[Qemu-devel] [PATCH v3 2/7] crypto: introduce new module for TLS anonymous credentials

[Daniel P. Berrange]

Introduce a QCryptoTLSCredsAnon class which is used to
manage anonymous TLS credentials. Use of this class is
generally discouraged since it does not offer strong
security, but it is required for backwards compatibility
with the current VNC server implementation.

Simple example CLI configuration:

 $QEMU -object tls-creds-anon,id=tls0,endpoint=server

Example using pre-created diffie-hellman parameters

 $QEMU -object tls-creds-anon,id=tls0,endpoint=server,\
               dir=/path/to/creds/dir

The 'id' value in the -object args will be used to associate the
credentials with the network services. For eample, when the VNC
server is later converted it would use

 $QEMU -object tls-creds-anon,id=tls0,.... \
       -vnc 127.0.0.1:1,tls-creds=tls0

Signed-off-by: Daniel P. Berrange <address@hidden>
---
 crypto/Makefile.objs          |   1 +
 crypto/init.c                 |   8 ++
 crypto/tlscredsanon.c         | 235 ++++++++++++++++++++++++++++++++++++++++++
 include/crypto/tlscredsanon.h | 113 ++++++++++++++++++++
 qemu-options.hx               |  20 ++++
 5 files changed, 377 insertions(+)
 create mode 100644 crypto/tlscredsanon.c
 create mode 100644 include/crypto/tlscredsanon.h

diff --git a/crypto/Makefile.objs b/crypto/Makefile.objs
index cf62d51..cf0199e 100644
--- a/crypto/Makefile.objs
+++ b/crypto/Makefile.objs
@@ -4,3 +4,4 @@ util-obj-y += aes.o
 util-obj-y += desrfb.o
 util-obj-y += cipher.o
 util-obj-y += tlscreds.o
+util-obj-y += tlscredsanon.o
diff --git a/crypto/init.c b/crypto/init.c
index 7447882..bc4d769 100644
--- a/crypto/init.c
+++ b/crypto/init.c
@@ -19,6 +19,7 @@
  */
 
 #include "crypto/init.h"
+#include "crypto/tlscredsanon.h"
 #include "qemu/thread.h"
 
 #ifdef CONFIG_GNUTLS
@@ -137,6 +138,13 @@ int qcrypto_init(Error **errp)
     gcry_control(GCRYCTL_INITIALIZATION_FINISHED, 0);
 #endif
 
+    /* XXX hack - if we don't reference any function in tlscreds*.c
+     * then the linker drops tlscred*.o from libqemutil.a when it
+     * links the emulators as it thinks it is unused. It isn't
+     * clever enough to see the constructor :-(
+     */
+    qcrypto_tls_creds_anon_dummy();
+
     return 0;
 }
 
diff --git a/crypto/tlscredsanon.c b/crypto/tlscredsanon.c
new file mode 100644
index 0000000..b51ea90
--- /dev/null
+++ b/crypto/tlscredsanon.c
@@ -0,0 +1,235 @@
+/*
+ * QEMU crypto TLS anonymous 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/tlscredsanon.h"
+#include "crypto/tlscredspriv.h"
+#include "qom/object_interfaces.h"
+
+/* #define QCRYPTO_DEBUG */
+
+#ifdef QCRYPTO_DEBUG
+#define DPRINTF(fmt, ...) do { fprintf(stderr, fmt, ## __VA_ARGS__); } while 
(0)
+#else
+#define DPRINTF(fmt, ...) do { } while (0)
+#endif
+
+
+#ifdef CONFIG_GNUTLS
+
+
+static int
+qcrypto_tls_creds_anon_load(QCryptoTLSCredsAnon *creds,
+                            Error **errp)
+{
+    char *dhparams = NULL;
+    int ret;
+    int rv = -1;
+
+    DPRINTF("Loading anon creds %d from %s\n",
+            creds->type, creds->dir ? creds->dir : "<nodir>");
+
+    if (creds->parent_obj.endpoint == QCRYPTO_TLS_CREDS_ENDPOINT_SERVER) {
+        if (qcrypto_tls_creds_get_path(&creds->parent_obj,
+                                       QCRYPTO_TLS_CREDS_DH_PARAMS,
+                                       false, &dhparams, errp) < 0) {
+            goto cleanup;
+        }
+
+        ret = gnutls_anon_allocate_server_credentials(&creds->data.server);
+        if (ret < 0) {
+            error_setg(errp, "Cannot allocate credentials: %s",
+                       gnutls_strerror(ret));
+            goto cleanup;
+        }
+
+        if (qcrypto_tls_creds_get_dh_params_file(dhparams,
+                                                 &creds->parent_obj.dh_params,
+                                                 errp) < 0) {
+            goto cleanup;
+        }
+
+        gnutls_anon_set_server_dh_params(creds->data.server,
+                                         creds->parent_obj.dh_params);
+    } else {
+        ret = gnutls_anon_allocate_client_credentials(&creds->data.client);
+        if (ret < 0) {
+            error_setg(errp, "Cannot allocate credentials: %s",
+                       gnutls_strerror(ret));
+            goto cleanup;
+        }
+    }
+
+    rv = 0;
+ cleanup:
+    g_free(dhparams);
+    return rv;
+}
+
+
+static void
+qcrypto_tls_creds_anon_unload(QCryptoTLSCredsAnon *creds)
+{
+    if (creds->parent_obj.endpoint == QCRYPTO_TLS_CREDS_ENDPOINT_CLIENT) {
+        if (creds->data.client) {
+            gnutls_anon_free_client_credentials(creds->data.client);
+            creds->data.client = NULL;
+        }
+    } else {
+        if (creds->data.server) {
+            gnutls_anon_free_server_credentials(creds->data.server);
+            creds->data.server = NULL;
+        }
+    }
+    if (creds->parent_obj.dh_params) {
+        gnutls_dh_params_deinit(creds->parent_obj.dh_params);
+        creds->parent_obj.dh_params = NULL;
+    }
+}
+
+#else /* ! CONFIG_GNUTLS */
+
+
+static void
+qcrypto_tls_creds_anon_load(QCryptoTLSCredsAnon *creds G_GNUC_UNUSED,
+                            Error **errp)
+{
+    error_setg(errp, "TLS credentials support requires GNUTLS");
+}
+
+
+static void
+qcrypto_tls_creds_anon_unload(QCryptoTLSCredsAnon *creds G_GNUC_UNUSED)
+{
+    /* nada */
+}
+
+
+#endif /* ! CONFIG_GNUTLS */
+
+
+static void
+qcrypto_tls_creds_anon_prop_set_loaded(Object *obj,
+                                       bool value,
+                                       Error **errp)
+{
+    QCryptoTLSCredsAnon *creds = QCRYPTO_TLS_CREDS_ANON(obj);
+
+    if (value) {
+        qcrypto_tls_creds_anon_load(creds, errp);
+    } else {
+        qcrypto_tls_creds_anon_unload(creds);
+    }
+}
+
+
+#ifdef CONFIG_GNUTLS
+
+
+static bool
+qcrypto_tls_creds_anon_prop_get_loaded(Object *obj,
+                                       Error **errp G_GNUC_UNUSED)
+{
+    QCryptoTLSCredsAnon *creds = QCRYPTO_TLS_CREDS_ANON(obj);
+
+    if (creds->parent_obj.endpoint == QCRYPTO_TLS_CREDS_ENDPOINT_SERVER) {
+        return creds->data.server != NULL;
+    } else {
+        return creds->data.client != NULL;
+    }
+}
+
+
+#else /* ! CONFIG_GNUTLS */
+
+
+static bool
+qcrypto_tls_creds_anon_prop_get_loaded(Object *obj G_GNUC_UNUSED,
+                                       Error **errp G_GNUC_UNUSED)
+{
+    return false;
+}
+
+
+#endif /* ! CONFIG_GNUTLS */
+
+
+static void
+qcrypto_tls_creds_anon_complete(UserCreatable *uc, Error **errp)
+{
+    object_property_set_bool(OBJECT(uc), true, "loaded", errp);
+}
+
+
+static void
+qcrypto_tls_creds_anon_init(Object *obj)
+{
+    object_property_add_bool(obj, "loaded",
+                             qcrypto_tls_creds_anon_prop_get_loaded,
+                             qcrypto_tls_creds_anon_prop_set_loaded,
+                             NULL);
+}
+
+
+static void
+qcrypto_tls_creds_anon_finalize(Object *obj)
+{
+    QCryptoTLSCredsAnon *creds = QCRYPTO_TLS_CREDS_ANON(obj);
+
+    qcrypto_tls_creds_anon_unload(creds);
+}
+
+
+static void
+qcrypto_tls_creds_anon_class_init(ObjectClass *oc, void *data)
+{
+    UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
+
+    ucc->complete = qcrypto_tls_creds_anon_complete;
+}
+
+
+static const TypeInfo qcrypto_tls_creds_anon_info = {
+    .parent = TYPE_QCRYPTO_TLS_CREDS,
+    .name = TYPE_QCRYPTO_TLS_CREDS_ANON,
+    .instance_size = sizeof(QCryptoTLSCredsAnon),
+    .instance_init = qcrypto_tls_creds_anon_init,
+    .instance_finalize = qcrypto_tls_creds_anon_finalize,
+    .class_size = sizeof(QCryptoTLSCredsAnonClass),
+    .class_init = qcrypto_tls_creds_anon_class_init,
+    .interfaces = (InterfaceInfo[]) {
+        { TYPE_USER_CREATABLE },
+        { }
+    }
+};
+
+
+static void
+qcrypto_tls_creds_anon_register_types(void)
+{
+    DPRINTF("Register TLS anon\n");
+    type_register_static(&qcrypto_tls_creds_anon_info);
+}
+
+void
+qcrypto_tls_creds_anon_dummy(void)
+{
+}
+
+type_init(qcrypto_tls_creds_anon_register_types);
diff --git a/include/crypto/tlscredsanon.h b/include/crypto/tlscredsanon.h
new file mode 100644
index 0000000..6eeffed
--- /dev/null
+++ b/include/crypto/tlscredsanon.h
@@ -0,0 +1,113 @@
+/*
+ * QEMU crypto TLS anonymous 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/>.
+ *
+ */
+
+#ifndef QCRYPTO_TLSCRED_ANON_H__
+#define QCRYPTO_TLSCRED_ANON_H__
+
+#include "crypto/tlscreds.h"
+
+#define TYPE_QCRYPTO_TLS_CREDS_ANON "tls-creds-anon"
+#define QCRYPTO_TLS_CREDS_ANON(obj)                  \
+    OBJECT_CHECK(QCryptoTLSCredsAnon, (obj), TYPE_QCRYPTO_TLS_CREDS_ANON)
+
+
+typedef struct QCryptoTLSCredsAnon QCryptoTLSCredsAnon;
+typedef struct QCryptoTLSCredsAnonClass QCryptoTLSCredsAnonClass;
+
+/**
+ * QCryptoTLSCredsAnon:
+ *
+ * The QCryptoTLSCredsAnon object provides a representation
+ * of anonymous credentials used perform a TLS handshake.
+ * This is primarily provided for backwards compatibility and
+ * its use is discouraged as it has poor security characteristics
+ * due to lacking MITM attack protection amongst other problems.
+ *
+ * This is a user creatable object, which can be instantiated
+ * via object_new_propv():
+ *
+ * <example>
+ *   <title>Creating anonymous TLS credential objects in code</title>
+ *   <programlisting>
+ *   Object *obj;
+ *   Error *err = NULL;
+ *   obj = object_new_propv(TYPE_QCRYPTO_TLS_CREDS_ANON,
+ *                          "tlscreds0",
+ *                          &err,
+ *                          "endpoint", "server",
+ *                          "dir", "/path/x509/cert/dir",
+ *                          "verify-peer", "yes",
+ *                          NULL);
+ *   </programlisting>
+ * </example>
+ *
+ * Or via QMP:
+ *
+ * <example>
+ *   <title>Creating anonymous TLS credential objects via QMP</title>
+ *   <programlisting>
+ *    {
+ *       "execute": "object-add", "arguments": {
+ *          "id": "tlscreds0",
+ *          "qom-type": "tls-creds-anon",
+ *          "props": {
+ *             "endpoint": "server",
+ *             "dir": "/path/to/x509/cert/dir",
+ *             "verify-peer": false
+ *          }
+ *       }
+ *    }
+ *   </programlisting>
+ * </example>
+ *
+ *
+ * Or via the CLI:
+ *
+ * <example>
+ *   <title>Creating anonymous TLS credential objects via CLI</title>
+ *   <programlisting>
+ *  qemu-system-x86_64 -object tls-creds-anon,id=tlscreds0,\
+ *          endpoint=server,verify-peer=off,\
+ *          dir=/path/to/x509/certdir/
+ *   </programlisting>
+ * </example>
+ *
+ */
+
+
+struct QCryptoTLSCredsAnon {
+    QCryptoTLSCreds parent_obj;
+#ifdef CONFIG_GNUTLS
+    union {
+        gnutls_anon_server_credentials_t server;
+        gnutls_anon_client_credentials_t client;
+    } data;
+#endif
+};
+
+
+struct QCryptoTLSCredsAnonClass {
+    QCryptoTLSCredsClass parent_class;
+};
+
+void qcrypto_tls_creds_anon_dummy(void);
+
+#endif /* QCRYPTO_TLSCRED_H__ */
+
diff --git a/qemu-options.hx b/qemu-options.hx
index 77f5853..057801a 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3568,6 +3568,26 @@ the @option{virtio-rng} device. The @option{chardev} 
parameter is
 the unique ID of a character device backend that provides the connection
 to the RNG daemon.
 
address@hidden -object 
tls-creds-anon,address@hidden,address@hidden,address@hidden/path/to/cred/dir},address@hidden|off}
+
+Creates a TLS anonymous credentials object, which can be used to provide
+TLS support on network backends. The @option{id} parameter is a unique
+ID which network backends will use to access the credentials. The
address@hidden is either @option{server} or @option{client} depending
+on whether the QEMU network backend that uses the credentials will be
+acting as a client or as a server. If @option{verify-peer} is enabled
+(the default) then once the handshake is completed, the peer credentials
+will be verified, though this is a no-op for anonymous credentials.
+
+The @var{dir} parameter tells QEMU where to find the credential
+files. For server endpoints, this directory may contain a file
address@hidden providing diffie-hellman parameters to use
+for the TLS server. If the file is missing, QEMU will generate
+a set of DH parameters at startup. This is a computationally
+expensive operation that consumes random pool entropy, so it is
+recommended that a persistent set of parameters be generated
+upfront and saved.
+
 @end table
 
 ETEXI
-- 
2.4.3