migration: add support for a "tls-authz" migration parameter

The QEMU instance that runs as the server for the migration data
transport (ie the target QEMU) needs to be able to configure access
control so it can prevent unauthorized clients initiating an incoming
migration. This adds a new 'tls-authz' migration parameter that is used
to provide the QOM ID of a QAuthZ subclass instance that provides the
access control check. This is checked against the x509 certificate
obtained during the TLS handshake.

For example, when starting a QEMU for incoming migration, it is
possible to give an example identity of the source QEMU that is
intended to be connecting later:

  $QEMU \
     -monitor stdio \
     -incoming defer \
     ...other args...

  (qemu) object_add tls-creds-x509,id=tls0,dir=/home/berrange/qemutls,\
             endpoint=server,verify-peer=yes \
  (qemu) object_add authz-simple,id=auth0,identity=CN=laptop.example.com,,\
             O=Example Org,,L=London,,ST=London,,C=GB \
  (qemu) migrate_incoming tcp:localhost:9000

Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

hmp.c

@@ -441,6 +441,9 @@ void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict)
         monitor_printf(mon, "%s: %" PRIu64 "\n",
             MigrationParameter_str(MIGRATION_PARAMETER_MAX_POSTCOPY_BANDWIDTH),
             params->max_postcopy_bandwidth);
+        monitor_printf(mon, " %s: '%s'\n",
+            MigrationParameter_str(MIGRATION_PARAMETER_TLS_AUTHZ),
+            params->has_tls_authz ? params->tls_authz : "");
     }
 
     qapi_free_MigrationParameters(params);
@@ -1783,6 +1786,12 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
         p->tls_hostname->type = QTYPE_QSTRING;
         visit_type_str(v, param, &p->tls_hostname->u.s, &err);
         break;
+    case MIGRATION_PARAMETER_TLS_AUTHZ:
+        p->has_tls_authz = true;
+        p->tls_authz = g_new0(StrOrNull, 1);
+        p->tls_authz->type = QTYPE_QSTRING;
+        visit_type_str(v, param, &p->tls_authz->u.s, &err);
+        break;
     case MIGRATION_PARAMETER_MAX_BANDWIDTH:
         p->has_max_bandwidth = true;
         /*

migration/migration.c

@@ -757,6 +757,8 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
     params->tls_creds = g_strdup(s->parameters.tls_creds);
     params->has_tls_hostname = true;
     params->tls_hostname = g_strdup(s->parameters.tls_hostname);
+    params->has_tls_authz = true;
+    params->tls_authz = g_strdup(s->parameters.tls_authz);
     params->has_max_bandwidth = true;
     params->max_bandwidth = s->parameters.max_bandwidth;
     params->has_downtime_limit = true;
@@ -1331,6 +1333,12 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
         s->parameters.tls_hostname = g_strdup(params->tls_hostname->u.s);
     }
 
+    if (params->has_tls_authz) {
+        g_free(s->parameters.tls_authz);
+        assert(params->tls_authz->type == QTYPE_QSTRING);
+        s->parameters.tls_authz = g_strdup(params->tls_authz->u.s);
+    }
+
     if (params->has_max_bandwidth) {
         s->parameters.max_bandwidth = params->max_bandwidth;
         if (s->to_dst_file) {

migration/tls.c

@@ -94,7 +94,7 @@ void migration_tls_channel_process_incoming(MigrationState *s,
 
     tioc = qio_channel_tls_new_server(
         ioc, creds,
-        NULL, /* XXX pass ACL name */
+        s->parameters.tls_authz,
         errp);
     if (!tioc) {
         return;

qapi/migration.json

@@ -541,6 +541,12 @@
 #                hostname must be provided so that the server's x509
 #                certificate identity can be validated. (Since 2.7)
 #
+# @tls-authz: ID of the 'authz' object subclass that provides access control
+#             checking of the TLS x509 certificate distinguished name.
+#             This object is only resolved at time of use, so can be deleted
+#             and recreated on the fly while the migration server is active.
+#             If missing, it will default to denying access (Since 4.0)
+#
 # @max-bandwidth: to set maximum speed for migration. maximum speed in
 #                 bytes per second. (Since 2.8)
 #
@@ -582,7 +588,7 @@
            'compress-level', 'compress-threads', 'decompress-threads',
            'compress-wait-thread',
            'cpu-throttle-initial', 'cpu-throttle-increment',
-           'tls-creds', 'tls-hostname', 'max-bandwidth',
+           'tls-creds', 'tls-hostname', 'tls-authz', 'max-bandwidth',
            'downtime-limit', 'x-checkpoint-delay', 'block-incremental',
            'multifd-channels',
            'xbzrle-cache-size', 'max-postcopy-bandwidth',
@@ -693,6 +699,7 @@
             '*cpu-throttle-increment': 'int',
             '*tls-creds': 'StrOrNull',
             '*tls-hostname': 'StrOrNull',
+            '*tls-authz': 'StrOrNull',
             '*max-bandwidth': 'int',
             '*downtime-limit': 'int',
             '*x-checkpoint-delay': 'int',
@@ -773,6 +780,10 @@
 #                associated with the migration URI, if any. (Since 2.9)
 #                Note: 2.8 reports this by omitting tls-hostname instead.
 #
+# @tls-authz: ID of the 'authz' object subclass that provides access control
+#             checking of the TLS x509 certificate distinguished name. (Since
+#             4.0)
+#
 # @max-bandwidth: to set maximum speed for migration. maximum speed in
 #                 bytes per second. (Since 2.8)
 #
@@ -821,6 +832,7 @@
             '*cpu-throttle-increment': 'uint8',
             '*tls-creds': 'str',
             '*tls-hostname': 'str',
+            '*tls-authz': 'str',
             '*max-bandwidth': 'size',
             '*downtime-limit': 'uint64',
             '*x-checkpoint-delay': 'uint32',