Re: [FFmpeg-devel] [PATCH] avformat: add CRI USM demuxer

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Paul B Mahol:
> 
> +    chunk_type = avio_rb32(pb);
> +    chunk_size = avio_rb32(pb);

You are not checking whether the chunk here exceeds its containing chunk.

> 
> +    av_fast_malloc(&usm->header, &usm->header_size,
> +                   chunk_size + AV_INPUT_BUFFER_PADDING_SIZE);
> +    if (!usm->header)
> +        return AVERROR(ENOMEM);

The bytestream2 API does not rely on the buffer being padded at all.

> 
> +    bytestream2_skip(&sgb, string_offset);

This is unnecessary, because you seek with an absolute offset lateron
anyway before using sgb.

> 
> +        bytestream2_seek(&sgb, string_offset + offset, SEEK_SET);
> +        while (bytestream2_get_bytes_left(&sgb) > 0) {
> +            key[n] = bytestream2_get_byte(&sgb);
> +            if (!key[n])
> +                break;
> +            if (n >= sizeof(key) - 1)
> +                break;
> +            n++;
> +        }
> +        key[n] = '\0';

IMO this would be easier with strnlen(), avoiding sgb altogether.
You would of course need to explicitly check that you are not
overreading, but that is good practice anyway.

> 
> +    chunk_start = avio_tell(pb);
> +    avio_skip(pb, 1);
> +    payload_offset = avio_r8(pb);
> +    padding_size = avio_rb16(pb);
> +    stream_index = avio_r8(pb);
> +    avio_skip(pb, 2);
> +    payload_type = avio_r8(pb);
> +    frame_time = avio_rb32(pb);
> +    frame_rate = avio_rb32(pb);
> +    avio_skip(pb, 8);

payload_offset and frame_time are set-but-unused; this might lead to
compiler warnings.

> +        if (usm->ch[is_audio][stream_index].used == 1) {
> +            uint32_t pkt_size = chunk_size - (avio_tell(pb) - chunk_start);
> +

This is unnecessary: Unless we already had a read error, pkt_size is
chunk_size - (1 + 1 + 2 + 1 + 2 + 1 + 4 + 4 + 8).

(Notice that in case padding_size is > 0, it will be part of the packet
with the current code; not sure if that is an issue.)

> 
> +
> +    avio_skip(pb, padding_size);
> +    avio_skip(pb, chunk_size - (avio_tell(pb) - chunk_start));
> +

Simpler to just use avio_seek(pb, chunk_start + chunk_size, SEEK_SET);

- Andreas

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