wavpack: check that there aren't too many blocks per packet

libavcodec/wavpack.c

@@ -1120,6 +1120,11 @@ static int wavpack_decode_block(AVCodecContext *avctx, int block_no,
         }
     }
 
+    if (wc->ch_offset + s->stereo >= avctx->channels) {
+        av_log(avctx, AV_LOG_WARNING, "Too many channels coded in a packet.\n");
+        return (avctx->err_recognition & AV_EF_EXPLODE) ? AVERROR_INVALIDDATA : 0;
+    }
+
     samples_l = frame->extended_data[wc->ch_offset];
     if (s->stereo)
         samples_r = frame->extended_data[wc->ch_offset + 1];