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xemu/crypto/tlscredsx509.c
Daniel P. Berrange 9a2fd4347c crypto: add sanity checking of TLS x509 credentials 
If the administrator incorrectly sets up their x509 certificates,
the errors seen at runtime during connection attempts are very
obscure and difficult to diagnose. This has been a particular
problem for people using openssl to generate their certificates
instead of the gnutls certtool, because the openssl tools don't
turn on the various x509 extensions that gnutls expects to be
present by default.

This change thus adds support in the TLS credentials object to
sanity check the certificates when QEMU first loads them. This
gives the administrator immediate feedback for the majority of
common configuration mistakes, reducing the pain involved in
setting up TLS. The code is derived from equivalent code that
has been part of libvirt's TLS support and has been seen to be
valuable in assisting admins.

It is possible to disable the sanity checking, however, via
the new 'sanity-check' property on the tls-creds object type,
with a value of 'no'.

Unit tests are included in this change to verify the correctness
of the sanity checking code in all the key scenarios it is
intended to cope with. As part of the test suite, the pkix_asn1_tab.c
from gnutls is imported. This file is intentionally copied from the
(long since obsolete) gnutls 1.6.3 source tree, since that version
was still under GPLv2+, rather than the GPLv3+ of gnutls >= 2.0.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2015-09-15 15:05:09 +01:00

810 lines
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/*
* QEMU crypto TLS x509 credential support
*
* Copyright (c) 2015 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, see <http://www.gnu.org/licenses/>.
*
*/
#include "crypto/tlscredsx509.h"
#include "crypto/tlscredspriv.h"
#include "qom/object_interfaces.h"
#include "trace.h"
#ifdef CONFIG_GNUTLS
#include <gnutls/x509.h>
static int
qcrypto_tls_creds_check_cert_times(gnutls_x509_crt_t cert,
const char *certFile,
bool isServer,
bool isCA,
Error **errp)
{
time_t now = time(NULL);
if (now == ((time_t)-1)) {
error_setg_errno(errp, errno, "cannot get current time");
return -1;
}
if (gnutls_x509_crt_get_expiration_time(cert) < now) {
error_setg(errp,
(isCA ?
"The CA certificate %s has expired" :
(isServer ?
"The server certificate %s has expired" :
"The client certificate %s has expired")),
certFile);
return -1;
}
if (gnutls_x509_crt_get_activation_time(cert) > now) {
error_setg(errp,
(isCA ?
"The CA certificate %s is not yet active" :
(isServer ?
"The server certificate %s is not yet active" :
"The client certificate %s is not yet active")),
certFile);
return -1;
}
return 0;
}
#if LIBGNUTLS_VERSION_NUMBER >= 2
/*
* The gnutls_x509_crt_get_basic_constraints function isn't
* available in GNUTLS 1.0.x branches. This isn't critical
* though, since gnutls_certificate_verify_peers2 will do
* pretty much the same check at runtime, so we can just
* disable this code
*/
static int
qcrypto_tls_creds_check_cert_basic_constraints(QCryptoTLSCredsX509 *creds,
gnutls_x509_crt_t cert,
const char *certFile,
bool isServer,
bool isCA,
Error **errp)
{
int status;
status = gnutls_x509_crt_get_basic_constraints(cert, NULL, NULL, NULL);
trace_qcrypto_tls_creds_x509_check_basic_constraints(
creds, certFile, status);
if (status > 0) { /* It is a CA cert */
if (!isCA) {
error_setg(errp, isServer ?
"The certificate %s basic constraints show a CA, "
"but we need one for a server" :
"The certificate %s basic constraints show a CA, "
"but we need one for a client",
certFile);
return -1;
}
} else if (status == 0) { /* It is not a CA cert */
if (isCA) {
error_setg(errp,
"The certificate %s basic constraints do not "
"show a CA",
certFile);
return -1;
}
} else if (status == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE) {
/* Missing basicConstraints */
if (isCA) {
error_setg(errp,
"The certificate %s is missing basic constraints "
"for a CA",
certFile);
return -1;
}
} else { /* General error */
error_setg(errp,
"Unable to query certificate %s basic constraints: %s",
certFile, gnutls_strerror(status));
return -1;
}
return 0;
}
#endif
static int
qcrypto_tls_creds_check_cert_key_usage(QCryptoTLSCredsX509 *creds,
gnutls_x509_crt_t cert,
const char *certFile,
bool isCA,
Error **errp)
{
int status;
unsigned int usage = 0;
unsigned int critical = 0;
status = gnutls_x509_crt_get_key_usage(cert, &usage, &critical);
trace_qcrypto_tls_creds_x509_check_key_usage(
creds, certFile, status, usage, critical);
if (status < 0) {
if (status == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE) {
usage = isCA ? GNUTLS_KEY_KEY_CERT_SIGN :
GNUTLS_KEY_DIGITAL_SIGNATURE|GNUTLS_KEY_KEY_ENCIPHERMENT;
} else {
error_setg(errp,
"Unable to query certificate %s key usage: %s",
certFile, gnutls_strerror(status));
return -1;
}
}
if (isCA) {
if (!(usage & GNUTLS_KEY_KEY_CERT_SIGN)) {
if (critical) {
error_setg(errp,
"Certificate %s usage does not permit "
"certificate signing", certFile);
return -1;
}
}
} else {
if (!(usage & GNUTLS_KEY_DIGITAL_SIGNATURE)) {
if (critical) {
error_setg(errp,
"Certificate %s usage does not permit digital "
"signature", certFile);
return -1;
}
}
if (!(usage & GNUTLS_KEY_KEY_ENCIPHERMENT)) {
if (critical) {
error_setg(errp,
"Certificate %s usage does not permit key "
"encipherment", certFile);
return -1;
}
}
}
return 0;
}
static int
qcrypto_tls_creds_check_cert_key_purpose(QCryptoTLSCredsX509 *creds,
gnutls_x509_crt_t cert,
const char *certFile,
bool isServer,
Error **errp)
{
int status;
size_t i;
unsigned int purposeCritical;
unsigned int critical;
char *buffer = NULL;
size_t size;
bool allowClient = false, allowServer = false;
critical = 0;
for (i = 0; ; i++) {
size = 0;
status = gnutls_x509_crt_get_key_purpose_oid(cert, i, buffer,
&size, NULL);
if (status == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE) {
/* If there is no data at all, then we must allow
client/server to pass */
if (i == 0) {
allowServer = allowClient = true;
}
break;
}
if (status != GNUTLS_E_SHORT_MEMORY_BUFFER) {
error_setg(errp,
"Unable to query certificate %s key purpose: %s",
certFile, gnutls_strerror(status));
return -1;
}
buffer = g_new0(char, size);
status = gnutls_x509_crt_get_key_purpose_oid(cert, i, buffer,
&size, &purposeCritical);
if (status < 0) {
trace_qcrypto_tls_creds_x509_check_key_purpose(
creds, certFile, status, "<none>", purposeCritical);
g_free(buffer);
error_setg(errp,
"Unable to query certificate %s key purpose: %s",
certFile, gnutls_strerror(status));
return -1;
}
trace_qcrypto_tls_creds_x509_check_key_purpose(
creds, certFile, status, buffer, purposeCritical);
if (purposeCritical) {
critical = true;
}
if (g_str_equal(buffer, GNUTLS_KP_TLS_WWW_SERVER)) {
allowServer = true;
} else if (g_str_equal(buffer, GNUTLS_KP_TLS_WWW_CLIENT)) {
allowClient = true;
} else if (g_str_equal(buffer, GNUTLS_KP_ANY)) {
allowServer = allowClient = true;
}
g_free(buffer);
}
if (isServer) {
if (!allowServer) {
if (critical) {
error_setg(errp,
"Certificate %s purpose does not allow "
"use with a TLS server", certFile);
return -1;
}
}
} else {
if (!allowClient) {
if (critical) {
error_setg(errp,
"Certificate %s purpose does not allow use "
"with a TLS client", certFile);
return -1;
}
}
}
return 0;
}
static int
qcrypto_tls_creds_check_cert(QCryptoTLSCredsX509 *creds,
gnutls_x509_crt_t cert,
const char *certFile,
bool isServer,
bool isCA,
Error **errp)
{
if (qcrypto_tls_creds_check_cert_times(cert, certFile,
isServer, isCA,
errp) < 0) {
return -1;
}
#if LIBGNUTLS_VERSION_NUMBER >= 2
if (qcrypto_tls_creds_check_cert_basic_constraints(creds,
cert, certFile,
isServer, isCA,
errp) < 0) {
return -1;
}
#endif
if (qcrypto_tls_creds_check_cert_key_usage(creds,
cert, certFile,
isCA, errp) < 0) {
return -1;
}
if (!isCA &&
qcrypto_tls_creds_check_cert_key_purpose(creds,
cert, certFile,
isServer, errp) < 0) {
return -1;
}
return 0;
}
static int
qcrypto_tls_creds_check_cert_pair(gnutls_x509_crt_t cert,
const char *certFile,
gnutls_x509_crt_t *cacerts,
size_t ncacerts,
const char *cacertFile,
bool isServer,
Error **errp)
{
unsigned int status;
if (gnutls_x509_crt_list_verify(&cert, 1,
cacerts, ncacerts,
NULL, 0,
0, &status) < 0) {
error_setg(errp, isServer ?
"Unable to verify server certificate %s against "
"CA certificate %s" :
"Unable to verify client certificate %s against "
"CA certificate %s",
certFile, cacertFile);
return -1;
}
if (status != 0) {
const char *reason = "Invalid certificate";
if (status & GNUTLS_CERT_INVALID) {
reason = "The certificate is not trusted";
}
if (status & GNUTLS_CERT_SIGNER_NOT_FOUND) {
reason = "The certificate hasn't got a known issuer";
}
if (status & GNUTLS_CERT_REVOKED) {
reason = "The certificate has been revoked";
}
#ifndef GNUTLS_1_0_COMPAT
if (status & GNUTLS_CERT_INSECURE_ALGORITHM) {
reason = "The certificate uses an insecure algorithm";
}
#endif
error_setg(errp,
"Our own certificate %s failed validation against %s: %s",
certFile, cacertFile, reason);
return -1;
}
return 0;
}
static gnutls_x509_crt_t
qcrypto_tls_creds_load_cert(QCryptoTLSCredsX509 *creds,
const char *certFile,
bool isServer,
Error **errp)
{
gnutls_datum_t data;
gnutls_x509_crt_t cert = NULL;
char *buf = NULL;
gsize buflen;
GError *gerr;
int ret = -1;
trace_qcrypto_tls_creds_x509_load_cert(creds, isServer, certFile);
if (gnutls_x509_crt_init(&cert) < 0) {
error_setg(errp, "Unable to initialize certificate");
goto cleanup;
}
if (!g_file_get_contents(certFile, &buf, &buflen, &gerr)) {
error_setg(errp, "Cannot load CA cert list %s: %s",
certFile, gerr->message);
g_error_free(gerr);
goto cleanup;
}
data.data = (unsigned char *)buf;
data.size = strlen(buf);
if (gnutls_x509_crt_import(cert, &data, GNUTLS_X509_FMT_PEM) < 0) {
error_setg(errp, isServer ?
"Unable to import server certificate %s" :
"Unable to import client certificate %s",
certFile);
goto cleanup;
}
ret = 0;
cleanup:
if (ret != 0) {
gnutls_x509_crt_deinit(cert);
cert = NULL;
}
g_free(buf);
return cert;
}
static int
qcrypto_tls_creds_load_ca_cert_list(QCryptoTLSCredsX509 *creds,
const char *certFile,
gnutls_x509_crt_t *certs,
unsigned int certMax,
size_t *ncerts,
Error **errp)
{
gnutls_datum_t data;
char *buf = NULL;
gsize buflen;
int ret = -1;
GError *gerr = NULL;
*ncerts = 0;
trace_qcrypto_tls_creds_x509_load_cert_list(creds, certFile);
if (!g_file_get_contents(certFile, &buf, &buflen, &gerr)) {
error_setg(errp, "Cannot load CA cert list %s: %s",
certFile, gerr->message);
g_error_free(gerr);
goto cleanup;
}
data.data = (unsigned char *)buf;
data.size = strlen(buf);
if (gnutls_x509_crt_list_import(certs, &certMax, &data,
GNUTLS_X509_FMT_PEM, 0) < 0) {
error_setg(errp,
"Unable to import CA certificate list %s",
certFile);
goto cleanup;
}
*ncerts = certMax;
ret = 0;
cleanup:
g_free(buf);
return ret;
}
#define MAX_CERTS 16
static int
qcrypto_tls_creds_x509_sanity_check(QCryptoTLSCredsX509 *creds,
bool isServer,
const char *cacertFile,
const char *certFile,
Error **errp)
{
gnutls_x509_crt_t cert = NULL;
gnutls_x509_crt_t cacerts[MAX_CERTS];
size_t ncacerts = 0;
size_t i;
int ret = -1;
memset(cacerts, 0, sizeof(cacerts));
if (access(certFile, R_OK) == 0) {
cert = qcrypto_tls_creds_load_cert(creds,
certFile, isServer,
errp);
if (!cert) {
goto cleanup;
}
}
if (access(cacertFile, R_OK) == 0) {
if (qcrypto_tls_creds_load_ca_cert_list(creds,
cacertFile, cacerts,
MAX_CERTS, &ncacerts,
errp) < 0) {
goto cleanup;
}
}
if (cert &&
qcrypto_tls_creds_check_cert(creds,
cert, certFile, isServer,
false, errp) < 0) {
goto cleanup;
}
for (i = 0; i < ncacerts; i++) {
if (qcrypto_tls_creds_check_cert(creds,
cacerts[i], cacertFile,
isServer, true, errp) < 0) {
goto cleanup;
}
}
if (cert && ncacerts &&
qcrypto_tls_creds_check_cert_pair(cert, certFile, cacerts,
ncacerts, cacertFile,
isServer, errp) < 0) {
goto cleanup;
}
ret = 0;
cleanup:
if (cert) {
gnutls_x509_crt_deinit(cert);
}
for (i = 0; i < ncacerts; i++) {
gnutls_x509_crt_deinit(cacerts[i]);
}
return ret;
}
static int
qcrypto_tls_creds_x509_load(QCryptoTLSCredsX509 *creds,
Error **errp)
{
char *cacert = NULL, *cacrl = NULL, *cert = NULL,
*key = NULL, *dhparams = NULL;
int ret;
int rv = -1;
trace_qcrypto_tls_creds_x509_load(creds,
creds->parent_obj.dir ? creds->parent_obj.dir : "<nodir>");
if (creds->parent_obj.endpoint == QCRYPTO_TLS_CREDS_ENDPOINT_SERVER) {
if (qcrypto_tls_creds_get_path(&creds->parent_obj,
QCRYPTO_TLS_CREDS_X509_CA_CERT,
true, &cacert, errp) < 0 ||
qcrypto_tls_creds_get_path(&creds->parent_obj,
QCRYPTO_TLS_CREDS_X509_CA_CRL,
false, &cacrl, errp) < 0 ||
qcrypto_tls_creds_get_path(&creds->parent_obj,
QCRYPTO_TLS_CREDS_X509_SERVER_CERT,
true, &cert, errp) < 0 ||
qcrypto_tls_creds_get_path(&creds->parent_obj,
QCRYPTO_TLS_CREDS_X509_SERVER_KEY,
true, &key, errp) < 0 ||
qcrypto_tls_creds_get_path(&creds->parent_obj,
QCRYPTO_TLS_CREDS_DH_PARAMS,
false, &dhparams, errp) < 0) {
goto cleanup;
}
} else {
if (qcrypto_tls_creds_get_path(&creds->parent_obj,
QCRYPTO_TLS_CREDS_X509_CA_CERT,
true, &cacert, errp) < 0 ||
qcrypto_tls_creds_get_path(&creds->parent_obj,
QCRYPTO_TLS_CREDS_X509_CLIENT_CERT,
false, &cert, errp) < 0 ||
qcrypto_tls_creds_get_path(&creds->parent_obj,
QCRYPTO_TLS_CREDS_X509_CLIENT_KEY,
false, &key, errp) < 0) {
goto cleanup;
}
}
if (creds->sanityCheck &&
qcrypto_tls_creds_x509_sanity_check(creds,
creds->parent_obj.endpoint == QCRYPTO_TLS_CREDS_ENDPOINT_SERVER,
cacert, cert, errp) < 0) {
goto cleanup;
}
ret = gnutls_certificate_allocate_credentials(&creds->data);
if (ret < 0) {
error_setg(errp, "Cannot allocate credentials: '%s'",
gnutls_strerror(ret));
goto cleanup;
}
ret = gnutls_certificate_set_x509_trust_file(creds->data,
cacert,
GNUTLS_X509_FMT_PEM);
if (ret < 0) {
error_setg(errp, "Cannot load CA certificate '%s': %s",
cacert, gnutls_strerror(ret));
goto cleanup;
}
if (cert != NULL && key != NULL) {
ret = gnutls_certificate_set_x509_key_file(creds->data,
cert, key,
GNUTLS_X509_FMT_PEM);
if (ret < 0) {
error_setg(errp, "Cannot load certificate '%s' & key '%s': %s",
cert, key, gnutls_strerror(ret));
goto cleanup;
}
}
if (cacrl != NULL) {
ret = gnutls_certificate_set_x509_crl_file(creds->data,
cacrl,
GNUTLS_X509_FMT_PEM);
if (ret < 0) {
error_setg(errp, "Cannot load CRL '%s': %s",
cacrl, gnutls_strerror(ret));
goto cleanup;
}
}
if (creds->parent_obj.endpoint == QCRYPTO_TLS_CREDS_ENDPOINT_SERVER) {
if (qcrypto_tls_creds_get_dh_params_file(&creds->parent_obj, dhparams,
&creds->parent_obj.dh_params,
errp) < 0) {
goto cleanup;
}
gnutls_certificate_set_dh_params(creds->data,
creds->parent_obj.dh_params);
}
rv = 0;
cleanup:
g_free(cacert);
g_free(cacrl);
g_free(cert);
g_free(key);
g_free(dhparams);
return rv;
}
static void
qcrypto_tls_creds_x509_unload(QCryptoTLSCredsX509 *creds)
{
if (creds->data) {
gnutls_certificate_free_credentials(creds->data);
creds->data = NULL;
}
}
#else /* ! CONFIG_GNUTLS */
static void
qcrypto_tls_creds_x509_load(QCryptoTLSCredsX509 *creds G_GNUC_UNUSED,
Error **errp)
{
error_setg(errp, "TLS credentials support requires GNUTLS");
}
static void
qcrypto_tls_creds_x509_unload(QCryptoTLSCredsX509 *creds G_GNUC_UNUSED)
{
/* nada */
}
#endif /* ! CONFIG_GNUTLS */
static void
qcrypto_tls_creds_x509_prop_set_loaded(Object *obj,
bool value,
Error **errp)
{
QCryptoTLSCredsX509 *creds = QCRYPTO_TLS_CREDS_X509(obj);
if (value) {
qcrypto_tls_creds_x509_load(creds, errp);
} else {
qcrypto_tls_creds_x509_unload(creds);
}
}
#ifdef CONFIG_GNUTLS
static bool
qcrypto_tls_creds_x509_prop_get_loaded(Object *obj,
Error **errp G_GNUC_UNUSED)
{
QCryptoTLSCredsX509 *creds = QCRYPTO_TLS_CREDS_X509(obj);
return creds->data != NULL;
}
#else /* ! CONFIG_GNUTLS */
static bool
qcrypto_tls_creds_x509_prop_get_loaded(Object *obj G_GNUC_UNUSED,
Error **errp G_GNUC_UNUSED)
{
return false;
}
#endif /* ! CONFIG_GNUTLS */
static void
qcrypto_tls_creds_x509_prop_set_sanity(Object *obj,
bool value,
Error **errp G_GNUC_UNUSED)
{
QCryptoTLSCredsX509 *creds = QCRYPTO_TLS_CREDS_X509(obj);
creds->sanityCheck = value;
}
static bool
qcrypto_tls_creds_x509_prop_get_sanity(Object *obj,
Error **errp G_GNUC_UNUSED)
{
QCryptoTLSCredsX509 *creds = QCRYPTO_TLS_CREDS_X509(obj);
return creds->sanityCheck;
}
static void
qcrypto_tls_creds_x509_complete(UserCreatable *uc, Error **errp)
{
object_property_set_bool(OBJECT(uc), true, "loaded", errp);
}
static void
qcrypto_tls_creds_x509_init(Object *obj)
{
QCryptoTLSCredsX509 *creds = QCRYPTO_TLS_CREDS_X509(obj);
creds->sanityCheck = true;
object_property_add_bool(obj, "loaded",
qcrypto_tls_creds_x509_prop_get_loaded,
qcrypto_tls_creds_x509_prop_set_loaded,
NULL);
object_property_add_bool(obj, "sanity-check",
qcrypto_tls_creds_x509_prop_get_sanity,
qcrypto_tls_creds_x509_prop_set_sanity,
NULL);
}
static void
qcrypto_tls_creds_x509_finalize(Object *obj)
{
QCryptoTLSCredsX509 *creds = QCRYPTO_TLS_CREDS_X509(obj);
qcrypto_tls_creds_x509_unload(creds);
}
static void
qcrypto_tls_creds_x509_class_init(ObjectClass *oc, void *data)
{
UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
ucc->complete = qcrypto_tls_creds_x509_complete;
}
static const TypeInfo qcrypto_tls_creds_x509_info = {
.parent = TYPE_QCRYPTO_TLS_CREDS,
.name = TYPE_QCRYPTO_TLS_CREDS_X509,
.instance_size = sizeof(QCryptoTLSCredsX509),
.instance_init = qcrypto_tls_creds_x509_init,
.instance_finalize = qcrypto_tls_creds_x509_finalize,
.class_size = sizeof(QCryptoTLSCredsX509Class),
.class_init = qcrypto_tls_creds_x509_class_init,
.interfaces = (InterfaceInfo[]) {
{ TYPE_USER_CREATABLE },
{ }
}
};
static void
qcrypto_tls_creds_x509_register_types(void)
{
type_register_static(&qcrypto_tls_creds_x509_info);
}
type_init(qcrypto_tls_creds_x509_register_types);
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