monitor: Fix tracepoint crash on JSON syntax error

When tracepoint handle_qmp_command is enabled, we crash on JSON syntax
errors.  Broken in commit 1cc37471525.  Fix by skipping the tracepoint
on JSON syntax error.  Before the flawed commit, we skipped it by
returning early.

Fixes: CID 1394216
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20180716091012.29510-1-armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>

diff --git a/monitor.c b/monitor.c
index 7af1f18..be29634 100644 (file)
--- a/monitor.c
+++ b/monitor.c
@@ -4224,7 +4224,7 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
         qdict_del(qdict, "id");
     } /* else will fail qmp_dispatch() */
 
-    if (trace_event_get_state_backends(TRACE_HANDLE_QMP_COMMAND)) {
+    if (req && trace_event_get_state_backends(TRACE_HANDLE_QMP_COMMAND)) {
         QString *req_json = qobject_to_json(req);
         trace_handle_qmp_command(mon, qstring_get_str(req_json));
         qobject_unref(req_json);