certificates/policy/engine.go
2022-09-21 18:35:18 -07:00

315 lines
10 KiB
Go
Executable file

package policy
import (
"crypto/x509"
"fmt"
"net"
"net/http"
"net/url"
"go.step.sm/crypto/x509util"
"golang.org/x/crypto/ssh"
"github.com/smallstep/certificates/errs"
)
type NamePolicyReason int
const (
// NotAllowed results when an instance of NamePolicyEngine
// determines that there's a constraint which doesn't permit
// a DNS or another type of SAN to be signed (or otherwise used).
NotAllowed NamePolicyReason = iota + 1
// CannotParseDomain is returned when an error occurs
// when parsing the domain part of SAN or subject.
CannotParseDomain
// CannotParseRFC822Name is returned when an error
// occurs when parsing an email address.
CannotParseRFC822Name
// CannotMatch is the type of error returned when
// an error happens when matching SAN types.
CannotMatchNameToConstraint
)
type NameType string
const (
CNNameType NameType = "cn"
DNSNameType NameType = "dns"
IPNameType NameType = "ip"
EmailNameType NameType = "email"
URINameType NameType = "uri"
PrincipalNameType NameType = "principal"
)
type NamePolicyError struct {
Reason NamePolicyReason
NameType NameType
Name string
detail string
}
func (e *NamePolicyError) Error() string {
switch e.Reason {
case NotAllowed:
return fmt.Sprintf("%s name %q not allowed", e.NameType, e.Name)
case CannotParseDomain:
return fmt.Sprintf("cannot parse %s domain %q", e.NameType, e.Name)
case CannotParseRFC822Name:
return fmt.Sprintf("cannot parse %s rfc822Name %q", e.NameType, e.Name)
case CannotMatchNameToConstraint:
return fmt.Sprintf("error matching %s name %q to constraint", e.NameType, e.Name)
default:
return fmt.Sprintf("unknown error reason (%d): %s", e.Reason, e.detail)
}
}
// As implements the As(any) bool interface and allows to use "errors.As()" to
// convert a NotAllowed NamePolicyError to an errs.Error.
func (e *NamePolicyError) As(v any) bool {
if e.Reason == NotAllowed {
if err, ok := v.(**errs.Error); ok {
*err = &errs.Error{
Status: http.StatusForbidden,
Msg: fmt.Sprintf("The request was forbidden by the certificate authority: %s", e.Error()),
Err: e,
}
return true
}
}
return false
}
func (e *NamePolicyError) Detail() string {
return e.detail
}
// NamePolicyEngine can be used to check that a CSR or Certificate meets all allowed and
// denied names before a CA creates and/or signs the Certificate.
// TODO(hs): the X509 RFC also defines name checks on directory name; support that?
// TODO(hs): implement Stringer interface: describe the contents of the NamePolicyEngine?
// TODO(hs): implement matching URI schemes, paths, etc; not just the domain part of URI domains
type NamePolicyEngine struct {
// verifySubjectCommonName is set when Subject Common Name must be verified
verifySubjectCommonName bool
// allowLiteralWildcardNames allows literal wildcard DNS domains
allowLiteralWildcardNames bool
// permitted and exluded constraints similar to x509 Name Constraints
permittedCommonNames []string
excludedCommonNames []string
permittedDNSDomains []string
excludedDNSDomains []string
permittedIPRanges []*net.IPNet
excludedIPRanges []*net.IPNet
permittedEmailAddresses []string
excludedEmailAddresses []string
permittedURIDomains []string
excludedURIDomains []string
permittedPrincipals []string
excludedPrincipals []string
// some internal counts for housekeeping
numberOfCommonNameConstraints int
numberOfDNSDomainConstraints int
numberOfIPRangeConstraints int
numberOfEmailAddressConstraints int
numberOfURIDomainConstraints int
numberOfPrincipalConstraints int
totalNumberOfPermittedConstraints int
totalNumberOfExcludedConstraints int
totalNumberOfConstraints int
}
// NewNamePolicyEngine creates a new NamePolicyEngine with NamePolicyOptions
func New(opts ...NamePolicyOption) (*NamePolicyEngine, error) {
e := &NamePolicyEngine{}
for _, option := range opts {
if err := option(e); err != nil {
return nil, err
}
}
e.permittedCommonNames = removeDuplicates(e.permittedCommonNames)
e.permittedDNSDomains = removeDuplicates(e.permittedDNSDomains)
e.permittedIPRanges = removeDuplicateIPNets(e.permittedIPRanges)
e.permittedEmailAddresses = removeDuplicates(e.permittedEmailAddresses)
e.permittedURIDomains = removeDuplicates(e.permittedURIDomains)
e.permittedPrincipals = removeDuplicates(e.permittedPrincipals)
e.excludedCommonNames = removeDuplicates(e.excludedCommonNames)
e.excludedDNSDomains = removeDuplicates(e.excludedDNSDomains)
e.excludedIPRanges = removeDuplicateIPNets(e.excludedIPRanges)
e.excludedEmailAddresses = removeDuplicates(e.excludedEmailAddresses)
e.excludedURIDomains = removeDuplicates(e.excludedURIDomains)
e.excludedPrincipals = removeDuplicates(e.excludedPrincipals)
e.numberOfCommonNameConstraints = len(e.permittedCommonNames) + len(e.excludedCommonNames)
e.numberOfDNSDomainConstraints = len(e.permittedDNSDomains) + len(e.excludedDNSDomains)
e.numberOfIPRangeConstraints = len(e.permittedIPRanges) + len(e.excludedIPRanges)
e.numberOfEmailAddressConstraints = len(e.permittedEmailAddresses) + len(e.excludedEmailAddresses)
e.numberOfURIDomainConstraints = len(e.permittedURIDomains) + len(e.excludedURIDomains)
e.numberOfPrincipalConstraints = len(e.permittedPrincipals) + len(e.excludedPrincipals)
e.totalNumberOfPermittedConstraints = len(e.permittedCommonNames) + len(e.permittedDNSDomains) +
len(e.permittedIPRanges) + len(e.permittedEmailAddresses) + len(e.permittedURIDomains) +
len(e.permittedPrincipals)
e.totalNumberOfExcludedConstraints = len(e.excludedCommonNames) + len(e.excludedDNSDomains) +
len(e.excludedIPRanges) + len(e.excludedEmailAddresses) + len(e.excludedURIDomains) +
len(e.excludedPrincipals)
e.totalNumberOfConstraints = e.totalNumberOfPermittedConstraints + e.totalNumberOfExcludedConstraints
return e, nil
}
// removeDuplicates returns a new slice of strings with
// duplicate values removed. It retains the order of elements
// in the source slice.
func removeDuplicates(items []string) (ret []string) {
// no need to remove dupes; return original
if len(items) <= 1 {
return items
}
keys := make(map[string]struct{}, len(items))
ret = make([]string, 0, len(items))
for _, item := range items {
if _, ok := keys[item]; ok {
continue
}
keys[item] = struct{}{}
ret = append(ret, item)
}
return
}
// removeDuplicateIPNets returns a new slice of net.IPNets with
// duplicate values removed. It retains the order of elements in
// the source slice. An IPNet is considered duplicate if its CIDR
// notation exists multiple times in the slice.
func removeDuplicateIPNets(items []*net.IPNet) (ret []*net.IPNet) {
// no need to remove dupes; return original
if len(items) <= 1 {
return items
}
keys := make(map[string]struct{}, len(items))
ret = make([]*net.IPNet, 0, len(items))
for _, item := range items {
key := item.String() // use CIDR notation as key
if _, ok := keys[key]; ok {
continue
}
keys[key] = struct{}{}
ret = append(ret, item)
}
// TODO(hs): implement filter of fully overlapping ranges,
// so that the smaller ones are automatically removed?
return
}
// IsX509CertificateAllowed verifies that all SANs in a Certificate are allowed.
func (e *NamePolicyEngine) IsX509CertificateAllowed(cert *x509.Certificate) error {
if err := e.validateNames(cert.DNSNames, cert.IPAddresses, cert.EmailAddresses, cert.URIs, []string{}); err != nil {
return err
}
if e.verifySubjectCommonName {
return e.validateCommonName(cert.Subject.CommonName)
}
return nil
}
// IsX509CertificateRequestAllowed verifies that all names in the CSR are allowed.
func (e *NamePolicyEngine) IsX509CertificateRequestAllowed(csr *x509.CertificateRequest) error {
if err := e.validateNames(csr.DNSNames, csr.IPAddresses, csr.EmailAddresses, csr.URIs, []string{}); err != nil {
return err
}
if e.verifySubjectCommonName {
return e.validateCommonName(csr.Subject.CommonName)
}
return nil
}
// AreSANSAllowed verifies that all names in the slice of SANs are allowed.
// The SANs are first split into DNS names, IPs, email addresses and URIs.
func (e *NamePolicyEngine) AreSANsAllowed(sans []string) error {
dnsNames, ips, emails, uris := x509util.SplitSANs(sans)
if err := e.validateNames(dnsNames, ips, emails, uris, []string{}); err != nil {
return err
}
return nil
}
// IsDNSAllowed verifies a single DNS domain is allowed.
func (e *NamePolicyEngine) IsDNSAllowed(dns string) error {
if err := e.validateNames([]string{dns}, []net.IP{}, []string{}, []*url.URL{}, []string{}); err != nil {
return err
}
return nil
}
// IsIPAllowed verifies a single IP domain is allowed.
func (e *NamePolicyEngine) IsIPAllowed(ip net.IP) error {
if err := e.validateNames([]string{}, []net.IP{ip}, []string{}, []*url.URL{}, []string{}); err != nil {
return err
}
return nil
}
// IsSSHCertificateAllowed verifies that all principals in an SSH certificate are allowed.
func (e *NamePolicyEngine) IsSSHCertificateAllowed(cert *ssh.Certificate) error {
dnsNames, ips, emails, principals, err := splitSSHPrincipals(cert)
if err != nil {
return err
}
if err := e.validateNames(dnsNames, ips, emails, []*url.URL{}, principals); err != nil {
return err
}
return nil
}
// splitPrincipals splits SSH certificate principals into DNS names, emails and usernames.
func splitSSHPrincipals(cert *ssh.Certificate) (dnsNames []string, ips []net.IP, emails, principals []string, err error) {
dnsNames = []string{}
ips = []net.IP{}
emails = []string{}
principals = []string{}
var uris []*url.URL
switch cert.CertType {
case ssh.HostCert:
dnsNames, ips, emails, uris = x509util.SplitSANs(cert.ValidPrincipals)
if len(uris) > 0 {
err = fmt.Errorf("URL principals %v not expected in SSH host certificate ", uris)
}
case ssh.UserCert:
// re-using SplitSANs results in anything that can't be parsed as an IP, URI or email
// to be considered a username principal. This allows usernames like h.slatman to be present
// in the SSH certificate. We're exluding URIs, because they can be confusing
// when used in a SSH user certificate.
principals, ips, emails, uris = x509util.SplitSANs(cert.ValidPrincipals)
if len(ips) > 0 {
err = fmt.Errorf("IP principals %v not expected in SSH user certificate ", ips)
}
if len(uris) > 0 {
err = fmt.Errorf("URL principals %v not expected in SSH user certificate ", uris)
}
default:
err = fmt.Errorf("unexpected SSH certificate type %d", cert.CertType)
}
return
}