crypto/x509: sub-quadratic name constraint checking

Previously, we implemented ~quadratic name constraint checking, wherein
we would check every SAN against every respective constraint in the
chain. This is the technique _basically everyone_ implements, because
it's easy, but it requires also capping the total number of constraint
checking operations to prevent denial of service.

Instead, this change implements a log-linear checking technique, as
originally described by davidben@google.com with some minor
modifications. The comment at the top of crypto/x509/constraints.go
describes this technique in detail.

This technique is faster than the existing quadratic approach in all but
one specific case, where there are a large number of constraints but
only a single name, since our previous algorithm resolves to linear in
that case.

Change-Id: Icb761f5f9898c04e266c0d0c2b07ab2637f03418
Reviewed-on: https://go-review.googlesource.com/c/go/+/711421
Reviewed-by: Nicholas Husin <nsh@golang.org>
Reviewed-by: Daniel McCarney <daniel@binaryparadox.net>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Roland Shoemaker <roland@golang.org>
Reviewed-by: Nicholas Husin <husin@google.com>

src/crypto/x509/constraints.go

@@ -0,0 +1,624 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package x509
+
+import (
+	"bytes"
+	"fmt"
+	"net"
+	"net/netip"
+	"net/url"
+	"slices"
+	"strings"
+)
+
+// This file contains the data structures and functions necessary for
+// efficiently checking X.509 name constraints. The method for constraint
+// checking implemented in this file is based on a technique originally
+// described by davidben@google.com.
+//
+// The basic concept is based on the fact that constraints describe possibly
+// overlapping subtrees that we need to match against. If sorted in lexicographic
+// order, and then pruned, removing any subtrees that overlap with preceding
+// subtrees, a simple binary search can be used to find the nearest matching
+// prefix. This reduces the complexity of name constraint checking from
+// quadratic to log linear complexity.
+//
+// A close reading of RFC 5280 may suggest that constraints could also be
+// implemented as a trie (or radix tree), which would present the possibility of
+// doing construction and matching in linear time, but the memory cost of
+// implementing them is actually quite high, and in the worst case (where each
+// node has a high number of children) can be abused to require a program to use
+// significant amounts of memory. The log linear approach taken here is
+// extremely cheap in terms of memory because we directly alias the already
+// parsed constraints, thus avoiding the need to do significant additional
+// allocations.
+//
+// The basic data structure is nameConstraintsSet, which implements the sorting,
+// pruning, and querying of the prefix sets.
+//
+// In order to check IP, DNS, URI, and email constraints, we need to use two
+// different techniques, one for IP addresses, which is quite simple, and one
+// for DNS names, which additionally compose the portions of URIs and emails we
+// care about (technically we also need some special logic for email addresses
+// as well for when constraints comprise of full email addresses) which is
+// slightly more complex.
+//
+// IP addresses use two nameConstraintsSets, one for IPv4 addresses and one for
+// IPv6 addresses, with no additional logic.
+//
+// DNS names require some extra logic in order to handle the distinctions
+// between permitted and excluded subtrees, as well as for wildcards, and the
+// semantics of leading period constraints (i.e. '.example.com'). This logic is
+// implemented in the dnsConstraints type.
+//
+// Email addresses also require some additional logic, which does not make use
+// of nameConstraintsSet, to handle constraints which define full email
+// addresses (i.e. 'test@example.com'). For bare domain constraints, we use the
+// dnsConstraints type described above, querying the domain portion of the email
+// address. For full email addresses, we also hold a map of email addresses that
+// map the local portion of the email to the domain. When querying full email
+// addresses we then check if the local portion of the email is present in the
+// map, and if so case insensitively compare the domain portion of the
+// email.
+
+type nameConstraintsSet[T *net.IPNet | string, V net.IP | string] struct {
+	set []T
+}
+
+// sortAndPrune sorts the constraints using the provided comparison function, and then
+// prunes any constraints that are subsets of preceding constraints using the
+// provided subset function.
+func (nc *nameConstraintsSet[T, V]) sortAndPrune(cmp func(T, T) int, subset func(T, T) bool) {
+	if len(nc.set) < 2 {
+		return
+	}
+
+	slices.SortFunc(nc.set, cmp)
+
+	if len(nc.set) < 2 {
+		return
+	}
+	writeIndex := 1
+	for readIndex := 1; readIndex < len(nc.set); readIndex++ {
+		if !subset(nc.set[writeIndex-1], nc.set[readIndex]) {
+			nc.set[writeIndex] = nc.set[readIndex]
+			writeIndex++
+		}
+	}
+	nc.set = nc.set[:writeIndex]
+}
+
+// search does a binary search over the constraints set for the provided value
+// s, using the provided comparison function cmp to find the lower bound, and
+// the match function to determine if the found constraint is a prefix of s. If
+// a matching constraint is found, it is returned along with true. If no
+// matching constraint is found, the zero value of T and false are returned.
+func (nc *nameConstraintsSet[T, V]) search(s V, cmp func(T, V) int, match func(T, V) bool) (lowerBound T, exactMatch bool) {
+	if len(nc.set) == 0 {
+		return lowerBound, false
+	}
+	// Look for the lower bound of s in the set.
+	i, found := slices.BinarySearchFunc(nc.set, s, cmp)
+	// If we found an exact match, return it
+	if found {
+		return nc.set[i], true
+	}
+
+	if i < 0 {
+		return lowerBound, false
+	}
+
+	var constraint T
+	if i == 0 {
+		constraint = nc.set[0]
+	} else {
+		constraint = nc.set[i-1]
+	}
+	if match(constraint, s) {
+		return constraint, true
+	}
+	return lowerBound, false
+}
+
+func ipNetworkSubset(a, b *net.IPNet) bool {
+	if !a.Contains(b.IP) {
+		return false
+	}
+	broadcast := make(net.IP, len(b.IP))
+	for i := range b.IP {
+		broadcast[i] = b.IP[i] | (^b.Mask[i])
+	}
+	return a.Contains(broadcast)
+}
+
+func ipNetworkCompare(a, b *net.IPNet) int {
+	i := bytes.Compare(a.IP, b.IP)
+	if i != 0 {
+		return i
+	}
+	return bytes.Compare(a.Mask, b.Mask)
+}
+
+func ipBinarySearch(constraint *net.IPNet, target net.IP) int {
+	return bytes.Compare(constraint.IP, target)
+}
+
+func ipMatch(constraint *net.IPNet, target net.IP) bool {
+	return constraint.Contains(target)
+}
+
+type ipConstraints struct {
+	// NOTE: we could store IP network prefixes as a pre-processed byte slice
+	// (i.e. by masking the IP) and doing the byte prefix checking using faster
+	// techniques, but this would require allocating new byte slices, which is
+	// likely significantly more expensive than just operating on the
+	// pre-allocated *net.IPNet and net.IP objects directly.
+
+	ipv4 *nameConstraintsSet[*net.IPNet, net.IP]
+	ipv6 *nameConstraintsSet[*net.IPNet, net.IP]
+}
+
+func newIPNetConstraints(l []*net.IPNet) interface {
+	query(net.IP) (*net.IPNet, bool)
+} {
+	if len(l) == 0 {
+		return nil
+	}
+	var ipv4, ipv6 []*net.IPNet
+	for _, n := range l {
+		if len(n.IP) == net.IPv4len {
+			ipv4 = append(ipv4, n)
+		} else {
+			ipv6 = append(ipv6, n)
+		}
+	}
+	var v4c, v6c *nameConstraintsSet[*net.IPNet, net.IP]
+	if len(ipv4) > 0 {
+		v4c = &nameConstraintsSet[*net.IPNet, net.IP]{
+			set: ipv4,
+		}
+		v4c.sortAndPrune(ipNetworkCompare, ipNetworkSubset)
+	}
+	if len(ipv6) > 0 {
+		v6c = &nameConstraintsSet[*net.IPNet, net.IP]{
+			set: ipv6,
+		}
+		v6c.sortAndPrune(ipNetworkCompare, ipNetworkSubset)
+	}
+	return &ipConstraints{ipv4: v4c, ipv6: v6c}
+}
+
+func (ipc *ipConstraints) query(ip net.IP) (*net.IPNet, bool) {
+	var c *nameConstraintsSet[*net.IPNet, net.IP]
+	if len(ip) == net.IPv4len {
+		c = ipc.ipv4
+	} else {
+		c = ipc.ipv6
+	}
+	if c == nil {
+		return nil, false
+	}
+	return c.search(ip, ipBinarySearch, ipMatch)
+}
+
+// dnsHasSuffix case-insensitively checks if DNS name b is a label suffix of DNS
+// name a, meaning that example.com is not considered a suffix of
+// testexample.com, but is a suffix of test.example.com.
+//
+// dnsHasSuffix supports the URI "leading period" constraint semantics, which
+// while not explicitly defined for dNSNames in RFC 5280, are widely supported
+// (see errata 5997). In particular, a constraint of ".example.com" is
+// considered to only match subdomains of example.com, but not example.com
+// itself.
+//
+// a and b must both be non-empty strings representing (mostly) valid DNS names.
+func dnsHasSuffix(a, b string) bool {
+	lenA := len(a)
+	lenB := len(b)
+	if lenA > lenB {
+		return false
+	}
+	i := lenA - 1
+	offset := lenA - lenB
+	for ; i >= 0; i-- {
+		ar, br := a[i], b[i-(offset)]
+		if ar == br {
+			continue
+		}
+		if br < ar {
+			ar, br = br, ar
+		}
+		if 'A' <= ar && ar <= 'Z' && br == ar+'a'-'A' {
+			continue
+		}
+		return false
+	}
+
+	if a[0] != '.' && lenB > lenA && b[lenB-lenA-1] != '.' {
+		return false
+	}
+
+	return true
+}
+
+// dnsCompareTable contains the ASCII alphabet mapped from a characters index in
+// the table to its lowercased form.
+var dnsCompareTable [256]byte
+
+func init() {
+	// NOTE: we don't actually need the
+	// full alphabet, but calculating offsets would be more expensive than just
+	// having redundant characters.
+	for i := 0; i < 256; i++ {
+		c := byte(i)
+		if 'A' <= c && c <= 'Z' {
+			// Lowercase uppercase characters A-Z.
+			c += 'a' - 'A'
+		}
+		dnsCompareTable[i] = c
+	}
+	// Set the period character to 0 so that we get the right sorting behavior.
+	//
+	// In particular, we need the period character to sort before the only
+	// other valid DNS name character which isn't a-z or 0-9, the hyphen,
+	// otherwise a name with a dash would be incorrectly sorted into the middle
+	// of another tree.
+	//
+	// For example, imagine a certificate with the constraints "a.com", "a.a.com", and
+	// "a-a.com". These would sort as "a.com", "a-a.com", "a.a.com", which would break
+	// the pruning step since we wouldn't see that "a.a.com" is a subset of "a.com".
+	// Sorting the period before the hyphen ensures that "a.a.com" sorts before "a-a.com".
+	dnsCompareTable['.'] = 0
+}
+
+// dnsCompare is a case-insensitive reversed implementation of strings.Compare
+// that operates from the end to the start of the strings. This is more
+// efficient that allocating reversed version of a and b and using
+// strings.Compare directly (even though it is highly optimized).
+//
+// NOTE: this function treats the period character ('.') as sorting above every
+// other character, which is necessary for us to properly sort names into their
+// correct order. This is further discussed in the init function above.
+func dnsCompare(a, b string) int {
+	idxA := len(a) - 1
+	idxB := len(b) - 1
+
+	for idxA >= 0 && idxB >= 0 {
+		byteA := dnsCompareTable[a[idxA]]
+		byteB := dnsCompareTable[b[idxB]]
+		if byteA == byteB {
+			idxA--
+			idxB--
+			continue
+		}
+		ret := 1
+		if byteA < byteB {
+			ret = -1
+		}
+		return ret
+	}
+
+	ret := 0
+	if idxA < idxB {
+		ret = -1
+	} else if idxB < idxA {
+		ret = 1
+	}
+	return ret
+}
+
+type dnsConstraints struct {
+	// all lets us short circuit the query logic if we see a zero length
+	// constraint which permits or excludes everything.
+	all bool
+
+	// permitted indicates if these constraints are for permitted or excluded
+	// names.
+	permitted bool
+
+	constraints *nameConstraintsSet[string, string]
+
+	// parentConstraints contains a subset of constraints which are used for
+	// wildcard SAN queries, which are constructed by removing the first label
+	// from the constraints in constraints. parentConstraints is only populated
+	// if permitted is false.
+	parentConstraints map[string]string
+}
+
+func newDNSConstraints(l []string, permitted bool) interface{ query(string) (string, bool) } {
+	if len(l) == 0 {
+		return nil
+	}
+	for _, n := range l {
+		if len(n) == 0 {
+			return &dnsConstraints{all: true}
+		}
+	}
+	constraints := slices.Clone(l)
+
+	nc := &dnsConstraints{
+		constraints: &nameConstraintsSet[string, string]{
+			set: constraints,
+		},
+		permitted: permitted,
+	}
+
+	nc.constraints.sortAndPrune(dnsCompare, dnsHasSuffix)
+
+	if !permitted {
+		parentConstraints := map[string]string{}
+		for _, name := range nc.constraints.set {
+			trimmedName := trimFirstLabel(name)
+			if trimmedName == "" {
+				continue
+			}
+			parentConstraints[trimmedName] = name
+		}
+		if len(parentConstraints) > 0 {
+			nc.parentConstraints = parentConstraints
+		}
+	}
+
+	return nc
+}
+
+func (dnc *dnsConstraints) query(s string) (string, bool) {
+	if dnc.all {
+		return "", true
+	}
+
+	constraint, match := dnc.constraints.search(s, dnsCompare, dnsHasSuffix)
+	if match {
+		return constraint, true
+	}
+
+	if !dnc.permitted && s[0] == '*' {
+		trimmed := trimFirstLabel(s)
+		if constraint, found := dnc.parentConstraints[trimmed]; found {
+			return constraint, true
+		}
+	}
+	return "", false
+}
+
+type emailConstraints struct {
+	dnsConstraints interface{ query(string) (string, bool) }
+
+	fullEmails map[string]string
+}
+
+func newEmailConstraints(l []string, permitted bool) interface {
+	query(parsedEmail) (string, bool)
+} {
+	if len(l) == 0 {
+		return nil
+	}
+	exactMap := map[string]string{}
+	var domains []string
+	for _, c := range l {
+		if !strings.ContainsRune(c, '@') {
+			domains = append(domains, c)
+			continue
+		}
+		parsed, ok := parseRFC2821Mailbox(c)
+		if !ok {
+			// We've already parsed these addresses in parseCertificate, and
+			// treat failures as a hard failure for parsing. The only way we can
+			// get a parse failure here is if the caller has mutated the
+			// certificate since parsing.
+			continue
+		}
+		exactMap[parsed.local] = parsed.domain
+	}
+	ec := &emailConstraints{
+		fullEmails: exactMap,
+	}
+	if len(domains) > 0 {
+		ec.dnsConstraints = newDNSConstraints(domains, permitted)
+	}
+	return ec
+}
+
+func (ec *emailConstraints) query(s parsedEmail) (string, bool) {
+	if len(ec.fullEmails) > 0 && strings.ContainsRune(s.email, '@') {
+		if domain, ok := ec.fullEmails[s.mailbox.local]; ok && strings.EqualFold(domain, s.mailbox.domain) {
+			return ec.fullEmails[s.email] + "@" + s.mailbox.domain, true
+		}
+	}
+	if ec.dnsConstraints == nil {
+		return "", false
+	}
+	constraint, found := ec.dnsConstraints.query(s.mailbox.domain)
+	return constraint, found
+}
+
+type constraints[T any, V any] struct {
+	constraintType string
+	permitted      interface{ query(V) (T, bool) }
+	excluded       interface{ query(V) (T, bool) }
+}
+
+func checkConstraints[T string | *net.IPNet, V any, P string | net.IP | parsedURI | parsedEmail](c constraints[T, V], s V, p P) error {
+	if c.permitted != nil {
+		if _, found := c.permitted.query(s); !found {
+			return fmt.Errorf("%s %q is not permitted by any constraint", c.constraintType, p)
+		}
+	}
+	if c.excluded != nil {
+		if constraint, found := c.excluded.query(s); found {
+			return fmt.Errorf("%s %q is excluded by constraint %q", c.constraintType, p, constraint)
+		}
+	}
+	return nil
+}
+
+type chainConstraints struct {
+	ip    constraints[*net.IPNet, net.IP]
+	dns   constraints[string, string]
+	uri   constraints[string, string]
+	email constraints[string, parsedEmail]
+
+	index int
+	next  *chainConstraints
+}
+
+func (cc *chainConstraints) check(dns []string, uris []parsedURI, emails []parsedEmail, ips []net.IP) error {
+	for _, ip := range ips {
+		if err := checkConstraints(cc.ip, ip, ip); err != nil {
+			return err
+		}
+	}
+	for _, d := range dns {
+		if !domainNameValid(d, false) {
+			return fmt.Errorf("x509: cannot parse dnsName %q", d)
+		}
+		if err := checkConstraints(cc.dns, d, d); err != nil {
+			return err
+		}
+	}
+	for _, u := range uris {
+		if !domainNameValid(u.domain, false) {
+			return fmt.Errorf("x509: internal error: URI SAN %q failed to parse", u)
+		}
+		if err := checkConstraints(cc.uri, u.domain, u); err != nil {
+			return err
+		}
+	}
+	for _, e := range emails {
+		if !domainNameValid(e.mailbox.domain, false) {
+			return fmt.Errorf("x509: cannot parse rfc822Name %q", e.mailbox)
+		}
+		if err := checkConstraints(cc.email, e, e); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func checkChainConstraints(chain []*Certificate) error {
+	var currentConstraints *chainConstraints
+	var last *chainConstraints
+	for i, c := range chain {
+		if !c.hasNameConstraints() {
+			continue
+		}
+		cc := &chainConstraints{
+			ip:    constraints[*net.IPNet, net.IP]{"IP address", newIPNetConstraints(c.PermittedIPRanges), newIPNetConstraints(c.ExcludedIPRanges)},
+			dns:   constraints[string, string]{"DNS name", newDNSConstraints(c.PermittedDNSDomains, true), newDNSConstraints(c.ExcludedDNSDomains, false)},
+			uri:   constraints[string, string]{"URI", newDNSConstraints(c.PermittedURIDomains, true), newDNSConstraints(c.ExcludedURIDomains, false)},
+			email: constraints[string, parsedEmail]{"email address", newEmailConstraints(c.PermittedEmailAddresses, true), newEmailConstraints(c.ExcludedEmailAddresses, false)},
+			index: i,
+		}
+		if currentConstraints == nil {
+			currentConstraints = cc
+			last = cc
+		} else if last != nil {
+			last.next = cc
+			last = cc
+		}
+	}
+	if currentConstraints == nil {
+		return nil
+	}
+
+	for i, c := range chain {
+		if !c.hasSANExtension() {
+			continue
+		}
+		if i >= currentConstraints.index {
+			for currentConstraints.index <= i {
+				if currentConstraints.next == nil {
+					return nil
+				}
+				currentConstraints = currentConstraints.next
+			}
+		}
+
+		uris, err := parseURIs(c.URIs)
+		if err != nil {
+			return err
+		}
+		emails, err := parseMailboxes(c.EmailAddresses)
+		if err != nil {
+			return err
+		}
+
+		for n := currentConstraints; n != nil; n = n.next {
+			if err := n.check(c.DNSNames, uris, emails, c.IPAddresses); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
+type parsedURI struct {
+	uri    *url.URL
+	domain string
+}
+
+func (u parsedURI) String() string {
+	return u.uri.String()
+}
+
+func parseURIs(uris []*url.URL) ([]parsedURI, error) {
+	parsed := make([]parsedURI, 0, len(uris))
+	for _, uri := range uris {
+		host := strings.ToLower(uri.Host)
+		if len(host) == 0 {
+			return nil, 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 nil, fmt.Errorf("cannot parse URI host %q: %v", uri.Host, err)
+			}
+		}
+
+		// netip.ParseAddr will reject the URI IPv6 literal form "[...]", so we
+		// check if _either_ the string parses as an IP, or if it is enclosed in
+		// square brackets.
+		if _, err := netip.ParseAddr(host); err == nil || (strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]")) {
+			return nil, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
+		}
+
+		parsed = append(parsed, parsedURI{uri, host})
+	}
+	return parsed, nil
+}
+
+type parsedEmail struct {
+	email   string
+	mailbox *rfc2821Mailbox
+}
+
+func (e parsedEmail) String() string {
+	return e.mailbox.local + "@" + e.mailbox.domain
+}
+
+func parseMailboxes(emails []string) ([]parsedEmail, error) {
+	parsed := make([]parsedEmail, 0, len(emails))
+	for _, email := range emails {
+		mailbox, ok := parseRFC2821Mailbox(email)
+		if !ok {
+			return nil, fmt.Errorf("cannot parse rfc822Name %q", email)
+		}
+		mailbox.domain = strings.ToLower(mailbox.domain)
+		parsed = append(parsed, parsedEmail{strings.ToLower(email), &mailbox})
+	}
+	return parsed, nil
+}
+
+func trimFirstLabel(dnsName string) string {
+	firstDotInd := strings.IndexByte(dnsName, '.')
+	if firstDotInd < 0 {
+		// Constraint is a single label, we cannot trim it.
+		return ""
+	}
+	return dnsName[firstDotInd:]
+}

src/crypto/x509/verify.go

@@ -13,9 +13,6 @@ import (
 	"iter"
 	"maps"
 	"net"
-	"net/netip"
-	"net/url"
-	"reflect"
 	"runtime"
 	"slices"
 	"strings"
@@ -430,180 +427,6 @@ func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {
 	return reverseLabels, true
 }
 
-func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string, reversedDomainsCache map[string][]string, reversedConstraintsCache map[string][]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, reversedDomainsCache, reversedConstraintsCache)
-}
-
-func matchURIConstraint(uri *url.URL, constraint string, reversedDomainsCache map[string][]string, reversedConstraintsCache map[string][]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
-		}
-	}
-
-	// netip.ParseAddr will reject the URI IPv6 literal form "[...]", so we
-	// check if _either_ the string parses as an IP, or if it is enclosed in
-	// square brackets.
-	if _, err := netip.ParseAddr(host); err == nil || (strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]")) {
-		return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
-	}
-
-	return matchDomainConstraint(host, constraint, reversedDomainsCache, reversedConstraintsCache)
-}
-
-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 matchDomainConstraint(domain, constraint string, reversedDomainsCache map[string][]string, reversedConstraintsCache map[string][]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, found := reversedDomainsCache[domain]
-	if !found {
-		var ok bool
-		domainLabels, ok = domainToReverseLabels(domain)
-		if !ok {
-			return false, fmt.Errorf("x509: internal error: cannot parse domain %q", domain)
-		}
-		reversedDomainsCache[domain] = domainLabels
-	}
-
-	// 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, found := reversedConstraintsCache[constraint]
-	if !found {
-		var ok bool
-		constraintLabels, ok = domainToReverseLabels(constraint)
-		if !ok {
-			return false, fmt.Errorf("x509: internal error: cannot parse domain %q", constraint)
-		}
-		reversedConstraintsCache[constraint] = constraintLabels
-	}
-
-	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
-}
-
-// checkNameConstraints checks that c permits a child certificate to claim the
-// given name, of type nameType. The argument parsedName contains the parsed
-// form of name, suitable for passing to the match function. The total number
-// of comparisons is tracked in the given count and should not exceed the given
-// limit.
-func (c *Certificate) checkNameConstraints(count *int,
-	maxConstraintComparisons int,
-	nameType string,
-	name string,
-	parsedName any,
-	match func(parsedName, constraint any) (match bool, err error),
-	permitted, excluded any) error {
-
-	excludedValue := reflect.ValueOf(excluded)
-
-	*count += excludedValue.Len()
-	if *count > maxConstraintComparisons {
-		return CertificateInvalidError{c, TooManyConstraints, ""}
-	}
-
-	for i := 0; i < excludedValue.Len(); i++ {
-		constraint := excludedValue.Index(i).Interface()
-		match, err := match(parsedName, constraint)
-		if err != nil {
-			return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
-		}
-
-		if match {
-			return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is excluded by constraint %q", nameType, name, constraint)}
-		}
-	}
-
-	permittedValue := reflect.ValueOf(permitted)
-
-	*count += permittedValue.Len()
-	if *count > maxConstraintComparisons {
-		return CertificateInvalidError{c, TooManyConstraints, ""}
-	}
-
-	ok := true
-	for i := 0; i < permittedValue.Len(); i++ {
-		constraint := permittedValue.Index(i).Interface()
-
-		var err error
-		if ok, err = match(parsedName, constraint); err != nil {
-			return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
-		}
-
-		if ok {
-			break
-		}
-	}
-
-	if !ok {
-		return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is not permitted by any constraint", nameType, name)}
-	}
-
-	return nil
-}
-
 // isValid performs validity checks on c given that it is a candidate to append
 // to the chain in currentChain.
 func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
@@ -636,8 +459,10 @@ func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *V
 		}
 	}
 
-	if (certType == intermediateCertificate || certType == rootCertificate) && len(currentChain) == 0 {
-		return errors.New("x509: internal error: empty chain when appending CA cert")
+	if certType == intermediateCertificate || certType == rootCertificate {
+		if len(currentChain) == 0 {
+			return errors.New("x509: internal error: empty chain when appending CA cert")
+		}
 	}
 
 	// KeyUsage status flags are ignored. From Engineering Security, Peter
@@ -794,9 +619,9 @@ func (c *Certificate) Verify(opts VerifyOptions) ([][]*Certificate, error) {
 			incompatibleKeyUsageChains++
 			return true
 		}
-		if err := checkChainConstraints(chain, opts); err != nil {
+		if err := checkChainConstraints(chain); err != nil {
 			if constraintsHintErr == nil {
-				constraintsHintErr = err
+				constraintsHintErr = CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
 			}
 			return true
 		}
@@ -1182,106 +1007,6 @@ NextCert:
 	return true
 }
 
-func checkChainConstraints(chain []*Certificate, opts VerifyOptions) error {
-	maxConstraintComparisons := opts.MaxConstraintComparisions
-	if maxConstraintComparisons == 0 {
-		maxConstraintComparisons = 250000
-	}
-	comparisonCount := 0
-
-	// Each time we do constraint checking, we need to check the constraints in
-	// the current certificate against all of the names that preceded it. We
-	// reverse these names using domainToReverseLabels, which is a relatively
-	// expensive operation. Since we check each name against each constraint,
-	// this requires us to do N*C calls to domainToReverseLabels (where N is the
-	// total number of names that preceed the certificate, and C is the total
-	// number of constraints in the certificate). By caching the results of
-	// calling domainToReverseLabels, we can reduce that to N+C calls at the
-	// cost of keeping all of the parsed names and constraints in memory until
-	// we return from isValid.
-	reversedDomainsCache := map[string][]string{}
-	reversedConstraintsCache := map[string][]string{}
-
-	for i, c := range chain {
-		if !c.hasNameConstraints() {
-			continue
-		}
-		for _, sanCert := range chain[:i] {
-			if !sanCert.hasSANExtension() {
-				continue
-			}
-			err := forEachSAN(sanCert.getSANExtension(), func(tag int, data []byte) error {
-				switch tag {
-				case nameTypeEmail:
-					name := string(data)
-					mailbox, ok := parseRFC2821Mailbox(name)
-					if !ok {
-						return fmt.Errorf("x509: cannot parse rfc822Name %q", mailbox)
-					}
-
-					if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "email address", name, mailbox,
-						func(parsedName, constraint any) (bool, error) {
-							return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string), reversedDomainsCache, reversedConstraintsCache)
-						}, c.PermittedEmailAddresses, c.ExcludedEmailAddresses); err != nil {
-						return err
-					}
-
-				case nameTypeDNS:
-					name := string(data)
-					if !domainNameValid(name, false) {
-						return fmt.Errorf("x509: cannot parse dnsName %q", name)
-					}
-
-					if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "DNS name", name, name,
-						func(parsedName, constraint any) (bool, error) {
-							return matchDomainConstraint(parsedName.(string), constraint.(string), reversedDomainsCache, reversedConstraintsCache)
-						}, c.PermittedDNSDomains, c.ExcludedDNSDomains); err != nil {
-						return err
-					}
-
-				case nameTypeURI:
-					name := string(data)
-					uri, err := url.Parse(name)
-					if err != nil {
-						return fmt.Errorf("x509: internal error: URI SAN %q failed to parse", name)
-					}
-
-					if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "URI", name, uri,
-						func(parsedName, constraint any) (bool, error) {
-							return matchURIConstraint(parsedName.(*url.URL), constraint.(string), reversedDomainsCache, reversedConstraintsCache)
-						}, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil {
-						return err
-					}
-
-				case nameTypeIP:
-					ip := net.IP(data)
-					if l := len(ip); l != net.IPv4len && l != net.IPv6len {
-						return fmt.Errorf("x509: internal error: IP SAN %x failed to parse", data)
-					}
-
-					if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip,
-						func(parsedName, constraint any) (bool, error) {
-							return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet))
-						}, c.PermittedIPRanges, c.ExcludedIPRanges); err != nil {
-						return err
-					}
-
-				default:
-					// Unknown SAN types are ignored.
-				}
-
-				return nil
-			})
-
-			if err != nil {
-				return err
-			}
-		}
-	}
-
-	return nil
-}
-
 func mustNewOIDFromInts(ints []uint64) OID {
 	oid, err := OIDFromInts(ints)
 	if err != nil {

src/crypto/x509/verify_test.go

@@ -1331,45 +1331,6 @@ func TestUnknownAuthorityError(t *testing.T) {
 	}
 }
 
-var nameConstraintTests = []struct {
-	constraint, domain string
-	expectError        bool
-	shouldMatch        bool
-}{
-	{"", "anything.com", false, true},
-	{"example.com", "example.com", false, true},
-	{"example.com.", "example.com", true, false},
-	{"example.com", "example.com.", true, false},
-	{"example.com", "ExAmPle.coM", false, true},
-	{"example.com", "exampl1.com", false, false},
-	{"example.com", "www.ExAmPle.coM", false, true},
-	{"example.com", "sub.www.ExAmPle.coM", false, true},
-	{"example.com", "notexample.com", false, false},
-	{".example.com", "example.com", false, false},
-	{".example.com", "www.example.com", false, true},
-	{".example.com", "www..example.com", true, false},
-}
-
-func TestNameConstraints(t *testing.T) {
-	for i, test := range nameConstraintTests {
-		result, err := matchDomainConstraint(test.domain, test.constraint, map[string][]string{}, map[string][]string{})
-
-		if err != nil && !test.expectError {
-			t.Errorf("unexpected error for test #%d: domain=%s, constraint=%s, err=%s", i, test.domain, test.constraint, err)
-			continue
-		}
-
-		if err == nil && test.expectError {
-			t.Errorf("unexpected success for test #%d: domain=%s, constraint=%s", i, test.domain, test.constraint)
-			continue
-		}
-
-		if result != test.shouldMatch {
-			t.Errorf("unexpected result for test #%d: domain=%s, constraint=%s, result=%t", i, test.domain, test.constraint, result)
-		}
-	}
-}
-
 const selfSignedWithCommonName = `-----BEGIN CERTIFICATE-----
 MIIDCjCCAfKgAwIBAgIBADANBgkqhkiG9w0BAQsFADAaMQswCQYDVQQKEwJjYTEL
 MAkGA1UEAxMCY2EwHhcNMTYwODI4MTcwOTE4WhcNMjEwODI3MTcwOTE4WjAcMQsw