qcow2: don't permit changing encryption parameters

Currently if trying to change encryption parameters on a qcow2 image, qemu-img
will abort. We already explicitly check for attempt to change encrypt.format
but missed other parameters like encrypt.key-secret. Rather than list each
parameter, just blacklist changing of all parameters with a 'encrypt.' prefix.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/qcow2.c

@@ -4069,6 +4069,9 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
                 error_report("Changing the encryption format is not supported");
                 return -ENOTSUP;
             }
+        } else if (g_str_has_prefix(desc->name, "encrypt.")) {
+            error_report("Changing the encryption parameters is not supported");
+            return -ENOTSUP;
         } else if (!strcmp(desc->name, BLOCK_OPT_CLUSTER_SIZE)) {
             cluster_size = qemu_opt_get_size(opts, BLOCK_OPT_CLUSTER_SIZE,
                                              cluster_size);