Re: [FFmpeg-devel] [PATCH] lavc/vvc: Validate IBC block vector

[Nuo Mi <nuomi2021@gmail.com>]

On Mon, Jun 24, 2024 at 9:31 PM Frank Plowman <post@frankplowman.com> wrote:

> From H.266 (V3) (09/2023) p. 321:
>
> It is a requirement of bitstream conformance that the luma block
> vector bvL shall obey the following constraints:
> - CtbSizeY is greater than or equal to
> ((yCb + (bvL[ 1 ] >> 4)) & (CtbSizeY − 1)) + cbHeight
>
> This patch checks this is true, which fixes crashes on fuzzed
> bitstreams.
>
> Signed-off-by: Frank Plowman <post@frankplowman.com>
> ---
>  libavcodec/vvc/intra.c  | 25 ++++++++++++++++++++++---
>  libavcodec/vvc/thread.c |  4 +---
>  2 files changed, 23 insertions(+), 6 deletions(-)
>
> diff --git a/libavcodec/vvc/intra.c b/libavcodec/vvc/intra.c
> index f77a012f09..11371db797 100644
> --- a/libavcodec/vvc/intra.c
> +++ b/libavcodec/vvc/intra.c
> @@ -624,15 +624,26 @@ static void intra_block_copy(const VVCLocalContext
> *lc, const int c_idx)
>      }
>  }
>
> -static void vvc_predict_ibc(const VVCLocalContext *lc)
> +static int vvc_predict_ibc(const VVCLocalContext *lc)
>  {
> -    const H266RawSPS *rsps = lc->fc->ps.sps->r;
> +    const VVCFrameContext *fc = lc->fc;
> +    const VVCSPS *sps         = lc->fc->ps.sps;
> +    const H266RawSPS *rsps    = sps->r;
> +    const CodingUnit *cu      = lc->cu;
> +    const Mv *bv              = &cu->pu.mi.mv[L0][0];
> +
> +    if (sps->ctb_size_y < ((cu->y0 + (bv->y >> 4)) & (sps->ctb_size_y -
> 1)) + cu->cb_height) {
> +        av_log(fc->log_ctx, AV_LOG_ERROR, "IBC region spans multiple
> CTBs.\n");
> +        return AVERROR_INVALIDDATA;
> +    }

Hi Frank,
Thank you for the patch.
Could we wrap it as a function and call it in ff_vvc_mvp_ibc and
ff_vvc_luma_mv_merge_ibc?
This will help us detect errors earlier.

>


>      intra_block_copy(lc, LUMA);
>      if (lc->cu->tree_type == SINGLE_TREE && rsps->sps_chroma_format_idc) {
>          intra_block_copy(lc, CB);
>          intra_block_copy(lc, CR);
>      }
> +
> +    return 0;
>  }
>
>  static void ibc_fill_vir_buf(const VVCLocalContext *lc, const CodingUnit
> *cu)
> @@ -678,7 +689,10 @@ int ff_vvc_reconstruct(VVCLocalContext *lc, const int
> rs, const int rx, const in
>          if (cu->ciip_flag)
>              ff_vvc_predict_ciip(lc);
>          else if (cu->pred_mode == MODE_IBC)
> -            vvc_predict_ibc(lc);
> +            ret = vvc_predict_ibc(lc);
> +        if (ret)
> +            goto fail;
> +
>          if (cu->coded_flag) {
>              ret = reconstruct(lc);
>          } else {
> @@ -687,10 +701,15 @@ int ff_vvc_reconstruct(VVCLocalContext *lc, const
> int rs, const int rx, const in
>              if (sps->r->sps_chroma_format_idc && cu->tree_type !=
> DUAL_TREE_LUMA)
>                  add_reconstructed_area(lc, CHROMA, cu->x0, cu->y0,
> cu->cb_width, cu->cb_height);
>          }
> +        if (ret)
> +            goto fail;
> +
>          if (sps->r->sps_ibc_enabled_flag)
>              ibc_fill_vir_buf(lc, cu);
>          cu = cu->next;
>      }
> +
> +fail:
>      ff_vvc_ctu_free_cus(ctu);
>      return ret;
>  }
> diff --git a/libavcodec/vvc/thread.c b/libavcodec/vvc/thread.c
> index 8777d380bf..5b01dd2d20 100644
> --- a/libavcodec/vvc/thread.c
> +++ b/libavcodec/vvc/thread.c
> @@ -454,9 +454,7 @@ static int run_inter(VVCContext *s, VVCLocalContext
> *lc, VVCTask *t)
>
>  static int run_recon(VVCContext *s, VVCLocalContext *lc, VVCTask *t)
>  {
> -    ff_vvc_reconstruct(lc, t->rs, t->rx, t->ry);
> -
> -    return 0;
> +    return ff_vvc_reconstruct(lc, t->rs, t->rx, t->ry);
>  }
>
>  static int run_lmcs(VVCContext *s, VVCLocalContext *lc, VVCTask *t)
> --
> 2.45.1
>
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