From 6c461e90bc1eedce4b7e414d34c8a8a9162359b5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Wed, 3 Mar 2021 11:31:52 +0200
Subject: [PATCH] matroskademux: Initialize track context out parameter to NULL
 before parsing

Various error return paths don't set it to NULL and callers are only
checking if the pointer is NULL. As it's allocated on the stack this
usually contains random stack memory, and more often than not the memory
of a previously parsed track.

This then causes all kinds of memory corruptions further down the line.

Thanks to Natalie Silvanovich for reporting.

Fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/issues/858

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/902>
---
 gst/matroska/matroska-demux.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/gst/matroska/matroska-demux.c b/gst/matroska/matroska-demux.c
index d7b6f7edc..e878e0d66 100644
--- a/gst/matroska/matroska-demux.c
+++ b/gst/matroska/matroska-demux.c
@@ -694,6 +694,8 @@ gst_matroska_demux_parse_stream (GstMatroskaDemux * demux, GstEbmlRead * ebml,
 
   DEBUG_ELEMENT_START (demux, ebml, "TrackEntry");
 
+  *dest_context = NULL;
+
   /* start with the master */
   if ((ret = gst_ebml_read_master (ebml, &id)) != GST_FLOW_OK) {
     DEBUG_ELEMENT_STOP (demux, ebml, "TrackEntry", ret);
-- 
GitLab
