Re: [FFmpeg-devel] [PATCH 2/3] avcodec/mjpegbdec: Check for AVDISCARD_ALL

From: James Almer <jamrial@gmail.com>
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH 2/3] avcodec/mjpegbdec: Check for AVDISCARD_ALL
Date: Fri, 23 Dec 2022 15:39:35 -0300
Message-ID: <e535f7c6-8f8a-fb40-c46f-0a3064791be8@gmail.com> (raw)
In-Reply-To: <20221112234401.24158-2-michael@niedermayer.cc>

On 11/12/2022 8:44 PM, Michael Niedermayer wrote:
> Fixes: Assertion failure
> Fixes: 51825/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MJPEGB_fuzzer-6393802688692224
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>   libavcodec/mjpegbdec.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/mjpegbdec.c b/libavcodec/mjpegbdec.c
> index 98c64b44ca..a82a95d70a 100644
> --- a/libavcodec/mjpegbdec.c
> +++ b/libavcodec/mjpegbdec.c
> @@ -141,9 +141,10 @@ read_header:
>           av_log(avctx, AV_LOG_WARNING, "no picture\n");
>           return buf_size;
>       }
> -
>       av_frame_move_ref(rframe, s->picture_ptr);
>       s->got_picture = 0;
> +    if (avctx->skip_frame == AVDISCARD_ALL)
> +        return AVERROR(EAGAIN);

Decode callback decoders don't return EAGAIN. If they don't generate a 
frame but there was no error, then they return the amount of bytes 
consumed while ensuring got_frame is 0.

>       *got_frame = 1;
>   
>       if (!s->lossless && avctx->debug & FF_DEBUG_QP) {
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