[FFmpeg-cvslog] avformat/mpc8: fix hang with fuzzed file

[wm4]

ffmpeg | branch: master | wm4 <nfxjfg at googlemail.com> | Tue Feb  3 19:04:12 2015 +0100| [56cc024220886927350cfc26ee695062ca7ecaf4] | committer: Michael Niedermayer

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 <michaelni at gmx.at>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=56cc024220886927350cfc26ee695062ca7ecaf4
---

 libavformat/mpc8.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/libavformat/mpc8.c b/libavformat/mpc8.c
index a15dc25..722d0ee 100644
--- a/libavformat/mpc8.c
+++ b/libavformat/mpc8.c
@@ -223,6 +223,10 @@ static int mpc8_read_header(AVFormatContext *s)
     while(!avio_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);