Re: [FFmpeg-devel] [PATCH] lavc/vvc: Validate alf_list indexes

[Nuo Mi <nuomi2021@gmail.com>]

On Sun, Feb 4, 2024 at 1:22 AM <post@frankplowman.com> wrote:

> From: Frank Plowman <post@frankplowman.com>
>
> Fixes crashes when decoding illegal bitstreams found by fuzzing.
>
> Signed-off-by: Frank Plowman <post@frankplowman.com>
> ---
>  libavcodec/vvc/vvc_ctu.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/libavcodec/vvc/vvc_ctu.c b/libavcodec/vvc/vvc_ctu.c
> index d166b16a19..f601c6c95e 100644
> --- a/libavcodec/vvc/vvc_ctu.c
> +++ b/libavcodec/vvc/vvc_ctu.c
> @@ -2207,7 +2207,7 @@ static void hls_sao(VVCLocalContext *lc, const int
> rx, const int ry)
>      }
>  }
>
> -static void alf_params(VVCLocalContext *lc, const int rx, const int ry)
> +static int alf_params(VVCLocalContext *lc, const int rx, const int ry)
>  {
>      const VVCFrameContext *fc     = lc->fc;
>      const H266RawSliceHeader *sh  = lc->sc->sh.r;
> @@ -2233,6 +2233,11 @@ static void alf_params(VVCLocalContext *lc, const
> int rx, const int ry)
>                  c_idx == CB ? sh->sh_alf_cb_enabled_flag :
> sh->sh_alf_cr_enabled_flag;
>              if (alf_enabled_flag) {
>                  const VVCALF *aps =
> fc->ps.alf_list[sh->sh_alf_aps_id_chroma];
> +                if (!aps) {
> +                    // Slice header refers to an APS which does not exist
> +                    return AVERROR_INVALIDDATA;
> +                }
> +
>
Thank you Frank.
Since all "if conditions" are related to slices, could we perform the check
at sh_derive()?

>                  alf->ctb_flag[c_idx] = ff_vvc_alf_ctb_flag(lc, rx, ry,
> c_idx);
>                  alf->alf_ctb_filter_alt_idx[c_idx - 1] = 0;
>                  if (alf->ctb_flag[c_idx] && aps->num_chroma_filters > 1)
> @@ -2247,10 +2252,16 @@ static void alf_params(VVCLocalContext *lc, const
> int rx, const int ry)
>              alf->ctb_cc_idc[i] = 0;
>              if (cc_enabled[i]) {
>                  const VVCALF *aps = fc->ps.alf_list[cc_aps_id[i]];
> +                if (!aps) {
> +                    // Slice header refers to an APS which does not exist
> +                    return AVERROR_INVALIDDATA;
> +                }
>                  alf->ctb_cc_idc[i] = ff_vvc_alf_ctb_cc_idc(lc, rx, ry, i,
> aps->num_cc_filters[i]);
>              }
>          }
>      }
> +
> +    return 0;
>  }
>
>  static void deblock_params(VVCLocalContext *lc, const int rx, const int
> ry)
> @@ -2274,7 +2285,9 @@ static int hls_coding_tree_unit(VVCLocalContext *lc,
>      memset(lc->parse.chroma_qp_offset, 0,
> sizeof(lc->parse.chroma_qp_offset));
>
>      hls_sao(lc, x0 >> sps->ctb_log2_size_y, y0 >> sps->ctb_log2_size_y);
> -    alf_params(lc, x0 >> sps->ctb_log2_size_y, y0 >>
> sps->ctb_log2_size_y);
> +    ret = alf_params(lc, x0 >> sps->ctb_log2_size_y, y0 >>
> sps->ctb_log2_size_y);
> +    if (ret < 0)
> +        return ret;
>      deblock_params(lc, x0 >> sps->ctb_log2_size_y, y0 >>
> sps->ctb_log2_size_y);
>
>      if (IS_I(rsh) && sps->r->sps_qtbtt_dual_tree_intra_flag)
> --
> 2.43.0
>
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