blob: eed0741d200f42e29f7e25ebb1688d03b5dc3d2a [file] [log] [blame]
// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "net/cert/pki/name_constraints.h"
#include <limits.h>
#include <memory>
#include "base/numerics/clamped_math.h"
#include "net/cert/pki/cert_errors.h"
#include "net/cert/pki/common_cert_errors.h"
#include "net/cert/pki/string_util.h"
#include "net/cert/pki/verify_name_match.h"
#include "net/der/input.h"
#include "net/der/parser.h"
#include "net/der/tag.h"
#include "third_party/abseil-cpp/absl/types/optional.h"
namespace net {
namespace {
// The name types of GeneralName that are fully supported in name constraints.
//
// (The other types will have the minimal checking described by RFC 5280
// section 4.2.1.10: If a name constraints extension that is marked as critical
// imposes constraints on a particular name form, and an instance of
// that name form appears in the subject field or subjectAltName
// extension of a subsequent certificate, then the application MUST
// either process the constraint or reject the certificate.)
const int kSupportedNameTypes = GENERAL_NAME_DNS_NAME |
GENERAL_NAME_DIRECTORY_NAME |
GENERAL_NAME_IP_ADDRESS;
// Controls wildcard handling of DNSNameMatches.
// If WildcardMatchType is WILDCARD_PARTIAL_MATCH "*.bar.com" is considered to
// match the constraint "foo.bar.com". If it is WILDCARD_FULL_MATCH, "*.bar.com"
// will match "bar.com" but not "foo.bar.com".
enum WildcardMatchType { WILDCARD_PARTIAL_MATCH, WILDCARD_FULL_MATCH };
// Returns true if |name| falls in the subtree defined by |dns_constraint|.
// RFC 5280 section 4.2.1.10:
// DNS name restrictions are expressed as host.example.com. Any DNS
// name that can be constructed by simply adding zero or more labels
// to the left-hand side of the name satisfies the name constraint. For
// example, www.host.example.com would satisfy the constraint but
// host1.example.com would not.
//
// |wildcard_matching| controls handling of wildcard names (|name| starts with
// "*."). Wildcard handling is not specified by RFC 5280, but certificate
// verification allows it, name constraints must check it similarly.
bool DNSNameMatches(std::string_view name,
std::string_view dns_constraint,
WildcardMatchType wildcard_matching) {
// Everything matches the empty DNS name constraint.
if (dns_constraint.empty())
return true;
// Normalize absolute DNS names by removing the trailing dot, if any.
if (!name.empty() && *name.rbegin() == '.')
name.remove_suffix(1);
if (!dns_constraint.empty() && *dns_constraint.rbegin() == '.')
dns_constraint.remove_suffix(1);
// Wildcard partial-match handling ("*.bar.com" matching name constraint
// "foo.bar.com"). This only handles the case where the the dnsname and the
// constraint match after removing the leftmost label, otherwise it is handled
// by falling through to the check of whether the dnsname is fully within or
// fully outside of the constraint.
if (wildcard_matching == WILDCARD_PARTIAL_MATCH && name.size() > 2 &&
name[0] == '*' && name[1] == '.') {
size_t dns_constraint_dot_pos = dns_constraint.find('.');
if (dns_constraint_dot_pos != std::string::npos) {
std::string_view dns_constraint_domain =
dns_constraint.substr(dns_constraint_dot_pos + 1);
std::string_view wildcard_domain = name.substr(2);
if (net::string_util::IsEqualNoCase(wildcard_domain,
dns_constraint_domain)) {
return true;
}
}
}
if (!net::string_util::EndsWithNoCase(name, dns_constraint)) {
return false;
}
// Exact match.
if (name.size() == dns_constraint.size())
return true;
// If dNSName constraint starts with a dot, only subdomains should match.
// (e.g., "foo.bar.com" matches constraint ".bar.com", but "bar.com" doesn't.)
// RFC 5280 is ambiguous, but this matches the behavior of other platforms.
if (!dns_constraint.empty() && dns_constraint[0] == '.')
dns_constraint.remove_prefix(1);
// Subtree match.
if (name.size() > dns_constraint.size() &&
name[name.size() - dns_constraint.size() - 1] == '.') {
return true;
}
// Trailing text matches, but not in a subtree (e.g., "foobar.com" is not a
// match for "bar.com").
return false;
}
// Parses a GeneralSubtrees |value| and store the contents in |subtrees|.
// The individual values stored into |subtrees| are not validated by this
// function.
// NOTE: |subtrees| is not pre-initialized by the function(it is expected to be
// a default initialized object), and it will be modified regardless of the
// return value.
[[nodiscard]] bool ParseGeneralSubtrees(const der::Input& value,
GeneralNames* subtrees,
CertErrors* errors) {
DCHECK(errors);
// GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree
//
// GeneralSubtree ::= SEQUENCE {
// base GeneralName,
// minimum [0] BaseDistance DEFAULT 0,
// maximum [1] BaseDistance OPTIONAL }
//
// BaseDistance ::= INTEGER (0..MAX)
der::Parser sequence_parser(value);
// The GeneralSubtrees sequence should have at least 1 element.
if (!sequence_parser.HasMore())
return false;
while (sequence_parser.HasMore()) {
der::Parser subtree_sequence;
if (!sequence_parser.ReadSequence(&subtree_sequence))
return false;
der::Input raw_general_name;
if (!subtree_sequence.ReadRawTLV(&raw_general_name))
return false;
if (!ParseGeneralName(raw_general_name,
GeneralNames::IP_ADDRESS_AND_NETMASK, subtrees,
errors)) {
errors->AddError(kFailedParsingGeneralName);
return false;
}
// RFC 5280 section 4.2.1.10:
// Within this profile, the minimum and maximum fields are not used with any
// name forms, thus, the minimum MUST be zero, and maximum MUST be absent.
// However, if an application encounters a critical name constraints
// extension that specifies other values for minimum or maximum for a name
// form that appears in a subsequent certificate, the application MUST
// either process these fields or reject the certificate.
// Note that technically failing here isn't required: rather only need to
// fail if a name of this type actually appears in a subsequent cert and
// this extension was marked critical. However the minimum and maximum
// fields appear uncommon enough that implementing that isn't useful.
if (subtree_sequence.HasMore())
return false;
}
return true;
}
} // namespace
NameConstraints::~NameConstraints() = default;
// static
std::unique_ptr<NameConstraints> NameConstraints::Create(
const der::Input& extension_value,
bool is_critical,
CertErrors* errors) {
DCHECK(errors);
auto name_constraints = std::make_unique<NameConstraints>();
if (!name_constraints->Parse(extension_value, is_critical, errors))
return nullptr;
return name_constraints;
}
bool NameConstraints::Parse(const der::Input& extension_value,
bool is_critical,
CertErrors* errors) {
DCHECK(errors);
der::Parser extension_parser(extension_value);
der::Parser sequence_parser;
// NameConstraints ::= SEQUENCE {
// permittedSubtrees [0] GeneralSubtrees OPTIONAL,
// excludedSubtrees [1] GeneralSubtrees OPTIONAL }
if (!extension_parser.ReadSequence(&sequence_parser))
return false;
if (extension_parser.HasMore())
return false;
absl::optional<der::Input> permitted_subtrees_value;
if (!sequence_parser.ReadOptionalTag(der::ContextSpecificConstructed(0),
&permitted_subtrees_value)) {
return false;
}
if (permitted_subtrees_value &&
!ParseGeneralSubtrees(permitted_subtrees_value.value(),
&permitted_subtrees_, errors)) {
return false;
}
constrained_name_types_ |=
permitted_subtrees_.present_name_types &
(is_critical ? GENERAL_NAME_ALL_TYPES : kSupportedNameTypes);
absl::optional<der::Input> excluded_subtrees_value;
if (!sequence_parser.ReadOptionalTag(der::ContextSpecificConstructed(1),
&excluded_subtrees_value)) {
return false;
}
if (excluded_subtrees_value &&
!ParseGeneralSubtrees(excluded_subtrees_value.value(),
&excluded_subtrees_, errors)) {
return false;
}
constrained_name_types_ |=
excluded_subtrees_.present_name_types &
(is_critical ? GENERAL_NAME_ALL_TYPES : kSupportedNameTypes);
// RFC 5280 section 4.2.1.10:
// Conforming CAs MUST NOT issue certificates where name constraints is an
// empty sequence. That is, either the permittedSubtrees field or the
// excludedSubtrees MUST be present.
if (!permitted_subtrees_value && !excluded_subtrees_value)
return false;
if (sequence_parser.HasMore())
return false;
return true;
}
void NameConstraints::IsPermittedCert(const der::Input& subject_rdn_sequence,
const GeneralNames* subject_alt_names,
CertErrors* errors) const {
// Checking NameConstraints is O(number_of_names * number_of_constraints).
// Impose a hard limit to mitigate the use of name constraints as a DoS
// mechanism.
const size_t kMaxChecks = 1048576; // 1 << 20
base::ClampedNumeric<size_t> check_count = 0;
if (subject_alt_names) {
check_count +=
base::ClampMul(subject_alt_names->dns_names.size(),
base::ClampAdd(excluded_subtrees_.dns_names.size(),
permitted_subtrees_.dns_names.size()));
check_count += base::ClampMul(
subject_alt_names->directory_names.size(),
base::ClampAdd(excluded_subtrees_.directory_names.size(),
permitted_subtrees_.directory_names.size()));
check_count += base::ClampMul(
subject_alt_names->ip_addresses.size(),
base::ClampAdd(excluded_subtrees_.ip_address_ranges.size(),
permitted_subtrees_.ip_address_ranges.size()));
}
if (!(subject_alt_names && subject_rdn_sequence.Length() == 0)) {
check_count += base::ClampAdd(excluded_subtrees_.directory_names.size(),
permitted_subtrees_.directory_names.size());
}
if (check_count > kMaxChecks) {
errors->AddError(cert_errors::kTooManyNameConstraintChecks);
return;
}
// Subject Alternative Name handling:
//
// RFC 5280 section 4.2.1.6:
// id-ce-subjectAltName OBJECT IDENTIFIER ::= { id-ce 17 }
//
// SubjectAltName ::= GeneralNames
//
// GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName
if (subject_alt_names) {
// Check unsupported name types:
// constrained_name_types() for the unsupported types will only be true if
// that type of name was present in a name constraint that was marked
// critical.
//
// RFC 5280 section 4.2.1.10:
// If a name constraints extension that is marked as critical
// imposes constraints on a particular name form, and an instance of
// that name form appears in the subject field or subjectAltName
// extension of a subsequent certificate, then the application MUST
// either process the constraint or reject the certificate.
if (constrained_name_types() & subject_alt_names->present_name_types &
~kSupportedNameTypes) {
errors->AddError(cert_errors::kNotPermittedByNameConstraints);
return;
}
// Check supported name types:
for (const auto& dns_name : subject_alt_names->dns_names) {
if (!IsPermittedDNSName(dns_name)) {
errors->AddError(cert_errors::kNotPermittedByNameConstraints);
return;
}
}
for (const auto& directory_name : subject_alt_names->directory_names) {
if (!IsPermittedDirectoryName(directory_name)) {
errors->AddError(cert_errors::kNotPermittedByNameConstraints);
return;
}
}
for (const auto& ip_address : subject_alt_names->ip_addresses) {
if (!IsPermittedIP(ip_address)) {
errors->AddError(cert_errors::kNotPermittedByNameConstraints);
return;
}
}
}
// Subject handling:
// RFC 5280 section 4.2.1.10:
// Legacy implementations exist where an electronic mail address is embedded
// in the subject distinguished name in an attribute of type emailAddress
// (Section 4.1.2.6). When constraints are imposed on the rfc822Name name
// form, but the certificate does not include a subject alternative name, the
// rfc822Name constraint MUST be applied to the attribute of type emailAddress
// in the subject distinguished name.
if (!subject_alt_names &&
(constrained_name_types() & GENERAL_NAME_RFC822_NAME)) {
bool contained_email_address = false;
if (!NameContainsEmailAddress(subject_rdn_sequence,
&contained_email_address)) {
errors->AddError(cert_errors::kNotPermittedByNameConstraints);
return;
}
if (contained_email_address) {
errors->AddError(cert_errors::kNotPermittedByNameConstraints);
return;
}
}
// RFC 5280 4.1.2.6:
// If subject naming information is present only in the subjectAltName
// extension (e.g., a key bound only to an email address or URI), then the
// subject name MUST be an empty sequence and the subjectAltName extension
// MUST be critical.
// This code assumes that criticality condition is checked by the caller, and
// therefore only needs to avoid the IsPermittedDirectoryName check against an
// empty subject in such a case.
if (subject_alt_names && subject_rdn_sequence.Length() == 0)
return;
if (!IsPermittedDirectoryName(subject_rdn_sequence)) {
errors->AddError(cert_errors::kNotPermittedByNameConstraints);
return;
}
}
bool NameConstraints::IsPermittedDNSName(std::string_view name) const {
for (const auto& excluded_name : excluded_subtrees_.dns_names) {
// When matching wildcard hosts against excluded subtrees, consider it a
// match if the constraint would match any expansion of the wildcard. Eg,
// *.bar.com should match a constraint of foo.bar.com.
if (DNSNameMatches(name, excluded_name, WILDCARD_PARTIAL_MATCH))
return false;
}
// If permitted subtrees are not constrained, any name that is not excluded is
// allowed.
if (!(permitted_subtrees_.present_name_types & GENERAL_NAME_DNS_NAME))
return true;
for (const auto& permitted_name : permitted_subtrees_.dns_names) {
// When matching wildcard hosts against permitted subtrees, consider it a
// match only if the constraint would match all expansions of the wildcard.
// Eg, *.bar.com should match a constraint of bar.com, but not foo.bar.com.
if (DNSNameMatches(name, permitted_name, WILDCARD_FULL_MATCH))
return true;
}
return false;
}
bool NameConstraints::IsPermittedDirectoryName(
const der::Input& name_rdn_sequence) const {
for (const auto& excluded_name : excluded_subtrees_.directory_names) {
if (VerifyNameInSubtree(name_rdn_sequence, excluded_name))
return false;
}
// If permitted subtrees are not constrained, any name that is not excluded is
// allowed.
if (!(permitted_subtrees_.present_name_types & GENERAL_NAME_DIRECTORY_NAME))
return true;
for (const auto& permitted_name : permitted_subtrees_.directory_names) {
if (VerifyNameInSubtree(name_rdn_sequence, permitted_name))
return true;
}
return false;
}
bool NameConstraints::IsPermittedIP(const IPAddress& ip) const {
for (const auto& excluded_ip : excluded_subtrees_.ip_address_ranges) {
if (IPAddressMatchesPrefix(ip, excluded_ip.first, excluded_ip.second))
return false;
}
// If permitted subtrees are not constrained, any name that is not excluded is
// allowed.
if (!(permitted_subtrees_.present_name_types & GENERAL_NAME_IP_ADDRESS))
return true;
for (const auto& permitted_ip : permitted_subtrees_.ip_address_ranges) {
if (IPAddressMatchesPrefix(ip, permitted_ip.first, permitted_ip.second))
return true;
}
return false;
}
} // namespace net