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

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

---
 crypto/tlscreds.c         | 24 ++++++++----------------
 crypto/tlscredsanon.c     |  6 ++++--
 crypto/tlscredspsk.c      |  6 ++++--
 crypto/tlscredsx509.c     |  4 +++-
 docs/about/deprecated.rst |  9 +++++++++
 docs/system/tls.rst       | 12 +++++++-----
 6 files changed, 35 insertions(+), 26 deletions(-)

diff --git a/crypto/tlscreds.c b/crypto/tlscreds.c
index 798c9712fb..85268f3b57 100644
--- a/crypto/tlscreds.c
+++ b/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;
diff --git a/crypto/tlscredsanon.c b/crypto/tlscredsanon.c
index 69ed1d792a..777cc4f5bb 100644
--- a/crypto/tlscredsanon.c
+++ b/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) {
diff --git a/crypto/tlscredspsk.c b/crypto/tlscredspsk.c
index e437985260..801da50625 100644
--- a/crypto/tlscredspsk.c
+++ b/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);

diff --git a/crypto/tlscredsx509.c b/crypto/tlscredsx509.c
index 2fc0872627..7e79af4266 100644
--- a/crypto/tlscredsx509.c
+++ b/crypto/tlscredsx509.c
@@ -684,7 +684,9 @@ 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);

diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
index ca6b3769b5..694a69da64 100644
--- a/docs/about/deprecated.rst
+++ b/docs/about/deprecated.rst
@@ -365,6 +365,15 @@ 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
 --------------

diff --git a/docs/system/tls.rst b/docs/system/tls.rst
index a4f6781d62..44c4bf04e9 100644
--- a/docs/system/tls.rst
+++ b/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
--
2.51.1