[FFmpeg-cvslog] avformat/avidec: Check nb_streams in read_gab2_sub()

[Michael Niedermayer]

ffmpeg | branch: release/3.1 | Michael Niedermayer <michael at niedermayer.cc> | Wed Sep 28 16:14:08 2016 +0200| [622ccbd8ab894e3ac6cdf607e3d4f39e406786e9] | committer: Michael Niedermayer

avformat/avidec: Check nb_streams in read_gab2_sub()

Fixes null pointer dereference
Fixes: 1/null_point.avi

Found-by: 连一汉 <lianyihan at 360.cn>
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit 2679ad4773aa356e7c3da5c68bc81f02a194617f)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=622ccbd8ab894e3ac6cdf607e3d4f39e406786e9
---

 libavformat/avidec.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libavformat/avidec.c b/libavformat/avidec.c
index 410c2d5..3c5f3ec 100644
--- a/libavformat/avidec.c
+++ b/libavformat/avidec.c
@@ -1097,6 +1097,8 @@ static int read_gab2_sub(AVFormatContext *s, AVStream *st, AVPacket *pkt)
             goto error;
 
         if (!avformat_open_input(&ast->sub_ctx, "", sub_demuxer, NULL)) {
+            if (ast->sub_ctx->nb_streams != 1)
+                goto error;
             ff_read_packet(ast->sub_ctx, &ast->sub_pkt);
             avcodec_parameters_copy(st->codecpar, ast->sub_ctx->streams[0]->codecpar);
             time_base = ast->sub_ctx->streams[0]->time_base;