package provisioner import ( "crypto/rsa" "encoding/binary" "math/big" "time" "github.com/pkg/errors" "github.com/smallstep/cli/crypto/keys" "golang.org/x/crypto/ssh" ) const ( // SSHUserCert is the string used to represent ssh.UserCert. SSHUserCert = "user" // SSHHostCert is the string used to represent ssh.HostCert. SSHHostCert = "host" ) // SSHCertificateModifier is the interface used to change properties in an SSH // certificate. type SSHCertificateModifier interface { SignOption Modify(cert *ssh.Certificate) error } // SSHCertificateOptionModifier is the interface used to add custom options used // to modify the SSH certificate. type SSHCertificateOptionModifier interface { SignOption Option(o SSHOptions) SSHCertificateModifier } // SSHCertificateValidator is the interface used to validate an SSH certificate. type SSHCertificateValidator interface { SignOption Valid(cert *ssh.Certificate) error } // SSHCertificateOptionsValidator is the interface used to validate the custom // options used to modify the SSH certificate. type SSHCertificateOptionsValidator interface { SignOption Valid(got SSHOptions) error } // SSHOptions contains the options that can be passed to the SignSSH method. type SSHOptions struct { CertType string `json:"certType"` Principals []string `json:"principals"` ValidAfter TimeDuration `json:"validAfter,omitempty"` ValidBefore TimeDuration `json:"validBefore,omitempty"` } // Type returns the uint32 representation of the CertType. func (o SSHOptions) Type() uint32 { return sshCertTypeUInt32(o.CertType) } // Modify implements SSHCertificateModifier and sets the SSHOption in the ssh.Certificate. func (o SSHOptions) Modify(cert *ssh.Certificate) error { switch o.CertType { case "": // ignore case SSHUserCert: cert.CertType = ssh.UserCert case SSHHostCert: cert.CertType = ssh.HostCert default: return errors.Errorf("ssh certificate has an unknown type: %s", o.CertType) } cert.ValidPrincipals = o.Principals if !o.ValidAfter.IsZero() { cert.ValidAfter = uint64(o.ValidAfter.Time().Unix()) } if !o.ValidBefore.IsZero() { cert.ValidBefore = uint64(o.ValidBefore.Time().Unix()) } if cert.ValidAfter > 0 && cert.ValidBefore > 0 && cert.ValidAfter > cert.ValidBefore { return errors.New("ssh certificate valid after cannot be greater than valid before") } return nil } // match compares two SSHOptions and return an error if they don't match. It // ignores zero values. func (o SSHOptions) match(got SSHOptions) error { if o.CertType != "" && got.CertType != "" && o.CertType != got.CertType { return errors.Errorf("ssh certificate type does not match - got %v, want %v", got.CertType, o.CertType) } if len(o.Principals) > 0 && len(got.Principals) > 0 && !containsAllMembers(o.Principals, got.Principals) { return errors.Errorf("ssh certificate principals does not match - got %v, want %v", got.Principals, o.Principals) } if !o.ValidAfter.IsZero() && !got.ValidAfter.IsZero() && !o.ValidAfter.Equal(&got.ValidAfter) { return errors.Errorf("ssh certificate valid after does not match - got %v, want %v", got.ValidAfter, o.ValidAfter) } if !o.ValidBefore.IsZero() && !got.ValidBefore.IsZero() && !o.ValidBefore.Equal(&got.ValidBefore) { return errors.Errorf("ssh certificate valid before does not match - got %v, want %v", got.ValidBefore, o.ValidBefore) } return nil } // sshCertificateKeyIDModifier is an SSHCertificateModifier that sets the given // Key ID in the SSH certificate. type sshCertificateKeyIDModifier string func (m sshCertificateKeyIDModifier) Modify(cert *ssh.Certificate) error { cert.KeyId = string(m) return nil } // sshCertificateCertTypeModifier is an SSHCertificateModifier that sets the // certificate type to the SSH certificate. type sshCertificateCertTypeModifier string func (m sshCertificateCertTypeModifier) Modify(cert *ssh.Certificate) error { cert.CertType = sshCertTypeUInt32(string(m)) return nil } // sshCertificatePrincipalsModifier is an SSHCertificateModifier that sets the // principals to the SSH certificate. type sshCertificatePrincipalsModifier []string func (m sshCertificatePrincipalsModifier) Modify(cert *ssh.Certificate) error { cert.ValidPrincipals = []string(m) return nil } // sshCertificateValidAfterModifier is an SSHCertificateModifier that sets the // ValidAfter in the SSH certificate. type sshCertificateValidAfterModifier uint64 func (m sshCertificateValidAfterModifier) Modify(cert *ssh.Certificate) error { cert.ValidAfter = uint64(m) return nil } // sshCertificateValidBeforeModifier is an SSHCertificateModifier that sets the // ValidBefore in the SSH certificate. type sshCertificateValidBeforeModifier uint64 func (m sshCertificateValidBeforeModifier) Modify(cert *ssh.Certificate) error { cert.ValidBefore = uint64(m) return nil } // sshCertificateDefaultModifier implements a SSHCertificateModifier that // modifies the certificate with the given options if they are not set. type sshCertificateDefaultsModifier SSHOptions // Modify implements the SSHCertificateModifier interface. func (m sshCertificateDefaultsModifier) Modify(cert *ssh.Certificate) error { if cert.CertType == 0 { cert.CertType = sshCertTypeUInt32(m.CertType) } if len(cert.ValidPrincipals) == 0 { cert.ValidPrincipals = m.Principals } if cert.ValidAfter == 0 && !m.ValidAfter.IsZero() { cert.ValidAfter = uint64(m.ValidAfter.Unix()) } if cert.ValidBefore == 0 && !m.ValidBefore.IsZero() { cert.ValidBefore = uint64(m.ValidBefore.Unix()) } return nil } // sshDefaultExtensionModifier implements an SSHCertificateModifier that sets // the default extensions in an SSH certificate. type sshDefaultExtensionModifier struct{} func (m *sshDefaultExtensionModifier) Modify(cert *ssh.Certificate) error { switch cert.CertType { // Default to no extensions for HostCert. case ssh.HostCert: return nil case ssh.UserCert: if cert.Extensions == nil { cert.Extensions = make(map[string]string) } cert.Extensions["permit-X11-forwarding"] = "" cert.Extensions["permit-agent-forwarding"] = "" cert.Extensions["permit-port-forwarding"] = "" cert.Extensions["permit-pty"] = "" cert.Extensions["permit-user-rc"] = "" return nil default: return errors.New("ssh certificate type has not been set or is invalid") } } // sshValidityModifier is an SSHCertificateModifier that checks the // validity bounds, setting them if they are not provided. It will fail if a // CertType has not been set or is not valid. type sshValidityModifier struct { *Claimer validBefore time.Time } func (m *sshValidityModifier) Modify(cert *ssh.Certificate) error { var d time.Duration switch cert.CertType { case ssh.UserCert: d = m.DefaultUserSSHCertDuration() case ssh.HostCert: d = m.DefaultHostSSHCertDuration() case 0: return errors.New("ssh certificate type has not been set") default: return errors.Errorf("unknown ssh certificate type %d", cert.CertType) } hasLimit := !m.validBefore.IsZero() n := now() if cert.ValidAfter == 0 { cert.ValidAfter = uint64(n.Truncate(time.Second).Unix()) } certValidAfter := time.Unix(int64(cert.ValidAfter), 0) if hasLimit && certValidAfter.After(m.validBefore) { return errors.Errorf("provisioning credential expiration (%s) is before "+ "requested certificate validAfter (%s)", m.validBefore, certValidAfter) } if cert.ValidBefore == 0 { certValidBefore := certValidAfter.Add(d) if hasLimit && m.validBefore.Before(certValidBefore) { certValidBefore = m.validBefore } cert.ValidBefore = uint64(certValidBefore.Unix()) } else if hasLimit { certValidBefore := time.Unix(int64(cert.ValidBefore), 0) if m.validBefore.Before(certValidBefore) { return errors.Errorf("provisioning credential expiration (%s) is before "+ "requested certificate validBefore (%s)", m.validBefore, certValidBefore) } } return nil } func sshDefaultValidityModifier(c *Claimer) SSHCertificateModifier { return &sshValidityModifier{c, time.Time{}} } // sshLimitValidityModifier adjusts the duration to // min(default, remaining provisioning credential duration). // E.g. if the default is 12hrs but the remaining validity of the provisioning // credential is only 4hrs, this option will set the value to 4hrs (the min of the two values). func sshLimitValidityModifier(c *Claimer, validBefore time.Time) SSHCertificateModifier { return &sshValidityModifier{c, validBefore} } // sshCertificateOptionsValidator validates the user SSHOptions with the ones // usually present in the token. type sshCertificateOptionsValidator SSHOptions // Valid implements SSHCertificateOptionsValidator and returns nil if both // SSHOptions match. func (v sshCertificateOptionsValidator) Valid(got SSHOptions) error { want := SSHOptions(v) return want.match(got) } type sshCertificateValidityValidator struct { *Claimer } func (v *sshCertificateValidityValidator) Valid(cert *ssh.Certificate) error { switch { case cert.ValidAfter == 0: return errors.New("ssh certificate validAfter cannot be 0") case cert.ValidBefore < uint64(now().Unix()): return errors.New("ssh certificate validBefore cannot be in the past") case cert.ValidBefore < cert.ValidAfter: return errors.New("ssh certificate validBefore cannot be before validAfter") } var min, max time.Duration switch cert.CertType { case ssh.UserCert: min = v.MinUserSSHCertDuration() max = v.MaxUserSSHCertDuration() case ssh.HostCert: min = v.MinHostSSHCertDuration() max = v.MaxHostSSHCertDuration() case 0: return errors.New("ssh certificate type has not been set") default: return errors.Errorf("unknown ssh certificate type %d", cert.CertType) } // seconds dur := time.Duration(cert.ValidBefore-cert.ValidAfter) * time.Second switch { case dur < min: return errors.Errorf("requested duration of %s is less than minimum "+ "accepted duration for selected provisioner of %s", dur, min) case dur > max: return errors.Errorf("requested duration of %s is greater than maximum "+ "accepted duration for selected provisioner of %s", dur, max) default: return nil } } // sshCertificateDefaultValidator implements a simple validator for all the // fields in the SSH certificate. type sshCertificateDefaultValidator struct{} // Valid returns an error if the given certificate does not contain the necessary fields. func (v *sshCertificateDefaultValidator) Valid(cert *ssh.Certificate) error { switch { case len(cert.Nonce) == 0: return errors.New("ssh certificate nonce cannot be empty") case cert.Key == nil: return errors.New("ssh certificate key cannot be nil") case cert.Serial == 0: return errors.New("ssh certificate serial cannot be 0") case cert.CertType != ssh.UserCert && cert.CertType != ssh.HostCert: return errors.Errorf("ssh certificate has an unknown type: %d", cert.CertType) case cert.KeyId == "": return errors.New("ssh certificate key id cannot be empty") case len(cert.ValidPrincipals) == 0: return errors.New("ssh certificate valid principals cannot be empty") case cert.ValidAfter == 0: return errors.New("ssh certificate validAfter cannot be 0") case cert.ValidBefore < uint64(now().Unix()): return errors.New("ssh certificate validBefore cannot be in the past") case cert.ValidBefore < cert.ValidAfter: return errors.New("ssh certificate validBefore cannot be before validAfter") case cert.CertType == ssh.UserCert && len(cert.Extensions) == 0: return errors.New("ssh certificate extensions cannot be empty") case cert.SignatureKey == nil: return errors.New("ssh certificate signature key cannot be nil") case cert.Signature == nil: return errors.New("ssh certificate signature cannot be nil") default: return nil } } // sshDefaultPublicKeyValidator implements a validator for the certificate key. type sshDefaultPublicKeyValidator struct{} // Valid checks that certificate request common name matches the one configured. func (v sshDefaultPublicKeyValidator) Valid(cert *ssh.Certificate) error { if cert.Key == nil { return errors.New("ssh certificate key cannot be nil") } switch cert.Key.Type() { case ssh.KeyAlgoRSA: _, in, ok := sshParseString(cert.Key.Marshal()) if !ok { return errors.New("ssh certificate key is invalid") } key, err := sshParseRSAPublicKey(in) if err != nil { return err } if key.Size() < keys.MinRSAKeyBytes { return errors.Errorf("ssh certificate key must be at least %d bits (%d bytes)", 8*keys.MinRSAKeyBytes, keys.MinRSAKeyBytes) } return nil case ssh.KeyAlgoDSA: return errors.New("ssh certificate key algorithm (DSA) is not supported") default: return nil } } // sshCertTypeUInt32 func sshCertTypeUInt32(ct string) uint32 { switch ct { case SSHUserCert: return ssh.UserCert case SSHHostCert: return ssh.HostCert default: return 0 } } // containsAllMembers reports whether all members of subgroup are within group. func containsAllMembers(group, subgroup []string) bool { lg, lsg := len(group), len(subgroup) if lsg > lg || (lg > 0 && lsg == 0) { return false } visit := make(map[string]struct{}, lg) for i := 0; i < lg; i++ { visit[group[i]] = struct{}{} } for i := 0; i < lsg; i++ { if _, ok := visit[subgroup[i]]; !ok { return false } } return true } func sshParseString(in []byte) (out, rest []byte, ok bool) { if len(in) < 4 { return } length := binary.BigEndian.Uint32(in) in = in[4:] if uint32(len(in)) < length { return } out = in[:length] rest = in[length:] ok = true return } func sshParseRSAPublicKey(in []byte) (*rsa.PublicKey, error) { var w struct { E *big.Int N *big.Int Rest []byte `ssh:"rest"` } if err := ssh.Unmarshal(in, &w); err != nil { return nil, errors.Wrap(err, "error unmarshalling public key") } if w.E.BitLen() > 24 { return nil, errors.New("invalid public key: exponent too large") } e := w.E.Int64() if e < 3 || e&1 == 0 { return nil, errors.New("invalid public key: incorrect exponent") } var key rsa.PublicKey key.E = int(e) key.N = w.N return &key, nil }