[FFmpeg-cvslog] avcodec/pngdec: Check last AVFrame before deref

[Michael Niedermayer]

ffmpeg | branch: release/5.1 | Michael Niedermayer <michael at niedermayer.cc> | Fri Apr 26 23:22:53 2024 +0200| [dc9d2eb69d553e3bb144f2253def6b8e6ad4ff7d] | committer: Michael Niedermayer

avcodec/pngdec: Check last AVFrame before deref

Fixes: NULL pointer dereference
Fixes: 68184/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APNG_fuzzer-4926478069334016

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit 091fdce87e88c8622d8af89ffa6cbb0dc20c3816)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=dc9d2eb69d553e3bb144f2253def6b8e6ad4ff7d
---

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

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index b085154fbc..0da2ae8b6b 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -1027,7 +1027,7 @@ static int decode_fctl_chunk(AVCodecContext *avctx, PNGDecContext *s,
         return AVERROR_INVALIDDATA;
     }
 
-    if ((sequence_number == 0 || !s->last_picture.f->data[0]) &&
+    if ((sequence_number == 0 || !s->last_picture.f) &&
         dispose_op == APNG_DISPOSE_OP_PREVIOUS) {
         // No previous frame to revert to for the first frame
         // Spec says to just treat it as a APNG_DISPOSE_OP_BACKGROUND