}
default:
return nil, errs.BadRequest("invalid certificate type '%s'", typ)
}
// Merge user and default data
var mergedData map[string]interface{}
if len(data) == 0 {
mergedData = a.templates.Data
} else {
mergedData = make(map[string]interface{}, len(a.templates.Data)+1)
mergedData["User"] = data
for k, v := range a.templates.Data {
mergedData[k] = v
}
}
// Render templates
output := []templates.Output{}
for _, t := range ts {
if err := t.Load(); err != nil {
return nil, err
}
// Check for required variables.
if err := t.ValidateRequiredData(data); err != nil {
return nil, errs.BadRequestErr(err, "%v, please use `--set <key=value>` flag", err)
}
o, err := t.Output(mergedData)
if err != nil {
return nil, err
}
// Backwards compatibility for version of the cli older than v0.18.0.
// Before v0.18.0 we were not passing any value for SSHTemplateVersionKey
// from the cli.
if o.Name == "step_includes.tpl" && data[templates.SSHTemplateVersionKey] == "" {
o.Type = templates.File
o.Path = strings.TrimPrefix(o.Path, "${STEPPATH}/")
}
output = append(output, o)
}
return output, nil
}
// GetSSHBastion returns the bastion configuration, for the given pair user,
// hostname.
func (a *Authority) GetSSHBastion(ctx context.Context, user, hostname string) (*config.Bastion, error) {
if a.sshBastionFunc != nil {
bs, err := a.sshBastionFunc(ctx, user, hostname)
return bs, errs.Wrap(http.StatusInternalServerError, err, "authority.GetSSHBastion")
}
if a.config.SSH != nil {
if a.config.SSH.Bastion != nil && a.config.SSH.Bastion.Hostname != "" {
// Do not return a bastion for a bastion host.
//
// This condition might fail if a different name or IP is used.
// Trying to resolve hostnames to IPs and compare them won't be a
// complete solution because it depends on the network
// configuration, of the CA and clients and can also return false
// positives. Although not perfect, this simple solution will work
// in most cases.
if !strings.EqualFold(hostname, a.config.SSH.Bastion.Hostname) {
return a.config.SSH.Bastion, nil
}
}
//nolint:nilnil // legacy
return nil, nil
}
return nil, errs.NotFound("authority.GetSSHBastion; ssh is not configured")
}
// SignSSH creates a signed SSH certificate with the given public key and options.
func (a *Authority) SignSSH(ctx context.Context, key ssh.PublicKey, opts provisioner.SignSSHOptions, signOpts ...provisioner.SignOption) (*ssh.Certificate, error) {
var (
certOptions []sshutil.Option
mods []provisioner.SSHCertModifier
validators []provisioner.SSHCertValidator
)
// Validate given options.
if err := opts.Validate(); err != nil {
return nil, err
}
// Set backdate with the configured value
opts.Backdate = a.config.AuthorityConfig.Backdate.Duration
var prov provisioner.Interface
for _, op := range signOpts {
switch o := op.(type) {
// Capture current provisioner
case provisioner.Interface:
prov = o
// add options to NewCertificate
case provisioner.SSHCertificateOptions:
certOptions = append(certOptions, o.Options(opts)...)
// modify the ssh.Certificate
case provisioner.SSHCertModifier:
mods = append(mods, o)
// validate the ssh.Certificate
case provisioner.SSHCertValidator:
validators = append(validators, o)
// validate the given SSHOptions
case provisioner.SSHCertOptionsValidator:
if err := o.Valid(opts); err != nil {
return nil, errs.BadRequestErr(err, "error validating ssh certificate options")
}
default:
return nil, errs.InternalServer("authority.SignSSH: invalid extra option type %T", o)
}
}
// Simulated certificate request with request options.
cr := sshutil.CertificateRequest{
Type: opts.CertType,
KeyID: opts.KeyID,
Principals: opts.Principals,
Key: key,
}
// Create certificate from template.
certificate, err := sshutil.NewCertificate(cr, certOptions...)
if err != nil {
var te *sshutil.TemplateError
if errors.As(err, &te) {
return nil, errs.ApplyOptions(
errs.BadRequestErr(err, err.Error()),
errs.WithKeyVal("signOptions", signOpts),
)
}
// explicitly check for unmarshaling errors, which are most probably caused by JSON template syntax errors
if strings.HasPrefix(err.Error(), "error unmarshaling certificate") {
return nil, errs.InternalServerErr(templatingError(err),
errs.WithKeyVal("signOptions", signOpts),
errs.WithMessage("error applying certificate template"),
)
}
return nil, errs.Wrap(http.StatusInternalServerError, err, "authority.SignSSH")
}
// Get actual *ssh.Certificate and continue with provisioner modifiers.
certTpl := certificate.GetCertificate()
// Use SignSSHOptions to modify the certificate validity. It will be later
// checked or set if not defined.
if err := opts.ModifyValidity(certTpl); err != nil {
return nil, errs.BadRequestErr(err, err.Error())
}
// Use provisioner modifiers.
for _, m := range mods {
if err := m.Modify(certTpl, opts); err != nil {
return nil, errs.ForbiddenErr(err, "error creating ssh certificate")
}
}
// Get signer from authority keys
var signer ssh.Signer
switch certTpl.CertType {
case ssh.UserCert:
if a.sshCAUserCertSignKey == nil {
return nil, errs.NotImplemented("authority.SignSSH: user certificate signing is not enabled")
}
signer = a.sshCAUserCertSignKey
case ssh.HostCert:
if a.sshCAHostCertSignKey == nil {
return nil, errs.NotImplemented("authority.SignSSH: host certificate signing is not enabled")
}
signer = a.sshCAHostCertSignKey
default:
return nil, errs.InternalServer("authority.SignSSH: unexpected ssh certificate type: %d", certTpl.CertType)
}
// Check if authority is allowed to sign the certificate
if err := a.isAllowedToSignSSHCertificate(certTpl); err != nil {
var ee *errs.Error
if errors.As(err, &ee) {
return nil, ee
}
return nil, errs.InternalServerErr(err,
errs.WithMessage("authority.SignSSH: error creating ssh certificate"),
)
}
// Sign certificate.
cert, err := sshutil.CreateCertificate(certTpl, signer)
if err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "authority.SignSSH: error signing certificate")
}
// User provisioners validators.
for _, v := range validators {
if err := v.Valid(cert, opts); err != nil {
return nil, errs.ForbiddenErr(err, "error validating ssh certificate")
}
}
if err = a.storeSSHCertificate(prov, cert); err != nil && !errors.Is(err, db.ErrNotImplemented) {
return nil, errs.Wrap(http.StatusInternalServerError, err, "authority.SignSSH: error storing certificate in db")
}
return cert, nil
}
// isAllowedToSignSSHCertificate checks if the Authority is allowed to sign the SSH certificate.
func (a *Authority) isAllowedToSignSSHCertificate(cert *ssh.Certificate) error {
return a.policyEngine.IsSSHCertificateAllowed(cert)
}
// RenewSSH creates a signed SSH certificate using the old SSH certificate as a template.
func (a *Authority) RenewSSH(ctx context.Context, oldCert *ssh.Certificate) (*ssh.Certificate, error) {
if oldCert.ValidAfter == 0 || oldCert.ValidBefore == 0 {
return nil, errs.BadRequest("cannot renew a certificate without validity period")
}
if err := a.authorizeSSHCertificate(ctx, oldCert); err != nil {
return nil, err
}
// Attempt to extract the provisioner from the token.
var prov provisioner.Interface
if token, ok := provisioner.TokenFromContext(ctx); ok {
prov, _, _ = a.getProvisionerFromToken(token)
}
backdate := a.config.AuthorityConfig.Backdate.Duration
duration := time.Duration(oldCert.ValidBefore-oldCert.ValidAfter) * time.Second
now := time.Now()
va := now.Add(-1 * backdate)
vb := now.Add(duration - backdate)
// Build base certificate with the old key.
// Nonce and serial will be automatically generated on signing.
certTpl := &ssh.Certificate{
Key: oldCert.Key,
CertType: oldCert.CertType,
KeyId: oldCert.KeyId,
ValidPrincipals: oldCert.ValidPrincipals,
Permissions: oldCert.Permissions,
Reserved: oldCert.Reserved,
ValidAfter: uint64(va.Unix()),
ValidBefore: uint64(vb.Unix()),
}
// Get signer from authority keys
var signer ssh.Signer
switch certTpl.CertType {
case ssh.UserCert:
if a.sshCAUserCertSignKey == nil {
return nil, errs.NotImplemented("renewSSH: user certificate signing is not enabled")
}
signer = a.sshCAUserCertSignKey
case ssh.HostCert:
if a.sshCAHostCertSignKey == nil {
return nil, errs.NotImplemented("renewSSH: host certificate signing is not enabled")
}
signer = a.sshCAHostCertSignKey
default:
return nil, errs.InternalServer("renewSSH: unexpected ssh certificate type: %d", certTpl.CertType)
}
// Sign certificate.
cert, err := sshutil.CreateCertificate(certTpl, signer)
if err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "signSSH: error signing certificate")
}
if err = a.storeRenewedSSHCertificate(prov, oldCert, cert); err != nil && !errors.Is(err, db.ErrNotImplemented) {
return nil, errs.Wrap(http.StatusInternalServerError, err, "renewSSH: error storing certificate in db")
}
return cert, nil
}
// RekeySSH creates a signed SSH certificate using the old SSH certificate as a template.
func (a *Authority) RekeySSH(ctx context.Context, oldCert *ssh.Certificate, pub ssh.PublicKey, signOpts ...provisioner.SignOption) (*ssh.Certificate, error) {
var validators []provisioner.SSHCertValidator
var prov provisioner.Interface
for _, op := range signOpts {
switch o := op.(type) {
// Capture current provisioner
case provisioner.Interface:
prov = o
// validate the ssh.Certificate
case provisioner.SSHCertValidator:
validators = append(validators, o)
default:
return nil, errs.InternalServer("rekeySSH; invalid extra option type %T", o)
}
}
if oldCert.ValidAfter == 0 || oldCert.ValidBefore == 0 {
return nil, errs.BadRequest("cannot rekey a certificate without validity period")
}
if err := a.authorizeSSHCertificate(ctx, oldCert); err != nil {
return nil, err
}
backdate := a.config.AuthorityConfig.Backdate.Duration
duration := time.Duration(oldCert.ValidBefore-oldCert.ValidAfter) * time.Second
now := time.Now()
va := now.Add(-1 * backdate)
vb := now.Add(duration - backdate)
// Build base certificate with the new key.
// Nonce and serial will be automatically generated on signing.
cert := &ssh.Certificate{
Key: pub,
CertType: oldCert.CertType,
KeyId: oldCert.KeyId,
ValidPrincipals: oldCert.ValidPrincipals,
Permissions: oldCert.Permissions,
Reserved: oldCert.Reserved,
ValidAfter: uint64(va.Unix()),
ValidBefore: uint64(vb.Unix()),
}
// Get signer from authority keys
var signer ssh.Signer
switch cert.CertType {
case ssh.UserCert:
if a.sshCAUserCertSignKey == nil {
return nil, errs.NotImplemented("rekeySSH; user certificate signing is not enabled")
}
signer = a.sshCAUserCertSignKey
case ssh.HostCert:
if a.sshCAHostCertSignKey == nil {
return nil, errs.NotImplemented("rekeySSH; host certificate signing is not enabled")
}
signer = a.sshCAHostCertSignKey
default:
return nil, errs.BadRequest("unexpected certificate type '%d'", cert.CertType)
}
var err error
// Sign certificate.
cert, err = sshutil.CreateCertificate(cert, signer)
if err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "signSSH: error signing certificate")
}
// Apply validators from provisioner.
for _, v := range validators {
if err := v.Valid(cert, provisioner.SignSSHOptions{Backdate: backdate}); err != nil {
return nil, errs.ForbiddenErr(err, "error validating ssh certificate")
}
}
if err = a.storeRenewedSSHCertificate(prov, oldCert, cert); err != nil && !errors.Is(err, db.ErrNotImplemented) {
return nil, errs.Wrap(http.StatusInternalServerError, err, "rekeySSH; error storing certificate in db")
}
return cert, nil
}
func (a *Authority) storeSSHCertificate(prov provisioner.Interface, cert *ssh.Certificate) error {
type sshCertificateStorer interface {
StoreSSHCertificate(provisioner.Interface, *ssh.Certificate) error
}
// Store certificate in admindb or linkedca
switch s := a.adminDB.(type) {
case sshCertificateStorer:
return s.StoreSSHCertificate(prov, cert)
case db.CertificateStorer:
return s.StoreSSHCertificate(cert)
}
// Store certificate in localdb
switch s := a.db.(type) {
case sshCertificateStorer:
return s.StoreSSHCertificate(prov, cert)
case db.CertificateStorer:
return s.StoreSSHCertificate(cert)
default:
return nil
}
}
func (a *Authority) storeRenewedSSHCertificate(prov provisioner.Interface, parent, cert *ssh.Certificate) error {
type sshRenewerCertificateStorer interface {
StoreRenewedSSHCertificate(p provisioner.Interface, parent, cert *ssh.Certificate) error
}
// Store certificate in admindb or linkedca
switch s := a.adminDB.(type) {
case sshRenewerCertificateStorer:
return s.StoreRenewedSSHCertificate(prov, parent, cert)
case db.CertificateStorer:
return s.StoreSSHCertificate(cert)
}
// Store certificate in localdb
switch s := a.db.(type) {
case sshRenewerCertificateStorer:
return s.StoreRenewedSSHCertificate(prov, parent, cert)
case db.CertificateStorer:
return s.StoreSSHCertificate(cert)
default:
return nil
}
}
// IsValidForAddUser checks if a user provisioner certificate can be issued to
// the given certificate.
func IsValidForAddUser(cert *ssh.Certificate) error {
if cert.CertType != ssh.UserCert {
return errs.Forbidden("certificate is not a user certificate")
}
switch len(cert.ValidPrincipals) {
case 0:
return errs.Forbidden("certificate does not have any principals")
case 1:
return nil
case 2:
// OIDC provisioners adds a second principal with the email address.
// @ cannot be the first character.
if strings.Index(cert.ValidPrincipals[1], "@") > 0 {
return nil
}
return errs.Forbidden("certificate does not have only one principal")
default:
return errs.Forbidden("certificate does not have only one principal")
}
}
// SignSSHAddUser signs a certificate that provisions a new user in a server.
func (a *Authority) SignSSHAddUser(ctx context.Context, key ssh.PublicKey, subject *ssh.Certificate) (*ssh.Certificate, error) {
if a.sshCAUserCertSignKey == nil {
return nil, errs.NotImplemented("signSSHAddUser: user certificate signing is not enabled")
}
if err := IsValidForAddUser(subject); err != nil {
return nil, err
}
nonce, err := randutil.ASCII(32)
if err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "signSSHAddUser")
}
var serial uint64
if err := binary.Read(rand.Reader, binary.BigEndian, &serial); err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "signSSHAddUser: error reading random number")
}
// Attempt to extract the provisioner from the token.
var prov provisioner.Interface
if token, ok := provisioner.TokenFromContext(ctx); ok {
prov, _, _ = a.getProvisionerFromToken(token)
}
signer := a.sshCAUserCertSignKey
principal := subject.ValidPrincipals[0]
addUserPrincipal := a.getAddUserPrincipal()
cert := &ssh.Certificate{
Nonce: []byte(nonce),
Key: key,
Serial: serial,
CertType: ssh.UserCert,
KeyId: principal + "-" + addUserPrincipal,
ValidPrincipals: []string{addUserPrincipal},
ValidAfter: subject.ValidAfter,
ValidBefore: subject.ValidBefore,
Permissions: ssh.Permissions{
CriticalOptions: map[string]string{
"force-command": a.getAddUserCommand(principal),
},
},
SignatureKey: signer.PublicKey(),
}
// Get bytes for signing trailing the signature length.
data := cert.Marshal()
data = data[:len(data)-4]
// Sign the certificate
sig, err := signer.Sign(rand.Reader, data)
if err != nil {
return nil, err
}
cert.Signature = sig
if err = a.storeRenewedSSHCertificate(prov, subject, cert); err != nil && !errors.Is(err, db.ErrNotImplemented) {
return nil, errs.Wrap(http.StatusInternalServerError, err, "signSSHAddUser: error storing certificate in db")
}
return cert, nil
}
// CheckSSHHost checks the given principal has been registered before.
func (a *Authority) CheckSSHHost(ctx context.Context, principal, token string) (bool, error) {
if a.sshCheckHostFunc != nil {
exists, err := a.sshCheckHostFunc(ctx, principal, token, a.GetRootCertificates())
if err != nil {
return false, errs.Wrap(http.StatusInternalServerError, err,
"checkSSHHost: error from injected checkSSHHost func")
}
return exists, nil
}
exists, err := a.db.IsSSHHost(principal)
if err != nil {
if errors.Is(err, db.ErrNotImplemented) {
return false, errs.Wrap(http.StatusNotImplemented, err,
"checkSSHHost: isSSHHost is not implemented")
}
return false, errs.Wrap(http.StatusInternalServerError, err,
"checkSSHHost: error checking if hosts exists")
}
return exists, nil
}
// GetSSHHosts returns a list of valid host principals.
func (a *Authority) GetSSHHosts(ctx context.Context, cert *x509.Certificate) ([]config.Host, error) {
if a.GetConfig().AuthorityConfig.DisableGetSSHHosts {
return nil, errs.New(http.StatusNotFound, "ssh hosts list api disabled")
}
if a.sshGetHostsFunc != nil {
hosts, err := a.sshGetHostsFunc(ctx, cert)
return hosts, errs.Wrap(http.StatusInternalServerError, err, "getSSHHosts")
}
hostnames, err := a.db.GetSSHHostPrincipals()
if err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "getSSHHosts")
}
hosts := make([]config.Host, len(hostnames))
for i, hn := range hostnames {
hosts[i] = config.Host{Hostname: hn}
}
return hosts, nil
}
func (a *Authority) getAddUserPrincipal() (cmd string) {
if a.config.SSH.AddUserPrincipal == "" {
return SSHAddUserPrincipal
}
return a.config.SSH.AddUserPrincipal
}
func (a *Authority) getAddUserCommand(principal string) string {
var cmd string
if a.config.SSH.AddUserCommand == "" {
cmd = SSHAddUserCommand
} else {
cmd = a.config.SSH.AddUserCommand
}
return strings.ReplaceAll(cmd, "<principal>", principal)
}