crypto: deprecate use of external dh-params.pem file

GNUTLS has deprecated use of externally provided diffie-hellman
parameters. Since 3.6.0 it will automatically negotiate DH params
in accordance with RFC7919.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

crypto/tlscreds.c

@@ -22,6 +22,7 @@
 #include "qapi/error.h"
 #include "qapi-types-crypto.h"
 #include "qemu/module.h"
+#include "qemu/error-report.h"
 #include "tlscredspriv.h"
 #include "trace.h"
 
@@ -38,22 +39,7 @@ qcrypto_tls_creds_get_dh_params_file(QCryptoTLSCreds *creds,
 
     trace_qcrypto_tls_creds_load_dh(creds, filename ? filename : "<generated>");
 
-    if (filename == NULL) {
-        ret = gnutls_dh_params_init(dh_params);
-        if (ret < 0) {
-            error_setg(errp, "Unable to initialize DH parameters: %s",
-                       gnutls_strerror(ret));
-            return -1;
-        }
-        ret = gnutls_dh_params_generate2(*dh_params, DH_BITS);
-        if (ret < 0) {
-            gnutls_dh_params_deinit(*dh_params);
-            *dh_params = NULL;
-            error_setg(errp, "Unable to generate DH parameters: %s",
-                       gnutls_strerror(ret));
-            return -1;
-        }
-    } else {
+    if (filename != NULL) {
         GError *gerr = NULL;
         gchar *contents;
         gsize len;
@@ -67,6 +53,10 @@ qcrypto_tls_creds_get_dh_params_file(QCryptoTLSCreds *creds,
             g_error_free(gerr);
             return -1;
         }
+        warn_report_once("Use of an external DH parameters file '%s' is "
+                         "deprecated and will be removed in a future release",
+                         filename);
+
         data.data = (unsigned char *)contents;
         data.size = len;
         ret = gnutls_dh_params_init(dh_params);
@@ -87,6 +77,8 @@ qcrypto_tls_creds_get_dh_params_file(QCryptoTLSCreds *creds,
                        filename, gnutls_strerror(ret));
             return -1;
         }
+    } else {
+        *dh_params = NULL;
     }
 
     return 0;

crypto/tlscredsanon.c

@@ -68,8 +68,10 @@ qcrypto_tls_creds_anon_load(QCryptoTLSCredsAnon *creds,
             return -1;
         }
 
-        gnutls_anon_set_server_dh_params(box->data.anonserver,
-                                         box->dh_params);
+        if (box->dh_params) {
+            gnutls_anon_set_server_dh_params(box->data.anonserver,
+                                             box->dh_params);
+        }
     } else {
         ret = gnutls_anon_allocate_client_credentials(&box->data.anonclient);
         if (ret < 0) {

crypto/tlscredspsk.c

@@ -129,8 +129,10 @@ qcrypto_tls_creds_psk_load(QCryptoTLSCredsPSK *creds,
                        gnutls_strerror(ret));
             goto cleanup;
         }
-        gnutls_psk_set_server_dh_params(box->data.pskserver,
-                                        box->dh_params);
+        if (box->dh_params) {
+            gnutls_psk_set_server_dh_params(box->data.pskserver,
+                                            box->dh_params);
+        }
     } else {
         box = qcrypto_tls_creds_box_new_client(GNUTLS_CRD_PSK);
 

crypto/tlscredsx509.c

@@ -683,7 +683,9 @@ qcrypto_tls_creds_x509_load(QCryptoTLSCredsX509 *creds,
                                                  errp) < 0) {
             return -1;
         }
-        gnutls_certificate_set_dh_params(box->data.cert, box->dh_params);
+        if (box->dh_params) {
+            gnutls_certificate_set_dh_params(box->data.cert, box->dh_params);
+        }
     }
     creds->parent_obj.box = g_steal_pointer(&box);
 

docs/about/deprecated.rst

@@ -385,6 +385,15 @@ Options are:
     - move backing file to NVDIMM storage and keep ``pmem=on``
       (to have NVDIMM with persistence guaranties).
 
+Using an external DH (Diffie-Hellman) parameters file (since 10.2)
+''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
+
+Loading of external Diffie-Hellman parameters from a 'dh-params.pem'
+file is deprecated and will be removed with no replacement in a
+future release. Where no 'dh-params.pem' file is provided, the DH
+parameters will be automatically negotiated in accordance with
+RFC7919.
+
 Device options
 --------------
 

docs/system/tls.rst

@@ -251,11 +251,13 @@ When specifying the object, the ``dir`` parameters specifies which
 directory contains the credential files. This directory is expected to
 contain files with the names mentioned previously, ``ca-cert.pem``,
 ``server-key.pem``, ``server-cert.pem``, ``client-key.pem`` and
-``client-cert.pem`` as appropriate. It is also possible to include a set
-of pre-generated Diffie-Hellman (DH) parameters in a file
-``dh-params.pem``, which can be created using the
-``certtool --generate-dh-params`` command. If omitted, QEMU will
-dynamically generate DH parameters when loading the credentials.
+``client-cert.pem`` as appropriate.
+
+While it is possible to include a set of pre-generated Diffie-Hellman
+(DH) parameters in a file ``dh-params.pem``, this facility is now
+deprecated and will be removed in a future release. When omitted the
+DH parameters will be automatically negotiated in accordance with
+RFC7919.
 
 The ``endpoint`` parameter indicates whether the credentials will be
 used for a network client or server, and determines which PEM files are