From 65b1ba680fb67902a9c876a49d0146eaae5a1c3d Mon Sep 17 00:00:00 2001
From: Michael Niedermayer <michael@niedermayer.cc>
Date: Thu, 25 Jun 2020 19:22:01 +0200
Subject: [PATCH] avcodec/pngdec: Check for fctl after idat

Fixes: out of array access
Fixes: 23554/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APNG_fuzzer-4796622520451072.fuzz

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/pngdec.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index ff3882a58d..647e7f0a74 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -984,6 +984,11 @@ static int decode_fctl_chunk(AVCodecContext *avctx, PNGDecContext *s,
         return AVERROR_INVALIDDATA;
     }
 
+    if (s->pic_state & PNG_IDAT) {
+        av_log(avctx, AV_LOG_ERROR, "fctl after IDAT\n");
+        return AVERROR_INVALIDDATA;
+    }
+
     s->last_w = s->cur_w;
     s->last_h = s->cur_h;
     s->last_x_offset = s->x_offset;