From 5e54a871c5e38225a3575c92196b1355f7744f1b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kacper=20Michaj=C5=82ow?= <kasper93@gmail.com>
Date: Sun, 28 Jan 2024 04:19:36 +0100
Subject: [PATCH] demux_mkv: error if needed compression settings were not
 found

Mode 3 is header stripping and we need ContentCompSettings to
reconstruct the data.

Found by fuzzing.
---
 demux/demux_mkv.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/demux/demux_mkv.c b/demux/demux_mkv.c
index 3b37c863ac..50f4c78b25 100644
--- a/demux/demux_mkv.c
+++ b/demux/demux_mkv.c
@@ -390,6 +390,10 @@ static bstr demux_mkv_decode(struct mp_log *log, mkv_track_t *track,
             }
             size = dstlen - out_avail;
         } else if (enc->comp_algo == 3) {
+            if (enc->comp_settings_len == 0 || !enc->comp_settings) {
+                mp_warn(log, "missing comp_settings, unable to reconstruct the data.\n");
+                goto error;
+            }
             dest = talloc_size(track->parser_tmp, size + enc->comp_settings_len);
             memcpy(dest, enc->comp_settings, enc->comp_settings_len);
             memcpy(dest + enc->comp_settings_len, src, size);