[FFmpeg-cvslog] lavc/pngdec: improve chunk length check

[Anton Khirnov]

ffmpeg | branch: release/4.4 | Anton Khirnov <anton at khirnov.net> | Fri Apr  2 16:00:23 2021 +0200| [c64180fac8442d4b0f1ed9cb07265361c193400e] | committer: Anton Khirnov

lavc/pngdec: improve chunk length check

The length does not cover the chunk type or CRC.

(cherry picked from commit ae08eec6a1f2129cd231a0ab664f0f17b854d138)
Signed-off-by: Anton Khirnov <anton at khirnov.net>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=c64180fac8442d4b0f1ed9cb07265361c193400e
---

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

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index f3295688c6..0ff81d740c 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;