[FFmpeg-cvslog] avcodec/shorten: Sanity check nmeans

[Michael Niedermayer]

ffmpeg | branch: release/4.0 | Michael Niedermayer <michael at niedermayer.cc> | Tue Jun  5 13:03:48 2018 +0200| [3aa3b05d64040e4be8e840a969add39ffb72c54a] | committer: Michael Niedermayer

avcodec/shorten: Sanity check nmeans

Fixes: OOM
Fixes: 8195/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SHORTEN_fuzzer-5179785826271232

The reference software appears to use longs for 32bits and it uses int for nmeans
hinting that the intended maximum size was not 32bit.

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit d91a0b503d7a886587281bc1ee42476aa5e89f85)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=3aa3b05d64040e4be8e840a969add39ffb72c54a
---

 libavcodec/shorten.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/libavcodec/shorten.c b/libavcodec/shorten.c
index ae0cdfe09d..8aeacfeb31 100644
--- a/libavcodec/shorten.c
+++ b/libavcodec/shorten.c
@@ -450,6 +450,10 @@ static int read_header(ShortenContext *s)
             return AVERROR_INVALIDDATA;
         }
         s->nmean = get_uint(s, 0);
+        if (s->nmean > 32768U) {
+            av_log(s->avctx, AV_LOG_ERROR, "nmean is: %d\n", s->nmean);
+            return AVERROR_INVALIDDATA;
+        }
 
         skip_bytes = get_uint(s, NSKIPSIZE);
         if ((unsigned)skip_bytes > get_bits_left(&s->gb)/8) {