Initial work on name constraints validation

Issue #1060

authority/internal/constraints/constraints.go

@@ -0,0 +1,106 @@
+package constraints
+
+import (
+	"crypto/x509"
+	"fmt"
+	"net"
+	"net/url"
+)
+
+var oidExtensionNameConstraints = []int{2, 5, 29, 30}
+
+type ConstraintError struct {
+	Type string
+	Name string
+}
+
+func (e ConstraintError) Error() string {
+	return fmt.Sprintf("%s %q is not allowed", e.Type, e.Name)
+}
+
+type service struct {
+	hasNameConstraints      bool
+	permittedDNSDomains     []string
+	excludedDNSDomains      []string
+	permittedIPRanges       []*net.IPNet
+	excludedIPRanges        []*net.IPNet
+	permittedEmailAddresses []string
+	excludedEmailAddresses  []string
+	permittedURIDomains     []string
+	excludedURIDomains      []string
+}
+
+func New(chain ...*x509.Certificate) *service {
+	s := new(service)
+	for _, crt := range chain {
+		s.permittedDNSDomains = append(s.permittedDNSDomains, crt.PermittedDNSDomains...)
+		s.excludedDNSDomains = append(s.excludedDNSDomains, crt.ExcludedDNSDomains...)
+		s.permittedIPRanges = append(s.permittedIPRanges, crt.PermittedIPRanges...)
+		s.excludedIPRanges = append(s.excludedIPRanges, crt.ExcludedIPRanges...)
+		s.permittedEmailAddresses = append(s.permittedEmailAddresses, crt.PermittedEmailAddresses...)
+		s.excludedEmailAddresses = append(s.excludedEmailAddresses, crt.ExcludedEmailAddresses...)
+		s.permittedURIDomains = append(s.permittedURIDomains, crt.PermittedURIDomains...)
+		s.excludedURIDomains = append(s.excludedURIDomains, crt.ExcludedURIDomains...)
+
+		if !s.hasNameConstraints {
+			for _, ext := range crt.Extensions {
+				if ext.Id.Equal(oidExtensionNameConstraints) {
+					s.hasNameConstraints = true
+					break
+				}
+			}
+		}
+	}
+	return s
+}
+
+// Validates
+func (s *service) Validate(dnsNames []string, ipAddresses []*net.IP, emailAddresses []string, uris []*url.URL) error {
+	if !s.hasNameConstraints {
+		return nil
+	}
+
+	for _, name := range dnsNames {
+		if err := checkNameConstraints("DNS name", name, name, s.permittedDNSDomains, s.excludedDNSDomains,
+			func(parsedName, constraint any) (bool, error) {
+				return matchDomainConstraint(parsedName.(string), constraint.(string))
+			},
+		); err != nil {
+			return err
+		}
+	}
+
+	for _, ip := range ipAddresses {
+		if err := checkNameConstraints("IP address", ip.String(), ip, s.permittedIPRanges, s.excludedIPRanges,
+			func(parsedName, constraint any) (bool, error) {
+				return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet))
+			}); err != nil {
+			return err
+		}
+	}
+
+	for _, email := range emailAddresses {
+		mailbox, ok := parseRFC2821Mailbox(email)
+		if !ok {
+			return fmt.Errorf("cannot parse rfc822Name %q", email)
+		}
+		if err := checkNameConstraints("Email address", email, mailbox, s.permittedEmailAddresses, s.excludedEmailAddresses,
+			func(parsedName, constraint any) (bool, error) {
+				return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string))
+			},
+		); err != nil {
+			return err
+		}
+	}
+
+	for _, uri := range uris {
+		if err := checkNameConstraints("URI", uri.String(), uri, s.permittedURIDomains, s.excludedURIDomains,
+			func(parsedName, constraint any) (bool, error) {
+				return matchURIConstraint(parsedName.(*url.URL), constraint.(string))
+			}); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}

authority/internal/constraints/constraints_test.go

@@ -0,0 +1,140 @@
+package constraints
+
+import (
+	"crypto/x509"
+	"net"
+	"net/url"
+	"reflect"
+	"testing"
+
+	"go.step.sm/crypto/minica"
+)
+
+func TestNew(t *testing.T) {
+	ca1, err := minica.New()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ca2, err := minica.New(
+		minica.WithIntermediateTemplate(`{
+			"subject": {{ toJson .Subject }},
+			"keyUsage": ["certSign", "crlSign"],
+			"basicConstraints": {
+				"isCA": true,
+				"maxPathLen": 0
+			},
+			"nameConstraints": {
+				"critical": true,
+				"permittedDNSDomains": ["internal.example.org"],
+				"excludedDNSDomains": ["internal.example.com"],
+				"permittedIPRanges": ["192.168.1.0/24", "192.168.2.1/32"],
+				"excludedIPRanges": ["192.168.3.0/24", "192.168.4.0/28"],
+				"permittedEmailAddresses": ["root@example.org", "example.org", ".acme.org"],
+				"excludedEmailAddresses": ["root@example.com", "example.com", ".acme.com"],
+				"permittedURIDomains": ["host.example.org", ".acme.org"],
+				"excludedURIDomains": ["host.example.com", ".acme.com"]
+			}
+		}`),
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	type args struct {
+		chain []*x509.Certificate
+	}
+	tests := []struct {
+		name string
+		args args
+		want *service
+	}{
+		{"ok", args{[]*x509.Certificate{ca1.Intermediate, ca1.Root}}, &service{
+			hasNameConstraints: false,
+		}},
+		{"ok with constraints", args{[]*x509.Certificate{ca2.Intermediate, ca2.Root}}, &service{
+			hasNameConstraints:  true,
+			permittedDNSDomains: []string{"internal.example.org"},
+			excludedDNSDomains:  []string{"internal.example.com"},
+			permittedIPRanges: []*net.IPNet{
+				{IP: net.ParseIP("192.168.1.0").To4(), Mask: net.IPMask{255, 255, 255, 0}},
+				{IP: net.ParseIP("192.168.2.1").To4(), Mask: net.IPMask{255, 255, 255, 255}},
+			},
+			excludedIPRanges: []*net.IPNet{
+				{IP: net.ParseIP("192.168.3.0").To4(), Mask: net.IPMask{255, 255, 255, 0}},
+				{IP: net.ParseIP("192.168.4.0").To4(), Mask: net.IPMask{255, 255, 255, 240}},
+			},
+			permittedEmailAddresses: []string{"root@example.org", "example.org", ".acme.org"},
+			excludedEmailAddresses:  []string{"root@example.com", "example.com", ".acme.com"},
+			permittedURIDomains:     []string{"host.example.org", ".acme.org"},
+			excludedURIDomains:      []string{"host.example.com", ".acme.com"},
+		}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := New(tt.args.chain...); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("New() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_service_Validate(t *testing.T) {
+
+	type fields struct {
+		hasNameConstraints      bool
+		permittedDNSDomains     []string
+		excludedDNSDomains      []string
+		permittedIPRanges       []*net.IPNet
+		excludedIPRanges        []*net.IPNet
+		permittedEmailAddresses []string
+		excludedEmailAddresses  []string
+		permittedURIDomains     []string
+		excludedURIDomains      []string
+	}
+	type args struct {
+		dnsNames       []string
+		ipAddresses    []*net.IP
+		emailAddresses []string
+		uris           []*url.URL
+	}
+	tests := []struct {
+		name    string
+		fields  fields
+		args    args
+		wantErr bool
+	}{
+		{"ok", fields{hasNameConstraints: false}, args{
+			dnsNames:       []string{"example.com", "host.example.com"},
+			ipAddresses:    []*net.IP{{192, 168, 1, 1}, {0x26, 0x00, 0x1f, 0x1c, 0x47, 0x1, 0x9d, 0x00, 0xc3, 0xa7, 0x66, 0x94, 0x87, 0x0f, 0x20, 0x72}},
+			emailAddresses: []string{"root@example.com"},
+			uris:           []*url.URL{{Scheme: "https", Host: "example.com", Path: "/uuid/c6d1a755-0c12-431e-9136-b64cb3173ec7"}},
+		}, false},
+		// {"ok dns", fields{}, args{}, false},
+		// {"ok ip", fields{}, args{}, false},
+		// {"ok email", fields{}, args{}, false},
+		// {"ok uri", fields{}, args{}, false},
+		// {"fail dns", fields{}, args{}, true},
+		// {"fail ip", fields{}, args{}, true},
+		// {"fail email", fields{}, args{}, true},
+		// {"fail uri", fields{}, args{}, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			s := &service{
+				hasNameConstraints:      tt.fields.hasNameConstraints,
+				permittedDNSDomains:     tt.fields.permittedDNSDomains,
+				excludedDNSDomains:      tt.fields.excludedDNSDomains,
+				permittedIPRanges:       tt.fields.permittedIPRanges,
+				excludedIPRanges:        tt.fields.excludedIPRanges,
+				permittedEmailAddresses: tt.fields.permittedEmailAddresses,
+				excludedEmailAddresses:  tt.fields.excludedEmailAddresses,
+				permittedURIDomains:     tt.fields.permittedURIDomains,
+				excludedURIDomains:      tt.fields.excludedURIDomains,
+			}
+			if err := s.Validate(tt.args.dnsNames, tt.args.ipAddresses, tt.args.emailAddresses, tt.args.uris); (err != nil) != tt.wantErr {
+				t.Errorf("service.Validate() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}

authority/internal/constraints/verify.go

@@ -0,0 +1,358 @@
+// Copyright (c) 2009 The Go Authors. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package constraints
+
+import (
+	"bytes"
+	"fmt"
+	"net"
+	"net/url"
+	"reflect"
+	"strings"
+)
+
+func checkNameConstraints(nameType string, name string, parsedName any, permitted, excluded any, match func(name, constraint any) (bool, error)) error {
+	excludedValue := reflect.ValueOf(excluded)
+	for i := 0; i < excludedValue.Len(); i++ {
+		constraint := excludedValue.Index(i).Interface()
+		match, err := match(parsedName, constraint)
+		if err != nil {
+			return err
+		}
+
+		if match {
+			return fmt.Errorf("%s %q is excluded by constraint %q", nameType, name, constraint)
+		}
+	}
+
+	var (
+		err error
+		ok  = true
+	)
+
+	permittedValue := reflect.ValueOf(permitted)
+	for i := 0; i < permittedValue.Len(); i++ {
+		constraint := permittedValue.Index(i).Interface()
+		if ok, err = match(parsedName, constraint); err != nil {
+			return err
+		}
+		if ok {
+			break
+		}
+	}
+	if !ok {
+		return fmt.Errorf("%s %q is not permitted by any constraint", nameType, name)
+	}
+
+	return nil
+}
+
+func matchDomainConstraint(domain, constraint string) (bool, error) {
+	// The meaning of zero length constraints is not specified, but this
+	// code follows NSS and accepts them as matching everything.
+	if len(constraint) == 0 {
+		return true, nil
+	}
+
+	domainLabels, ok := domainToReverseLabels(domain)
+	if !ok {
+		return false, fmt.Errorf("x509: internal error: cannot parse domain %q", domain)
+	}
+
+	// RFC 5280 says that a leading period in a domain name means that at
+	// least one label must be prepended, but only for URI and email
+	// constraints, not DNS constraints. The code also supports that
+	// behaviour for DNS constraints.
+
+	mustHaveSubdomains := false
+	if constraint[0] == '.' {
+		mustHaveSubdomains = true
+		constraint = constraint[1:]
+	}
+
+	constraintLabels, ok := domainToReverseLabels(constraint)
+	if !ok {
+		return false, fmt.Errorf("x509: internal error: cannot parse domain %q", constraint)
+	}
+
+	if len(domainLabels) < len(constraintLabels) ||
+		(mustHaveSubdomains && len(domainLabels) == len(constraintLabels)) {
+		return false, nil
+	}
+
+	for i, constraintLabel := range constraintLabels {
+		if !strings.EqualFold(constraintLabel, domainLabels[i]) {
+			return false, nil
+		}
+	}
+
+	return true, nil
+}
+
+func matchIPConstraint(ip net.IP, constraint *net.IPNet) (bool, error) {
+	if len(ip) != len(constraint.IP) {
+		return false, nil
+	}
+
+	for i := range ip {
+		if mask := constraint.Mask[i]; ip[i]&mask != constraint.IP[i]&mask {
+			return false, nil
+		}
+	}
+
+	return true, nil
+}
+
+func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string) (bool, error) {
+	// If the constraint contains an @, then it specifies an exact mailbox
+	// name.
+	if strings.Contains(constraint, "@") {
+		constraintMailbox, ok := parseRFC2821Mailbox(constraint)
+		if !ok {
+			return false, fmt.Errorf("x509: internal error: cannot parse constraint %q", constraint)
+		}
+		return mailbox.local == constraintMailbox.local && strings.EqualFold(mailbox.domain, constraintMailbox.domain), nil
+	}
+
+	// Otherwise the constraint is like a DNS constraint of the domain part
+	// of the mailbox.
+	return matchDomainConstraint(mailbox.domain, constraint)
+}
+
+func matchURIConstraint(uri *url.URL, constraint string) (bool, error) {
+	// From RFC 5280, Section 4.2.1.10:
+	// “a uniformResourceIdentifier that does not include an authority
+	// component with a host name specified as a fully qualified domain
+	// name (e.g., if the URI either does not include an authority
+	// component or includes an authority component in which the host name
+	// is specified as an IP address), then the application MUST reject the
+	// certificate.”
+
+	host := uri.Host
+	if len(host) == 0 {
+		return false, fmt.Errorf("URI with empty host (%q) cannot be matched against constraints", uri.String())
+	}
+
+	if strings.Contains(host, ":") && !strings.HasSuffix(host, "]") {
+		var err error
+		host, _, err = net.SplitHostPort(uri.Host)
+		if err != nil {
+			return false, err
+		}
+	}
+
+	if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") ||
+		net.ParseIP(host) != nil {
+		return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
+	}
+
+	return matchDomainConstraint(host, constraint)
+}
+
+// domainToReverseLabels converts a textual domain name like foo.example.com to
+// the list of labels in reverse order, e.g. ["com", "example", "foo"].
+func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {
+	for len(domain) > 0 {
+		if i := strings.LastIndexByte(domain, '.'); i == -1 {
+			reverseLabels = append(reverseLabels, domain)
+			domain = ""
+		} else {
+			reverseLabels = append(reverseLabels, domain[i+1:])
+			domain = domain[:i]
+		}
+	}
+
+	if len(reverseLabels) > 0 && len(reverseLabels[0]) == 0 {
+		// An empty label at the end indicates an absolute value.
+		return nil, false
+	}
+
+	for _, label := range reverseLabels {
+		if len(label) == 0 {
+			// Empty labels are otherwise invalid.
+			return nil, false
+		}
+
+		for _, c := range label {
+			if c < 33 || c > 126 {
+				// Invalid character.
+				return nil, false
+			}
+		}
+	}
+
+	return reverseLabels, true
+}
+
+// rfc2821Mailbox represents a “mailbox” (which is an email address to most
+// people) by breaking it into the “local” (i.e. before the '@') and “domain”
+// parts.
+type rfc2821Mailbox struct {
+	local, domain string
+}
+
+// parseRFC2821Mailbox parses an email address into local and domain parts,
+// based on the ABNF for a “Mailbox” from RFC 2821. According to RFC 5280,
+// Section 4.2.1.6 that's correct for an rfc822Name from a certificate: “The
+// format of an rfc822Name is a "Mailbox" as defined in RFC 2821, Section 4.1.2”.
+func parseRFC2821Mailbox(in string) (mailbox rfc2821Mailbox, ok bool) {
+	if len(in) == 0 {
+		return mailbox, false
+	}
+
+	localPartBytes := make([]byte, 0, len(in)/2)
+
+	if in[0] == '"' {
+		// Quoted-string = DQUOTE *qcontent DQUOTE
+		// non-whitespace-control = %d1-8 / %d11 / %d12 / %d14-31 / %d127
+		// qcontent = qtext / quoted-pair
+		// qtext = non-whitespace-control /
+		//         %d33 / %d35-91 / %d93-126
+		// quoted-pair = ("\" text) / obs-qp
+		// text = %d1-9 / %d11 / %d12 / %d14-127 / obs-text
+		//
+		// (Names beginning with “obs-” are the obsolete syntax from RFC 2822,
+		// Section 4. Since it has been 16 years, we no longer accept that.)
+		in = in[1:]
+	QuotedString:
+		for {
+			if len(in) == 0 {
+				return mailbox, false
+			}
+			c := in[0]
+			in = in[1:]
+
+			switch {
+			case c == '"':
+				break QuotedString
+
+			case c == '\\':
+				// quoted-pair
+				if len(in) == 0 {
+					return mailbox, false
+				}
+				if in[0] == 11 ||
+					in[0] == 12 ||
+					(1 <= in[0] && in[0] <= 9) ||
+					(14 <= in[0] && in[0] <= 127) {
+					localPartBytes = append(localPartBytes, in[0])
+					in = in[1:]
+				} else {
+					return mailbox, false
+				}
+
+			case c == 11 ||
+				c == 12 ||
+				// Space (char 32) is not allowed based on the
+				// BNF, but RFC 3696 gives an example that
+				// assumes that it is. Several “verified”
+				// errata continue to argue about this point.
+				// We choose to accept it.
+				c == 32 ||
+				c == 33 ||
+				c == 127 ||
+				(1 <= c && c <= 8) ||
+				(14 <= c && c <= 31) ||
+				(35 <= c && c <= 91) ||
+				(93 <= c && c <= 126):
+				// qtext
+				localPartBytes = append(localPartBytes, c)
+
+			default:
+				return mailbox, false
+			}
+		}
+	} else {
+		// Atom ("." Atom)*
+	NextChar:
+		for len(in) > 0 {
+			// atext from RFC 2822, Section 3.2.4
+			c := in[0]
+
+			switch {
+			case c == '\\':
+				// Examples given in RFC 3696 suggest that
+				// escaped characters can appear outside of a
+				// quoted string. Several “verified” errata
+				// continue to argue the point. We choose to
+				// accept it.
+				in = in[1:]
+				if len(in) == 0 {
+					return mailbox, false
+				}
+				fallthrough
+
+			case ('0' <= c && c <= '9') ||
+				('a' <= c && c <= 'z') ||
+				('A' <= c && c <= 'Z') ||
+				c == '!' || c == '#' || c == '$' || c == '%' ||
+				c == '&' || c == '\'' || c == '*' || c == '+' ||
+				c == '-' || c == '/' || c == '=' || c == '?' ||
+				c == '^' || c == '_' || c == '`' || c == '{' ||
+				c == '|' || c == '}' || c == '~' || c == '.':
+				localPartBytes = append(localPartBytes, in[0])
+				in = in[1:]
+
+			default:
+				break NextChar
+			}
+		}
+
+		if len(localPartBytes) == 0 {
+			return mailbox, false
+		}
+
+		// From RFC 3696, Section 3:
+		// “period (".") may also appear, but may not be used to start
+		// or end the local part, nor may two or more consecutive
+		// periods appear.”
+		twoDots := []byte{'.', '.'}
+		if localPartBytes[0] == '.' ||
+			localPartBytes[len(localPartBytes)-1] == '.' ||
+			bytes.Contains(localPartBytes, twoDots) {
+			return mailbox, false
+		}
+	}
+
+	if len(in) == 0 || in[0] != '@' {
+		return mailbox, false
+	}
+	in = in[1:]
+
+	// The RFC species a format for domains, but that's known to be
+	// violated in practice so we accept that anything after an '@' is the
+	// domain part.
+	if _, ok := domainToReverseLabels(in); !ok {
+		return mailbox, false
+	}
+
+	mailbox.local = string(localPartBytes)
+	mailbox.domain = in
+	return mailbox, true
+}