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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@niedermayer.cc>
This commit is contained in:
Michael Niedermayer 2024-04-26 23:22:53 +02:00
parent d9699464c3
commit 091fdce87e
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1 changed files with 1 additions and 1 deletions
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libavcodec/pngdec.c
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@ -1218,7 +1218,7 @@ 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