avcodec/cdgraphics: Check frame before clearing

Fixes: null pointer dereference
Fixes: 27730/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_CDGRAPHICS_fuzzer-6212402236096512
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Anton Khirnov <anton@khirnov.net>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

diff --git a/libavcodec/cdgraphics.c b/libavcodec/cdgraphics.c
index 965f43684ad8e6c27e11633d3b72592ecc44d566..263459d0f2e1d98f99c1a7b2a487fde8897e237c 100644 (file)
--- a/libavcodec/cdgraphics.c
+++ b/libavcodec/cdgraphics.c
@@ -369,6 +369,9 @@ static void cdg_decode_flush(AVCodecContext *avctx)
 {
     CDGraphicsContext *cc = avctx->priv_data;
 
+    if (!cc->frame->data[0])
+        return;
+
     memset(cc->frame->data[0], 0, cc->frame->linesize[0] * avctx->height);
     if (!avctx->frame_number)
         memset(cc->frame->data[1], 0, AVPALETTE_SIZE);