package authority import ( "context" "crypto/rand" "crypto/x509" "encoding/binary" "errors" "fmt" "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" policy "github.com/smallstep/certificates/policy" "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 ; nc -q0 localhost 22" but it can be changed in the // configuration. The string "" will be replace by the new // principal to add. SSHAddUserCommand = "sudo useradd -m ; 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 ` 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 } } 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 { if _, ok := err.(*sshutil.TemplateError); ok { 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 pe *policy.NamePolicyError if errors.As(err, &pe) && pe.Reason == policy.NotAllowed { return nil, &errs.Error{ // NOTE: custom forbidden error, so that denied name is sent to client // as well as shown in the logs. Status: http.StatusForbidden, Err: fmt.Errorf("authority not allowed to sign: %w", err), Msg: fmt.Sprintf("The request was forbidden by the certificate authority: %s", err.Error()), } } 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 && 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 && 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 && 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 && 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 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) }