[FFmpeg-devel] [PATCH v2 2/2] lavc/vvc: Prevent overflow in chroma QP derivation

[Nuo Mi]

Hi Frank,
Thank you for the patch

On Wed, Jun 5, 2024 at 5:24 PM Frank Plowman <post at frankplowman.com> wrote:

> On the top of p. 112 in VVC (09/2023):
>
> It is a requirement of bitstream conformance that the values of
> qpInVal[ i ][ j ] and qpOutVal[ i ][ j ] shall be in the range
> of −QpBdOffset to 63, inclusive for i in the range of 0 to
>
Then, why do we not check −QpBdOffset?

> numQpTables − 1, inclusive, and j in the range of 0 to
> sps_num_points_in_qp_table_minus1[ i ] + 1, inclusive.
>
> Signed-off-by: Frank Plowman <post at frankplowman.com>
> ---
>  libavcodec/vvc/ps.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/libavcodec/vvc/ps.c b/libavcodec/vvc/ps.c
> index bfc3c121fd..c4f64d5da7 100644
> --- a/libavcodec/vvc/ps.c
> +++ b/libavcodec/vvc/ps.c
> @@ -101,9 +101,14 @@ static int sps_chroma_qp_table(VVCSPS *sps)
>
>          qp_out[0] = qp_in[0] = r->sps_qp_table_start_minus26[i] + 26;
>          for (int j = 0; j < num_points_in_qp_table; j++ ) {
> +            const uint8_t delta_qp_out =
> (r->sps_delta_qp_in_val_minus1[i][j] ^ r->sps_delta_qp_diff_val[i][j]);
>              delta_qp_in[j] = r->sps_delta_qp_in_val_minus1[i][j] + 1;
> +            if (qp_in[j] + delta_qp_in[j] > 63)
> +                return AVERROR(EINVAL);
>              qp_in[j+1] = qp_in[j] + delta_qp_in[j];
> -            qp_out[j+1] = qp_out[j] +
> (r->sps_delta_qp_in_val_minus1[i][j] ^ r->sps_delta_qp_diff_val[i][j]);
> +            if (qp_out[j] + delta_qp_out > 63)
> +                return AVERROR(EINVAL);
> +            qp_out[j+1] = qp_out[j] + delta_qp_out;
>
Instead of changing so many lines, we can  add 2 lines here
if (qp_in[j+1] < 63 ||  qp_out[j+1] < 63)
    return AVERROR(EINVAL);

>          }
>          sps->chroma_qp_table[i][qp_in[0] + off] = qp_out[0];
>          for (int k = qp_in[0] - 1 + off; k >= 0; k--)
> --
> 2.45.1
>
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