From 3f62e9fbd3de11df52184ca8dfcabfb7d1c0fdeb Mon Sep 17 00:00:00 2001
From: Robert Tiemann <rtie@gmx.de>
Date: Fri, 17 May 2019 12:43:04 +0200
Subject: [PATCH] Avoid possible crash when getting server properties.

The crash occurs when calling dls_device_get_all_props() for a content
directory server that we have not yet subscribed to (that is,
prv_cds_subscribed() returns FALSE in
prv_get_system_update_id_for_props()). This crash is caused by an
invalid GVariantBuilder passed to g_variant_builder_end() in
prv_get_sleeping_for_props(), leading to a NULL result pointer being
passed to dls_async_task_complete(). A GVariant is attempted to be
constructed from this NULL pointer in dls_task_complete().

Here is the call chain that leads to the crash:

    dls_device_get_all_props()
    prv_get_system_update_id_for_props()
    gupnp_service_proxy_begin_action("GetSystemUpdateID") -> prv_system_update_id_for_props_cb()
    prv_system_update_id_for_props_cb()
    prv_get_sr_token_for_props()
    prv_get_sleeping_for_props()
    dls_async_task_complete()
    cb_data->cb() -> prv_async_task_complete()
    prv_async_task_complete()
    dls_task_complete()
    g_variant_new()

The crash was most likely observed when a device running Plex Media
Server was present on the network.

This commit moves the call of g_variant_builder_end() in
prv_system_update_id_for_props_cb() (which invalidates the
GVariantBuilder used later in prv_get_sleeping_for_props()) to the
error handling branch. This leaves the GVariantBuilder alone and
allows prv_get_sr_token_for_props() or one of its descendants to call
g_variant_builder_end() and complete the task.
---
 libdleyna/server/device.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/libdleyna/server/device.c b/libdleyna/server/device.c
index d77dfbc2725b..8777da0ea2db 100644
--- a/libdleyna/server/device.c
+++ b/libdleyna/server/device.c
@@ -2256,15 +2256,14 @@ static void prv_system_update_id_for_props_cb(GUPnPServiceProxy *proxy,
 			      DLS_SYSTEM_UPDATE_VAR,
 			      g_variant_new_uint32(id));
 
-	cb_data->task.result = g_variant_ref_sink(g_variant_builder_end(
-							cb_task_data->vb));
-
 on_complete:
 
 	if (!cb_data->error)
 		prv_get_sr_token_for_props(proxy, cb_data->task.target.device,
 					   cb_data);
 	else {
+		cb_data->task.result = g_variant_ref_sink(g_variant_builder_end(
+							cb_task_data->vb));
 		(void) g_idle_add(dls_async_task_complete, cb_data);
 		g_cancellable_disconnect(cb_data->cancellable,
 					 cb_data->cancel_id);
-- 
2.28.0