Re: [FFmpeg-devel] [PATCH 2/3] avformat/evcdec: Check that enough data has been read

[James Almer <jamrial@gmail.com>]

On 7/6/2023 6:08 PM, Andreas Rheinhardt wrote:
> Fixes potential use of uninitialized values
> in evc_read_nal_unit_length().
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>   libavformat/evcdec.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/libavformat/evcdec.c b/libavformat/evcdec.c
> index 9886542311..0f464930f7 100644
> --- a/libavformat/evcdec.c
> +++ b/libavformat/evcdec.c
> @@ -162,6 +162,8 @@ static int evc_read_packet(AVFormatContext *s, AVPacket *pkt)
>           ret = avio_read(s->pb, buf, EVC_NALU_LENGTH_PREFIX_SIZE);
>           if (ret < 0)
>               return ret;
> +        if (ret != EVC_NALU_LENGTH_PREFIX_SIZE)
> +            return AVERROR_INVALIDDATA;

There's a ffio_ensure_seekback() for EVC_NALU_LENGTH_PREFIX_SIZE bytes 
immediately before the avio_read() call. Shouldn't that be enough to 
guarantee that much can be read?

Also, you can just pass ret to evc_read_nal_unit_length() below instead 
of adding this check here. It will return an error if it's < 
EVC_NALU_LENGTH_PREFIX_SIZE.

>   
>           nalu_size = evc_read_nal_unit_length(buf, EVC_NALU_LENGTH_PREFIX_SIZE);
>           if (!nalu_size || nalu_size > INT_MAX)
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