[FFmpeg-cvslog] avcodec/pdvdec: Check previous frame before using it

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Tue May  2 01:55:34 2023 +0200| [5cc378cc466121fc9de1657ea76deeba9f92089a] | committer: Michael Niedermayer

avcodec/pdvdec: Check previous frame before using it

Fixes: load of null pointer of type 'uint8_t' (aka 'unsigned char')
Fixes: 58256/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PDV_fuzzer-4776436325285888

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Paul B Mahol <onemda at gmail.com>
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=5cc378cc466121fc9de1657ea76deeba9f92089a
---

 libavcodec/pdvdec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/pdvdec.c b/libavcodec/pdvdec.c
index 3ac2f98b3d..d50c4e729c 100644
--- a/libavcodec/pdvdec.c
+++ b/libavcodec/pdvdec.c
@@ -93,7 +93,7 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *frame,
             return AVERROR_INVALIDDATA;
         }
 
-        if (!(avpkt->flags & AV_PKT_FLAG_KEY)) {
+        if (prev && !(avpkt->flags & AV_PKT_FLAG_KEY)) {
             for (int j = 0; j < (avctx->width + 7) >> 3; j++)
                 dst[j] ^= prev[j];
             prev += prev_frame->linesize[0];