certificates/authority/ssh.go

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package authority
import (
"context"
"crypto/rand"
"crypto/x509"
"encoding/binary"
"net/http"
"strings"
"time"
"github.com/pkg/errors"
"github.com/smallstep/certificates/authority/provisioner"
"github.com/smallstep/certificates/db"
"github.com/smallstep/certificates/errs"
"github.com/smallstep/certificates/sshutil"
"github.com/smallstep/certificates/templates"
"github.com/smallstep/cli/crypto/randutil"
"github.com/smallstep/cli/jose"
"golang.org/x/crypto/ssh"
)
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"
)
// SSHConfig contains the user and host keys.
type SSHConfig struct {
HostKey string `json:"hostKey"`
UserKey string `json:"userKey"`
Keys []*SSHPublicKey `json:"keys,omitempty"`
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AddUserPrincipal string `json:"addUserPrincipal,omitempty"`
AddUserCommand string `json:"addUserCommand,omitempty"`
Bastion *Bastion `json:"bastion,omitempty"`
}
// Bastion contains the custom properties used on bastion.
type Bastion struct {
Hostname string `json:"hostname"`
User string `json:"user,omitempty"`
Port string `json:"port,omitempty"`
Command string `json:"cmd,omitempty"`
Flags string `json:"flags,omitempty"`
}
// Validate checks the fields in SSHConfig.
func (c *SSHConfig) Validate() error {
if c == nil {
return nil
}
for _, k := range c.Keys {
if err := k.Validate(); err != nil {
return err
}
}
return nil
}
// SSHPublicKey contains a public key used by federated CAs to keep old signing
// keys for this ca.
type SSHPublicKey struct {
Type string `json:"type"`
Federated bool `json:"federated"`
Key jose.JSONWebKey `json:"key"`
publicKey ssh.PublicKey
}
// Validate checks the fields in SSHPublicKey.
func (k *SSHPublicKey) Validate() error {
switch {
case k.Type == "":
return errors.New("type cannot be empty")
case k.Type != provisioner.SSHHostCert && k.Type != provisioner.SSHUserCert:
return errors.Errorf("invalid type %s, it must be user or host", k.Type)
case !k.Key.IsPublic():
return errors.New("invalid key type, it must be a public key")
}
key, err := ssh.NewPublicKey(k.Key.Key)
if err != nil {
return errors.Wrap(err, "error creating ssh key")
}
k.publicKey = key
return nil
}
// PublicKey returns the ssh public key.
func (k *SSHPublicKey) PublicKey() ssh.PublicKey {
return k.publicKey
}
// SSHKeys represents the SSH User and Host public keys.
type SSHKeys struct {
UserKeys []ssh.PublicKey
HostKeys []ssh.PublicKey
}
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// GetSSHRoots returns the SSH User and Host public keys.
func (a *Authority) GetSSHRoots(context.Context) (*SSHKeys, error) {
return &SSHKeys{
HostKeys: a.sshCAHostCerts,
UserKeys: a.sshCAUserCerts,
}, nil
}
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// GetSSHFederation returns the public keys for federated SSH signers.
func (a *Authority) GetSSHFederation(context.Context) (*SSHKeys, error) {
return &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 {
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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:
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return nil, errs.BadRequest("getSSHConfig: type %s is not valid", 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, errs.WithMessage("%v, please use `--set <key=value>` flag", err))
}
o, err := t.Output(mergedData)
if err != nil {
return nil, err
}
output = append(output, o)
}
return output, nil
}
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// GetSSHBastion returns the bastion configuration, for the given pair user,
// hostname.
func (a *Authority) GetSSHBastion(ctx context.Context, user string, hostname string) (*Bastion, error) {
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if a.sshBastionFunc != nil {
bs, err := a.sshBastionFunc(ctx, user, hostname)
return bs, errs.Wrap(http.StatusInternalServerError, err, "authority.GetSSHBastion")
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}
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
}
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}
return nil, nil
}
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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) {
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var mods []provisioner.SSHCertModifier
var validators []provisioner.SSHCertValidator
// Set backdate with the configured value
opts.Backdate = a.config.AuthorityConfig.Backdate.Duration
for _, op := range signOpts {
switch o := op.(type) {
// modify the ssh.Certificate
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case provisioner.SSHCertModifier:
mods = append(mods, o)
// modify the ssh.Certificate given the SSHOptions
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case provisioner.SSHCertOptionModifier:
mods = append(mods, o.Option(opts))
// validate the ssh.Certificate
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case provisioner.SSHCertValidator:
validators = append(validators, o)
// validate the given SSHOptions
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case provisioner.SSHCertOptionsValidator:
if err := o.Valid(opts); err != nil {
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return nil, errs.Wrap(http.StatusForbidden, err, "signSSH")
}
default:
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return nil, errs.InternalServer("signSSH: invalid extra option type %T", o)
}
}
nonce, err := randutil.ASCII(32)
if err != nil {
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return nil, errs.Wrap(http.StatusInternalServerError, err, "signSSH")
}
var serial uint64
if err := binary.Read(rand.Reader, binary.BigEndian, &serial); err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "signSSH: error reading random number")
}
// Build base certificate with the key and some random values
cert := &ssh.Certificate{
Nonce: []byte(nonce),
Key: key,
Serial: serial,
}
// Use opts to modify the certificate
if err := opts.Modify(cert); err != nil {
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return nil, errs.Wrap(http.StatusForbidden, err, "signSSH")
}
// Use provisioner modifiers
for _, m := range mods {
if err := m.Modify(cert); err != nil {
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return nil, errs.Wrap(http.StatusForbidden, err, "signSSH")
}
}
// Get signer from authority keys
var signer ssh.Signer
switch cert.CertType {
case ssh.UserCert:
if a.sshCAUserCertSignKey == nil {
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return nil, errs.NotImplemented("signSSH: user certificate signing is not enabled")
}
signer = a.sshCAUserCertSignKey
case ssh.HostCert:
if a.sshCAHostCertSignKey == nil {
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return nil, errs.NotImplemented("signSSH: host certificate signing is not enabled")
}
signer = a.sshCAHostCertSignKey
default:
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return nil, errs.InternalServer("signSSH: unexpected ssh certificate type: %d", cert.CertType)
}
cert.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, errs.Wrap(http.StatusInternalServerError, err, "signSSH: error signing certificate")
}
cert.Signature = sig
// User provisioners validators
for _, v := range validators {
if err := v.Valid(cert, opts); err != nil {
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return nil, errs.Wrap(http.StatusForbidden, err, "signSSH")
}
}
if err = a.db.StoreSSHCertificate(cert); err != nil && err != db.ErrNotImplemented {
return nil, errs.Wrap(http.StatusInternalServerError, err, "signSSH: error storing certificate in db")
}
return cert, nil
}
// 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) {
nonce, err := randutil.ASCII(32)
if err != nil {
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return nil, errs.Wrap(http.StatusInternalServerError, err, "renewSSH")
}
var serial uint64
if err := binary.Read(rand.Reader, binary.BigEndian, &serial); err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "renewSSH: error reading random number")
}
if oldCert.ValidAfter == 0 || oldCert.ValidBefore == 0 {
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return nil, errs.BadRequest("rewnewSSH: cannot renew certificate without validity period")
}
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 key and some random values
cert := &ssh.Certificate{
Nonce: []byte(nonce),
Key: oldCert.Key,
Serial: serial,
CertType: oldCert.CertType,
KeyId: oldCert.KeyId,
ValidPrincipals: oldCert.ValidPrincipals,
Permissions: oldCert.Permissions,
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 {
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return nil, errs.NotImplemented("renewSSH: user certificate signing is not enabled")
}
signer = a.sshCAUserCertSignKey
case ssh.HostCert:
if a.sshCAHostCertSignKey == nil {
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return nil, errs.NotImplemented("renewSSH: host certificate signing is not enabled")
}
signer = a.sshCAHostCertSignKey
default:
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return nil, errs.InternalServer("renewSSH: unexpected ssh certificate type: %d", cert.CertType)
}
cert.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, errs.Wrap(http.StatusInternalServerError, err, "renewSSH: error signing certificate")
}
cert.Signature = sig
if err = a.db.StoreSSHCertificate(cert); err != nil && 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) {
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var validators []provisioner.SSHCertValidator
for _, op := range signOpts {
switch o := op.(type) {
// validate the ssh.Certificate
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case provisioner.SSHCertValidator:
validators = append(validators, o)
default:
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return nil, errs.InternalServer("rekeySSH; invalid extra option type %T", o)
}
}
nonce, err := randutil.ASCII(32)
if err != nil {
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return nil, errs.Wrap(http.StatusInternalServerError, err, "rekeySSH")
}
var serial uint64
if err := binary.Read(rand.Reader, binary.BigEndian, &serial); err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "rekeySSH; error reading random number")
}
if oldCert.ValidAfter == 0 || oldCert.ValidBefore == 0 {
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return nil, errs.BadRequest("rekeySSH; cannot rekey certificate without validity period")
}
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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 key and some random values
cert := &ssh.Certificate{
Nonce: []byte(nonce),
Key: pub,
Serial: serial,
CertType: oldCert.CertType,
KeyId: oldCert.KeyId,
ValidPrincipals: oldCert.ValidPrincipals,
Permissions: oldCert.Permissions,
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 {
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return nil, errs.NotImplemented("rekeySSH; user certificate signing is not enabled")
}
signer = a.sshCAUserCertSignKey
case ssh.HostCert:
if a.sshCAHostCertSignKey == nil {
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return nil, errs.NotImplemented("rekeySSH; host certificate signing is not enabled")
}
signer = a.sshCAHostCertSignKey
default:
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return nil, errs.BadRequest("rekeySSH; unexpected ssh certificate type: %d", cert.CertType)
}
cert.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, errs.Wrap(http.StatusInternalServerError, err, "rekeySSH; error signing certificate")
}
cert.Signature = sig
// Apply validators from provisioner.
for _, v := range validators {
if err := v.Valid(cert, provisioner.SignSSHOptions{Backdate: backdate}); err != nil {
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return nil, errs.Wrap(http.StatusForbidden, err, "rekeySSH")
}
}
if err = a.db.StoreSSHCertificate(cert); err != nil && err != db.ErrNotImplemented {
return nil, errs.Wrap(http.StatusInternalServerError, err, "rekeySSH; error storing certificate in db")
}
return cert, 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 errors.New("certificate is not a user certificate")
}
switch len(cert.ValidPrincipals) {
case 0:
return errors.New("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 errors.New("certificate does not have only one principal")
default:
return errors.New("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 {
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return nil, errs.NotImplemented("signSSHAddUser: user certificate signing is not enabled")
}
if err := IsValidForAddUser(subject); err != nil {
return nil, errs.Wrap(http.StatusForbidden, err, "signSSHAddUser")
}
nonce, err := randutil.ASCII(32)
if err != nil {
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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")
}
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.db.StoreSSHCertificate(cert); err != nil && 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 string, 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 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
}
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// GetSSHHosts returns a list of valid host principals.
func (a *Authority) GetSSHHosts(ctx context.Context, cert *x509.Certificate) ([]sshutil.Host, error) {
if a.sshGetHostsFunc != nil {
hosts, err := a.sshGetHostsFunc(ctx, cert)
return hosts, errs.Wrap(http.StatusInternalServerError, err, "getSSHHosts")
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}
hostnames, err := a.db.GetSSHHostPrincipals()
if err != nil {
return nil, errs.Wrap(http.StatusInternalServerError, err, "getSSHHosts")
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}
hosts := make([]sshutil.Host, len(hostnames))
for i, hn := range hostnames {
hosts[i] = sshutil.Host{Hostname: hn}
}
return hosts, nil
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}
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.Replace(cmd, "<principal>", principal, -1)
}