avformat/mpc8: fix hang with fuzzed file

This can lead to an endless loop by seeking back a few bytes after each
attempted chunk read. Assuming negative sizes are always invalid, this
is easy to fix. Other code in this demuxer treats negative sizes as
invalid as well.

Fixes ticket #4262.

Signed-off-by: Michael Niedermayer <[email protected]>
(cherry picked from commit 56cc024220886927350cfc26ee695062ca7ecaf4)

Signed-off-by: Michael Niedermayer <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/libavformat/mpc8.c b/libavformat/mpc8.c
index db23781613..161cee3367 100644
--- a/libavformat/mpc8.c
+++ b/libavformat/mpc8.c
@@ -204,6 +204,10 @@ static int mpc8_read_header(AVFormatContext *s, AVFormatParameters *ap)
     while(!url_feof(pb)){
         pos = avio_tell(pb);
         mpc8_get_chunk_header(pb, &tag, &size);
+        if (size < 0) {
+            av_log(s, AV_LOG_ERROR, "Invalid chunk length\n");
+            return AVERROR_INVALIDDATA;
+        }
         if(tag == TAG_STREAMHDR)
             break;
         mpc8_handle_chunk(s, tag, pos, size);