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Rewrite name constraints matching with CBS.

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See also 8393de42498f8be75cf0353f5c9f906a43a748d2 from upstream and
CBS-2021-3712. But rather than do that, I've rewritten it with CBS, so
it's a bit clearer. The previous commit added tests.

Change-Id: Ie52e28f07b9bf805c8730eab7be5d40cb5d558b6
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/49008
Reviewed-by: Adam Langley <agl@google.com>
chromium-5359
David Benjamin 4 years ago committed by Adam Langley
parent 04601b026a
commit b27438e126
5 changed files with 149 additions and 55 deletions
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  1. 22
      crypto/bytestring/bytestring_test.cc
  2. 8
      crypto/bytestring/cbs.c
  3. 3
      crypto/x509/x509_test.cc
  4. 166
      crypto/x509v3/v3_ncons.c
  5. 5
      include/openssl/bytestring.h

22
crypto/bytestring/bytestring_test.cc
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@ -115,6 +115,28 @@ TEST(CBSTest, GetPrefixedBad) {
EXPECT_FALSE(CBS_get_u24_length_prefixed(&data, &prefixed));
}
TEST(CBSTest, GetUntilFirst) {
static const uint8_t kData[] = {0, 1, 2, 3, 0, 1, 2, 3};
CBS data;
CBS_init(&data, kData, sizeof(kData));
CBS prefix;
EXPECT_FALSE(CBS_get_until_first(&data, &prefix, 4));
EXPECT_EQ(CBS_data(&data), kData);
EXPECT_EQ(CBS_len(&data), sizeof(kData));
ASSERT_TRUE(CBS_get_until_first(&data, &prefix, 0));
EXPECT_EQ(CBS_len(&prefix), 0u);
EXPECT_EQ(CBS_data(&data), kData);
EXPECT_EQ(CBS_len(&data), sizeof(kData));
ASSERT_TRUE(CBS_get_until_first(&data, &prefix, 2));
EXPECT_EQ(CBS_data(&prefix), kData);
EXPECT_EQ(CBS_len(&prefix), 2u);
EXPECT_EQ(CBS_data(&data), kData + 2);
EXPECT_EQ(CBS_len(&data), sizeof(kData) - 2);
}
TEST(CBSTest, GetASN1) {
static const uint8_t kData1[] = {0x30, 2, 1, 2};
static const uint8_t kData2[] = {0x30, 3, 1, 2};

8
crypto/bytestring/cbs.c
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@ -216,6 +216,14 @@ int CBS_get_u24_length_prefixed(CBS *cbs, CBS *out) {
return cbs_get_length_prefixed(cbs, out, 3);
}
int CBS_get_until_first(CBS *cbs, CBS *out, uint8_t c) {
const uint8_t *split = OPENSSL_memchr(CBS_data(cbs), c, CBS_len(cbs));
if (split == NULL) {
return 0;
}
return CBS_get_bytes(cbs, out, split - CBS_data(cbs));
}
// parse_base128_integer reads a big-endian base-128 integer from |cbs| and sets
// |*out| to the result. This is the encoding used in DER for both high tag
// number form and OID components.

3
crypto/x509/x509_test.cc
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@ -1557,6 +1557,9 @@ TEST(X509Test, NameConstraints) {
X509_V_ERR_PERMITTED_VIOLATION},
{GEN_DNS, "foo.example.com", ".unrelated.much.longer.name.example",
X509_V_ERR_PERMITTED_VIOLATION},
// NUL bytes, if not rejected, should not confuse the matching logic.
{GEN_DNS, std::string({'a', '\0', 'a'}), std::string({'a', '\0', 'b'}),
X509_V_ERR_PERMITTED_VIOLATION},
// Names must be emails.
{GEN_EMAIL, "not-an-email.example", "not-an-email.example",

166
crypto/x509v3/v3_ncons.c
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@ -389,25 +389,73 @@ static int nc_dn(X509_NAME *nm, X509_NAME *base)
return X509_V_OK;
}
static int starts_with(const CBS *cbs, uint8_t c)
{
return CBS_len(cbs) > 0 && CBS_data(cbs)[0] == c;
}
static int equal_case(const CBS *a, const CBS *b)
{
if (CBS_len(a) != CBS_len(b)) {
return 0;
}
/* Note we cannot use |OPENSSL_strncasecmp| because that would stop
* iterating at NUL. */
const uint8_t *a_data = CBS_data(a), *b_data = CBS_data(b);
for (size_t i = 0; i < CBS_len(a); i++) {
if (OPENSSL_tolower(a_data[i]) != OPENSSL_tolower(b_data[i])) {
return 0;
}
}
return 1;
}
static int has_suffix_case(const CBS *a, const CBS *b)
{
if (CBS_len(a) < CBS_len(b)) {
return 0;
}
CBS copy = *a;
CBS_skip(&copy, CBS_len(a) - CBS_len(b));
return equal_case(&copy, b);
}
static int nc_dns(ASN1_IA5STRING *dns, ASN1_IA5STRING *base)
{
char *baseptr = (char *)base->data;
char *dnsptr = (char *)dns->data;
CBS dns_cbs, base_cbs;
CBS_init(&dns_cbs, dns->data, dns->length);
CBS_init(&base_cbs, base->data, base->length);
/* Empty matches everything */
if (!*baseptr)
if (CBS_len(&base_cbs) == 0) {
return X509_V_OK;
}
/* If |base_cbs| begins with a '.', do a simple suffix comparison. This is
* not part of RFC5280, but is part of OpenSSL's original behavior. */
if (starts_with(&base_cbs, '.')) {
if (has_suffix_case(&dns_cbs, &base_cbs)) {
return X509_V_OK;
}
return X509_V_ERR_PERMITTED_VIOLATION;
}
/*
* Otherwise can add zero or more components on the left so compare RHS
* and if dns is longer and expect '.' as preceding character.
*/
if (dns->length > base->length) {
dnsptr += dns->length - base->length;
if (*baseptr != '.' && dnsptr[-1] != '.')
if (CBS_len(&dns_cbs) > CBS_len(&base_cbs)) {
uint8_t dot;
if (!CBS_skip(&dns_cbs, CBS_len(&dns_cbs) - CBS_len(&base_cbs) - 1) ||
!CBS_get_u8(&dns_cbs, &dot) ||
dot != '.') {
return X509_V_ERR_PERMITTED_VIOLATION;
}
}
if (OPENSSL_strcasecmp(baseptr, dnsptr))
if (!equal_case(&dns_cbs, &base_cbs)) {
return X509_V_ERR_PERMITTED_VIOLATION;
}
return X509_V_OK;
@ -415,86 +463,94 @@ static int nc_dns(ASN1_IA5STRING *dns, ASN1_IA5STRING *base)
static int nc_email(ASN1_IA5STRING *eml, ASN1_IA5STRING *base)
{
const char *baseptr = (char *)base->data;
const char *emlptr = (char *)eml->data;
const char *baseat = strchr(baseptr, '@');
const char *emlat = strchr(emlptr, '@');
if (!emlat)
CBS eml_cbs, base_cbs;
CBS_init(&eml_cbs, eml->data, eml->length);
CBS_init(&base_cbs, base->data, base->length);
/* TODO(davidben): In OpenSSL 1.1.1, this switched from the first '@' to the
* last one. Match them here, or perhaps do an actual parse. Looks like
* multiple '@'s may be allowed in quoted strings. */
CBS eml_local, base_local;
if (!CBS_get_until_first(&eml_cbs, &eml_local, '@')) {
return X509_V_ERR_UNSUPPORTED_NAME_SYNTAX;
}
int base_has_at = CBS_get_until_first(&base_cbs, &base_local, '@');
/* Special case: inital '.' is RHS match */
if (!baseat && (*baseptr == '.')) {
if (eml->length > base->length) {
emlptr += eml->length - base->length;
if (!OPENSSL_strcasecmp(baseptr, emlptr))
return X509_V_OK;
if (!base_has_at && starts_with(&base_cbs, '.')) {
if (has_suffix_case(&eml_cbs, &base_cbs)) {
return X509_V_OK;
}
return X509_V_ERR_PERMITTED_VIOLATION;
}
/* If we have anything before '@' match local part */
if (baseat) {
if (baseat != baseptr) {
if ((baseat - baseptr) != (emlat - emlptr))
return X509_V_ERR_PERMITTED_VIOLATION;
if (base_has_at) {
/* TODO(davidben): This interprets a constraint of "@example.com" as
* "example.com", which is not part of RFC5280. */
if (CBS_len(&base_local) > 0) {
/* Case sensitive match of local part */
if (strncmp(baseptr, emlptr, emlat - emlptr))
if (!CBS_mem_equal(&base_local, CBS_data(&eml_local),
CBS_len(&eml_local))) {
return X509_V_ERR_PERMITTED_VIOLATION;
}
}
/* Position base after '@' */
baseptr = baseat + 1;
assert(starts_with(&base_cbs, '@'));
CBS_skip(&base_cbs, 1);
}
emlptr = emlat + 1;
/* Just have hostname left to match: case insensitive */
if (OPENSSL_strcasecmp(baseptr, emlptr))
assert(starts_with(&eml_cbs, '@'));
CBS_skip(&eml_cbs, 1);
if (!equal_case(&base_cbs, &eml_cbs)) {
return X509_V_ERR_PERMITTED_VIOLATION;
}
return X509_V_OK;
}
static int nc_uri(ASN1_IA5STRING *uri, ASN1_IA5STRING *base)
{
const char *baseptr = (char *)base->data;
const char *hostptr = (char *)uri->data;
const char *p = strchr(hostptr, ':');
int hostlen;
CBS uri_cbs, base_cbs;
CBS_init(&uri_cbs, uri->data, uri->length);
CBS_init(&base_cbs, base->data, base->length);
/* Check for foo:// and skip past it */
if (!p || (p[1] != '/') || (p[2] != '/'))
CBS scheme;
uint8_t byte;
if (!CBS_get_until_first(&uri_cbs, &scheme, ':') ||
!CBS_skip(&uri_cbs, 1) || // Skip the colon
!CBS_get_u8(&uri_cbs, &byte) || byte != '/' ||
!CBS_get_u8(&uri_cbs, &byte) || byte != '/') {
return X509_V_ERR_UNSUPPORTED_NAME_SYNTAX;
hostptr = p + 3;
/* Determine length of hostname part of URI */
/* Look for a port indicator as end of hostname first */
p = strchr(hostptr, ':');
/* Otherwise look for trailing slash */
if (!p)
p = strchr(hostptr, '/');
}
if (!p)
hostlen = strlen(hostptr);
else
hostlen = p - hostptr;
/* Look for a port indicator as end of hostname first. Otherwise look for
* trailing slash, or the end of the string.
* TODO(davidben): This is not a correct URI parser and mishandles IPv6
* literals. */
CBS host;
if (!CBS_get_until_first(&uri_cbs, &host, ':') &&
!CBS_get_until_first(&uri_cbs, &host, '/')) {
host = uri_cbs;
}
if (hostlen == 0)
if (CBS_len(&host) == 0) {
return X509_V_ERR_UNSUPPORTED_NAME_SYNTAX;
}
/* Special case: inital '.' is RHS match */
if (*baseptr == '.') {
if (hostlen > base->length) {
p = hostptr + hostlen - base->length;
if (!OPENSSL_strncasecmp(p, baseptr, base->length))
return X509_V_OK;
if (starts_with(&base_cbs, '.')) {
if (has_suffix_case(&host, &base_cbs)) {
return X509_V_OK;
}
return X509_V_ERR_PERMITTED_VIOLATION;
}
if ((base->length != (int)hostlen)
|| OPENSSL_strncasecmp(hostptr, baseptr, hostlen))
if (!equal_case(&base_cbs, &host)) {
return X509_V_ERR_PERMITTED_VIOLATION;
}
return X509_V_OK;

5
include/openssl/bytestring.h
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@ -154,6 +154,11 @@ OPENSSL_EXPORT int CBS_get_u16_length_prefixed(CBS *cbs, CBS *out);
// returns one on success and zero on error.
OPENSSL_EXPORT int CBS_get_u24_length_prefixed(CBS *cbs, CBS *out);
// CBS_get_until_first finds the first instance of |c| in |cbs|. If found, it
// sets |*out| to the text before the match, advances |cbs| over it, and returns
// one. Otherwise, it returns zero and leaves |cbs| unmodified.
OPENSSL_EXPORT int CBS_get_until_first(CBS *cbs, CBS *out, uint8_t c);
// Parsing ASN.1
//

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