[FFmpeg-cvslog] smvjpegdec: make sure cur_frame is not negative

[Andreas Cadhalpun]

ffmpeg | branch: release/2.8 | Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com> | Thu Nov 10 22:09:03 2016 +0100| [f76947fd567f20287bc8ca8e692a59026bac19e7] | committer: Andreas Cadhalpun

smvjpegdec: make sure cur_frame is not negative

This fixes a heap-buffer-overflow detected by AddressSanitizer.

Reviewed-by: Michael Niedermayer <michael at niedermayer.cc>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
(cherry picked from commit 360bc0d90aa66cf21e9f488e77d21db18e01ec9c)
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=f76947fd567f20287bc8ca8e692a59026bac19e7
---

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

diff --git a/libavcodec/smvjpegdec.c b/libavcodec/smvjpegdec.c
index 9c2fb38..2235ed5 100644
--- a/libavcodec/smvjpegdec.c
+++ b/libavcodec/smvjpegdec.c
@@ -152,6 +152,10 @@ static int smvjpeg_decode_frame(AVCodecContext *avctx, void *data, int *data_siz
 
     cur_frame = avpkt->pts % s->frames_per_jpeg;
 
+    /* cur_frame is later used to calculate the buffer offset, so it mustn't be negative */
+    if (cur_frame < 0)
+        cur_frame += s->frames_per_jpeg;
+
     /* Are we at the start of a block? */
     if (!cur_frame) {
         av_frame_unref(mjpeg_data);