From ae08eec6a1f2129cd231a0ab664f0f17b854d138 Mon Sep 17 00:00:00 2001
From: Anton Khirnov <anton@khirnov.net>
Date: Fri, 2 Apr 2021 16:00:23 +0200
Subject: [PATCH] lavc/pngdec: improve chunk length check

The length does not cover the chunk type or CRC.
---
 libavcodec/pngdec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index f3295688c69..0ff81d740c1 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -1217,7 +1217,7 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
         }
 
         length = bytestream2_get_be32(&s->gb);
-        if (length > 0x7fffffff || length > bytestream2_get_bytes_left(&s->gb)) {
+        if (length > 0x7fffffff || length + 8 > bytestream2_get_bytes_left(&s->gb)) {
             av_log(avctx, AV_LOG_ERROR, "chunk too big\n");
             ret = AVERROR_INVALIDDATA;
             goto fail;
-- 
2.39.2