Re: [FFmpeg-devel] [PATCH 2/4] avformat/mov: Add special case for slow duplication loop in mov_read_trun()

[Marton Balint <cus@passwd.hu>]

On Sat, 18 Jun 2022, Michael Niedermayer wrote:

> This extra code is ugly, better solution is welcome

If you work on fixing these issues, it is kind of your job to find an 
elegant and maintainable solution. If you can't find one with reasonable 
amount of work, then IMHO it is better to leave the timeout issue in the 
code.

Regards,
Marton

>
> Fixes: Timeout
> Fixes: 45700/clusterfuzz-testcase-minimized-ffmpeg_IO_DEMUXER_fuzzer-6141847792123904
>
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
> libavformat/mov.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 69 insertions(+)
>
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index c93e13c8cd..3d9e866d4e 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -5092,6 +5092,7 @@ static int mov_read_trun(MOVContext *c, AVIOContext *pb, MOVAtom atom)
>     if (index_entry_pos > 0)
>         prev_dts = sti->index_entries[index_entry_pos-1].timestamp;
>
> +    if (flags & 0xF00) {
>     for (i = 0; i < entries && !pb->eof_reached; i++) {
>         unsigned sample_size = frag->size;
>         int sample_flags = i ? frag->flags : first_sample_flags;
> @@ -5166,6 +5167,74 @@ static int mov_read_trun(MOVContext *c, AVIOContext *pb, MOVAtom atom)
>             sc->nb_frames_for_fps ++;
>         }
>     }
> +    } else {
> +        unsigned sample_size = frag->size;
> +        unsigned sample_duration = frag->duration;
> +
> +        if (pts != AV_NOPTS_VALUE) {
> +            dts = pts - sc->dts_shift - sc->time_offset;
> +            av_log(c->fc, AV_LOG_DEBUG,
> +                "pts %"PRId64" calculated dts %"PRId64
> +                " sc->dts_shift %d ctts.duration %d"
> +                " sc->time_offset %"PRId64
> +                " flags & MOV_TRUN_SAMPLE_CTS %d\n",
> +                pts, dts,
> +                sc->dts_shift, 0,
> +                sc->time_offset, 0);
> +        }
> +
> +        if (av_sat_add64(dts, sample_duration * entries) != dts + (uint64_t)sample_duration * entries)
> +            return AVERROR_INVALIDDATA;
> +
> +        for (i = 0; i < entries && !pb->eof_reached; i++) {
> +            int sample_flags = i ? frag->flags : first_sample_flags;
> +            int keyframe = 0;
> +            int index_entry_flags = 0;
> +
> +            if (st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO)
> +                keyframe = 1;
> +            else
> +                keyframe =
> +                    !(sample_flags & (MOV_FRAG_SAMPLE_FLAG_IS_NON_SYNC |
> +                                    MOV_FRAG_SAMPLE_FLAG_DEPENDS_YES));
> +            if (keyframe) {
> +                distance = 0;
> +                index_entry_flags |= AVINDEX_KEYFRAME;
> +            }
> +            // Fragments can overlap in time.  Discard overlapping frames after
> +            // decoding.
> +            if (prev_dts >= dts)
> +                index_entry_flags |= AVINDEX_DISCARD_FRAME;
> +
> +            sti->index_entries[index_entry_pos].pos   = offset;
> +            sti->index_entries[index_entry_pos].timestamp = dts;
> +            sti->index_entries[index_entry_pos].size  = sample_size;
> +            sti->index_entries[index_entry_pos].min_distance = distance;
> +            sti->index_entries[index_entry_pos].flags = index_entry_flags;
> +
> +            sc->ctts_data[index_entry_pos].count = 1;
> +            sc->ctts_data[index_entry_pos].duration = 0;
> +            index_entry_pos++;
> +
> +            av_log(c->fc, AV_LOG_TRACE, "AVIndex stream %d, sample %d, offset %"PRIx64", dts %"PRId64", "
> +                    "size %u, distance %d, keyframe %d\n", st->index,
> +                    index_entry_pos, offset, dts, sample_size, distance, keyframe);
> +            distance++;
> +            dts += sample_duration;
> +            offset += sample_size;
> +            sc->data_size += sample_size;
> +
> +            if (sample_duration <= INT64_MAX - sc->duration_for_fps &&
> +                1 <= INT_MAX - sc->nb_frames_for_fps
> +            ) {
> +                sc->duration_for_fps += sample_duration;
> +                sc->nb_frames_for_fps ++;
> +            }
> +        }
> +
> +    }
> +
> +
>     if (frag_stream_info)
>         frag_stream_info->next_trun_dts = dts + sc->time_offset;
>     if (i < entries) {
> -- 
> 2.17.1
>
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