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>

1 files changed, 485 insertions, 0 deletions

diff --git a/tests/crypto-tls-x509-helpers.c b/tests/crypto-tls-x509-helpers.c
new file mode 100644
index 0000000000..c5de67baaf
--- /dev/null
+++ b/tests/crypto-tls-x509-helpers.c
@@ -0,0 +1,485 @@
+/*
+ * 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 2.1 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/>.
+ *
+ * Author: Daniel P. Berrange <berrange@redhat.com>
+ */
+
+#include <stdlib.h>
+#include <fcntl.h>
+
+#include "config-host.h"
+#include "crypto-tls-x509-helpers.h"
+#include "qemu/sockets.h"
+
+#ifdef QCRYPTO_HAVE_TLS_TEST_SUPPORT
+
+/*
+ * This stores some static data that is needed when
+ * encoding extensions in the x509 certs
+ */
+ASN1_TYPE pkix_asn1;
+
+/*
+ * To avoid consuming random entropy to generate keys,
+ * here's one we prepared earlier :-)
+ */
+gnutls_x509_privkey_t privkey;
+# define PRIVATE_KEY                                              \
+    "-----BEGIN PRIVATE KEY-----\n"                               \
+    "MIICdQIBADANBgkqhkiG9w0BAQEFAASCAl8wggJbAgEAAoGBALVcr\n"     \
+    "BL40Tm6yq88FBhJNw1aaoCjmtg0l4dWQZ/e9Fimx4ARxFpT+ji4FE\n"     \
+    "Cgl9s/SGqC+1nvlkm9ViSo0j7MKDbnDB+VRHDvMAzQhA2X7e8M0n9\n"     \
+    "rPolUY2lIVC83q0BBaOBkCj2RSmT2xTEbbC2xLukSrg2WP/ihVOxc\n"     \
+    "kXRuyFtzAgMBAAECgYB7slBexDwXrtItAMIH6m/U+LUpNe0Xx48OL\n"     \
+    "IOn4a4whNgO/o84uIwygUK27ZGFZT0kAGAk8CdF9hA6ArcbQ62s1H\n"     \
+    "myxrUbF9/mrLsQw1NEqpuUk9Ay2Tx5U/wPx35S3W/X2AvR/ZpTnCn\n"     \
+    "2q/7ym9fyiSoj86drD7BTvmKXlOnOwQJBAPOFMp4mMa9NGpGuEssO\n"     \
+    "m3Uwbp6lhcP0cA9MK+iOmeANpoKWfBdk5O34VbmeXnGYWEkrnX+9J\n"     \
+    "bM4wVhnnBWtgBMCQQC+qAEmvwcfhauERKYznMVUVksyeuhxhCe7EK\n"     \
+    "mPh+U2+g0WwdKvGDgO0PPt1gq0ILEjspMDeMHVdTwkaVBo/uMhAkA\n"     \
+    "Z5SsZyCP2aTOPFDypXRdI4eqRcjaEPOUBq27r3uYb/jeboVb2weLa\n"     \
+    "L1MmVuHiIHoa5clswPdWVI2y0em2IGoDAkBPSp/v9VKJEZabk9Frd\n"     \
+    "a+7u4fanrM9QrEjY3KhduslSilXZZSxrWjjAJPyPiqFb3M8XXA26W\n"     \
+    "nz1KYGnqYKhLcBAkB7dt57n9xfrhDpuyVEv+Uv1D3VVAhZlsaZ5Pp\n"     \
+    "dcrhrkJn2sa/+O8OKvdrPSeeu/N5WwYhJf61+CPoenMp7IFci\n"         \
+    "-----END PRIVATE KEY-----\n"
+
+/*
+ * This loads the private key we defined earlier
+ */
+static gnutls_x509_privkey_t test_tls_load_key(void)
+{
+    gnutls_x509_privkey_t key;
+    const gnutls_datum_t data = { (unsigned char *)PRIVATE_KEY,
+                                  strlen(PRIVATE_KEY) };
+    int err;
+
+    err = gnutls_x509_privkey_init(&key);
+    if (err < 0) {
+        g_critical("Failed to init key %s", gnutls_strerror(err));
+        abort();
+    }
+
+    err = gnutls_x509_privkey_import(key, &data,
+                                     GNUTLS_X509_FMT_PEM);
+    if (err < 0) {
+        if (err != GNUTLS_E_BASE64_UNEXPECTED_HEADER_ERROR &&
+            err != GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE) {
+            g_critical("Failed to import key %s", gnutls_strerror(err));
+            abort();
+        }
+
+        err = gnutls_x509_privkey_import_pkcs8(
+            key, &data, GNUTLS_X509_FMT_PEM, NULL, 0);
+        if (err < 0) {
+            g_critical("Failed to import PKCS8 key %s", gnutls_strerror(err));
+            abort();
+        }
+    }
+
+    return key;
+}
+
+
+void test_tls_init(const char *keyfile)
+{
+    gnutls_global_init();
+
+    if (asn1_array2tree(pkix_asn1_tab, &pkix_asn1, NULL) != ASN1_SUCCESS) {
+        abort();
+    }
+
+    privkey = test_tls_load_key();
+    if (!g_file_set_contents(keyfile, PRIVATE_KEY, -1, NULL)) {
+        abort();
+    }
+}
+
+
+void test_tls_cleanup(const char *keyfile)
+{
+    asn1_delete_structure(&pkix_asn1);
+    unlink(keyfile);
+}
+
+/*
+ * Turns an ASN1 object into a DER encoded byte array
+ */
+static void test_tls_der_encode(ASN1_TYPE src,
+                                const char *src_name,
+                                gnutls_datum_t *res)
+{
+  int size;
+  char *data = NULL;
+
+  size = 0;
+  asn1_der_coding(src, src_name, NULL, &size, NULL);
+
+  data = g_new0(char, size);
+
+  asn1_der_coding(src, src_name, data, &size, NULL);
+
+  res->data = (unsigned char *)data;
+  res->size = size;
+}
+
+
+static void
+test_tls_get_ipaddr(const char *addrstr,
+                    char **data,
+                    int *datalen)
+{
+    struct addrinfo *res;
+    struct addrinfo hints;
+
+    memset(&hints, 0, sizeof(hints));
+    hints.ai_flags = AI_NUMERICHOST;
+    g_assert(getaddrinfo(addrstr, NULL, &hints, &res) == 0);
+
+    *datalen = res->ai_addrlen;
+    *data = g_new(char, *datalen);
+    memcpy(*data, res->ai_addr, *datalen);
+}
+
+/*
+ * This is a fairly lame x509 certificate generator.
+ *
+ * Do not copy/use this code for generating real certificates
+ * since it leaves out many things that you would want in
+ * certificates for real world usage.
+ *
+ * This is good enough only for doing tests of the QEMU
+ * TLS certificate code
+ */
+void
+test_tls_generate_cert(QCryptoTLSTestCertReq *req,
+                       gnutls_x509_crt_t ca)
+{
+    gnutls_x509_crt_t crt;
+    int err;
+    static char buffer[1024 * 1024];
+    size_t size = sizeof(buffer);
+    char serial[5] = { 1, 2, 3, 4, 0 };
+    gnutls_datum_t der;
+    time_t start = time(NULL) + (60 * 60 * req->start_offset);
+    time_t expire = time(NULL) + (60 * 60 * (req->expire_offset
+                                             ? req->expire_offset : 24));
+
+    /*
+     * Prepare our new certificate object
+     */
+    err = gnutls_x509_crt_init(&crt);
+    if (err < 0) {
+        g_critical("Failed to initialize certificate %s", gnutls_strerror(err));
+        abort();
+    }
+    err = gnutls_x509_crt_set_key(crt, privkey);
+    if (err < 0) {
+        g_critical("Failed to set certificate key %s", gnutls_strerror(err));
+        abort();
+    }
+
+    /*
+     * A v3 certificate is required in order to be able
+     * set any of the basic constraints, key purpose and
+     * key usage data
+     */
+    gnutls_x509_crt_set_version(crt, 3);
+
+    if (req->country) {
+        err = gnutls_x509_crt_set_dn_by_oid(
+            crt, GNUTLS_OID_X520_COUNTRY_NAME, 0,
+            req->country, strlen(req->country));
+        if (err < 0) {
+            g_critical("Failed to set certificate country name %s",
+                       gnutls_strerror(err));
+            abort();
+        }
+    }
+    if (req->cn) {
+        err = gnutls_x509_crt_set_dn_by_oid(
+            crt, GNUTLS_OID_X520_COMMON_NAME, 0,
+            req->cn, strlen(req->cn));
+        if (err < 0) {
+            g_critical("Failed to set certificate common name %s",
+                       gnutls_strerror(err));
+            abort();
+        }
+    }
+
+    /*
+     * Setup the subject altnames, which are used
+     * for hostname checks in live sessions
+     */
+    if (req->altname1) {
+        err = gnutls_x509_crt_set_subject_alt_name(
+            crt, GNUTLS_SAN_DNSNAME,
+            req->altname1,
+            strlen(req->altname1),
+            GNUTLS_FSAN_APPEND);
+        if (err < 0) {
+            g_critical("Failed to set certificate alt name %s",
+                       gnutls_strerror(err));
+            abort();
+        }
+    }
+    if (req->altname2) {
+        err = gnutls_x509_crt_set_subject_alt_name(
+            crt, GNUTLS_SAN_DNSNAME,
+            req->altname2,
+            strlen(req->altname2),
+            GNUTLS_FSAN_APPEND);
+        if (err < 0) {
+            g_critical("Failed to set certificate %s alt name",
+                       gnutls_strerror(err));
+            abort();
+        }
+    }
+
+    /*
+     * IP address need to be put into the cert in their
+     * raw byte form, not strings, hence this is a little
+     * more complicated
+     */
+    if (req->ipaddr1) {
+        char *data;
+        int len;
+
+        test_tls_get_ipaddr(req->ipaddr1, &data, &len);
+
+        err = gnutls_x509_crt_set_subject_alt_name(
+            crt, GNUTLS_SAN_IPADDRESS,
+            data, len, GNUTLS_FSAN_APPEND);
+        if (err < 0) {
+            g_critical("Failed to set certificate alt name %s",
+                       gnutls_strerror(err));
+            abort();
+        }
+        g_free(data);
+    }
+    if (req->ipaddr2) {
+        char *data;
+        int len;
+
+        test_tls_get_ipaddr(req->ipaddr2, &data, &len);
+
+        err = gnutls_x509_crt_set_subject_alt_name(
+            crt, GNUTLS_SAN_IPADDRESS,
+            data, len, GNUTLS_FSAN_APPEND);
+        if (err < 0) {
+            g_critical("Failed to set certificate alt name %s",
+                       gnutls_strerror(err));
+            abort();
+        }
+        g_free(data);
+    }
+
+
+    /*
+     * Basic constraints are used to decide if the cert
+     * is for a CA or not. We can't use the convenient
+     * gnutls API for setting this, since it hardcodes
+     * the 'critical' field which we want control over
+     */
+    if (req->basicConstraintsEnable) {
+        ASN1_TYPE ext = ASN1_TYPE_EMPTY;
+
+        asn1_create_element(pkix_asn1, "PKIX1.BasicConstraints", &ext);
+        asn1_write_value(ext, "cA",
+                         req->basicConstraintsIsCA ? "TRUE" : "FALSE", 1);
+        asn1_write_value(ext, "pathLenConstraint", NULL, 0);
+        test_tls_der_encode(ext, "", &der);
+        err = gnutls_x509_crt_set_extension_by_oid(
+            crt, "2.5.29.19",
+            der.data, der.size,
+            req->basicConstraintsCritical);
+        if (err < 0) {
+            g_critical("Failed to set certificate basic constraints %s",
+                       gnutls_strerror(err));
+            g_free(der.data);
+            abort();
+        }
+        asn1_delete_structure(&ext);
+        g_free(der.data);
+    }
+
+    /*
+     * Next up the key usage extension. Again we can't
+     * use the gnutls API since it hardcodes the extension
+     * to be 'critical'
+     */
+    if (req->keyUsageEnable) {
+        ASN1_TYPE ext = ASN1_TYPE_EMPTY;
+        char str[2];
+
+        str[0] = req->keyUsageValue & 0xff;
+        str[1] = (req->keyUsageValue >> 8) & 0xff;
+
+        asn1_create_element(pkix_asn1, "PKIX1.KeyUsage", &ext);
+        asn1_write_value(ext, "", str, 9);
+        test_tls_der_encode(ext, "", &der);
+        err = gnutls_x509_crt_set_extension_by_oid(
+            crt, "2.5.29.15",
+            der.data, der.size,
+            req->keyUsageCritical);
+        if (err < 0) {
+            g_critical("Failed to set certificate key usage %s",
+                       gnutls_strerror(err));
+            g_free(der.data);
+            abort();
+        }
+        asn1_delete_structure(&ext);
+        g_free(der.data);
+    }
+
+    /*
+     * Finally the key purpose extension. This time
+     * gnutls has the opposite problem, always hardcoding
+     * it to be non-critical. So once again we have to
+     * set this the hard way building up ASN1 data ourselves
+     */
+    if (req->keyPurposeEnable) {
+        ASN1_TYPE ext = ASN1_TYPE_EMPTY;
+
+        asn1_create_element(pkix_asn1, "PKIX1.ExtKeyUsageSyntax", &ext);
+        if (req->keyPurposeOID1) {
+            asn1_write_value(ext, "", "NEW", 1);
+            asn1_write_value(ext, "?LAST", req->keyPurposeOID1, 1);
+        }
+        if (req->keyPurposeOID2) {
+            asn1_write_value(ext, "", "NEW", 1);
+            asn1_write_value(ext, "?LAST", req->keyPurposeOID2, 1);
+        }
+        test_tls_der_encode(ext, "", &der);
+        err = gnutls_x509_crt_set_extension_by_oid(
+            crt, "2.5.29.37",
+            der.data, der.size,
+            req->keyPurposeCritical);
+        if (err < 0) {
+            g_critical("Failed to set certificate key purpose %s",
+                       gnutls_strerror(err));
+            g_free(der.data);
+            abort();
+        }
+        asn1_delete_structure(&ext);
+        g_free(der.data);
+    }
+
+    /*
+     * Any old serial number will do, so lets pick 5
+     */
+    err = gnutls_x509_crt_set_serial(crt, serial, 5);
+    if (err < 0) {
+        g_critical("Failed to set certificate serial %s",
+                   gnutls_strerror(err));
+        abort();
+    }
+
+    err = gnutls_x509_crt_set_activation_time(crt, start);
+    if (err < 0) {
+        g_critical("Failed to set certificate activation %s",
+                   gnutls_strerror(err));
+        abort();
+    }
+    err = gnutls_x509_crt_set_expiration_time(crt, expire);
+    if (err < 0) {
+        g_critical("Failed to set certificate expiration %s",
+                   gnutls_strerror(err));
+        abort();
+    }
+
+
+    /*
+     * If no 'ca' is set then we are self signing
+     * the cert. This is done for the root CA certs
+     */
+    err = gnutls_x509_crt_sign(crt, ca ? ca : crt, privkey);
+    if (err < 0) {
+        g_critical("Failed to sign certificate %s",
+                   gnutls_strerror(err));
+        abort();
+    }
+
+    /*
+     * Finally write the new cert out to disk
+     */
+    err = gnutls_x509_crt_export(
+        crt, GNUTLS_X509_FMT_PEM, buffer, &size);
+    if (err < 0) {
+        g_critical("Failed to export certificate %s: %d",
+                   gnutls_strerror(err), err);
+        abort();
+    }
+
+    if (!g_file_set_contents(req->filename, buffer, -1, NULL)) {
+        g_critical("Failed to write certificate %s",
+                   req->filename);
+        abort();
+    }
+
+    req->crt = crt;
+}
+
+
+void test_tls_write_cert_chain(const char *filename,
+                               gnutls_x509_crt_t *certs,
+                               size_t ncerts)
+{
+    size_t i;
+    size_t capacity = 1024, offset = 0;
+    char *buffer = g_new0(char, capacity);
+    int err;
+
+    for (i = 0; i < ncerts; i++) {
+        size_t len = capacity - offset;
+    retry:
+        err = gnutls_x509_crt_export(certs[i], GNUTLS_X509_FMT_PEM,
+                                     buffer + offset, &len);
+        if (err < 0) {
+            if (err == GNUTLS_E_SHORT_MEMORY_BUFFER) {
+                buffer = g_renew(char, buffer, offset + len);
+                capacity = offset + len;
+                goto retry;
+            }
+            g_critical("Failed to export certificate chain %s: %d",
+                       gnutls_strerror(err), err);
+            abort();
+        }
+        offset += len;
+    }
+
+    if (!g_file_set_contents(filename, buffer, offset, NULL)) {
+        abort();
+    }
+}
+
+
+void test_tls_discard_cert(QCryptoTLSTestCertReq *req)
+{
+    if (!req->crt) {
+        return;
+    }
+
+    gnutls_x509_crt_deinit(req->crt);
+    req->crt = NULL;
+
+    if (getenv("QEMU_TEST_DEBUG_CERTS") == NULL) {
+        unlink(req->filename);
+    }
+}
+
+#endif /* QCRYPTO_HAVE_TLS_TEST_SUPPORT */