[FFmpeg-devel] [PATCH] avcodec/vvcdec: ff_vvc_frame_submit, avoid initializing task twice.

[Frank Plowman]

On 21/04/2024 15:52, Nuo Mi wrote:
> For some error bitstreams, a CTU belongs to two slices/entry points.
> If the decoder initializes and submmits the CTU task twice, it may crash the program
> or cause it to enter an infinite loop.
> 
> Reported-by: Frank Plowman <post at frankplowman.com>
> ---
>  libavcodec/vvc/dec.c    |  7 +++++--
>  libavcodec/vvc/thread.c | 43 ++++++++++++++++++++++++++++-------------
>  libavcodec/vvc/thread.h |  2 +-
>  3 files changed, 36 insertions(+), 16 deletions(-)
> 
> diff --git a/libavcodec/vvc/dec.c b/libavcodec/vvc/dec.c
> index 6aeec27eaf..4f7d184e43 100644
> --- a/libavcodec/vvc/dec.c
> +++ b/libavcodec/vvc/dec.c
> @@ -893,10 +893,13 @@ static int wait_delayed_frame(VVCContext *s, AVFrame *output, int *got_output)
>  
>  static int submit_frame(VVCContext *s, VVCFrameContext *fc, AVFrame *output, int *got_output)
>  {
> -    int ret;
> +    int ret = ff_vvc_frame_submit(s, fc);
> +    if (ret < 0)
> +        return ret;
> +
>      s->nb_frames++;
>      s->nb_delayed++;
> -    ff_vvc_frame_submit(s, fc);
> +
>      if (s->nb_delayed >= s->nb_fcs) {
>          if ((ret = wait_delayed_frame(s, output, got_output)) < 0)
>              return ret;
> diff --git a/libavcodec/vvc/thread.c b/libavcodec/vvc/thread.c
> index 01c3ff75b1..3b27811db2 100644
> --- a/libavcodec/vvc/thread.c
> +++ b/libavcodec/vvc/thread.c
> @@ -124,11 +124,17 @@ static void task_init(VVCTask *t, VVCTaskStage stage, VVCFrameContext *fc, const
>      atomic_store(&t->target_inter_score, 0);
>  }
>  
> -static void task_init_parse(VVCTask *t, SliceContext *sc, EntryPoint *ep, const int ctu_idx)
> +static int task_init_parse(VVCTask *t, SliceContext *sc, EntryPoint *ep, const int ctu_idx)
>  {
> +    if (t->sc) {
> +        // the task already inited, error bitstream
> +        return AVERROR_INVALIDDATA;
> +    }
>      t->sc      = sc;
>      t->ep      = ep;
>      t->ctu_idx = ctu_idx;
> +
> +    return 0;
>  }
>  
>  static uint8_t task_add_score(VVCTask *t, const VVCTaskStage stage)
> @@ -758,24 +764,35 @@ static void submit_entry_point(VVCContext *s, VVCFrameThread *ft, SliceContext *
>      frame_thread_add_score(s, ft, t->rx, t->ry, VVC_TASK_STAGE_PARSE);
>  }
>  
> -void ff_vvc_frame_submit(VVCContext *s, VVCFrameContext *fc)
> +int ff_vvc_frame_submit(VVCContext *s, VVCFrameContext *fc)
>  {
>      VVCFrameThread *ft = fc->ft;
>  
> -    for (int i = 0; i < fc->nb_slices; i++) {
> -        SliceContext *sc = fc->slices[i];
> -        for (int j = 0; j < sc->nb_eps; j++) {
> -            EntryPoint *ep = sc->eps + j;
> -            for (int k = ep->ctu_start; k < ep->ctu_end; k++) {
> -                const int rs = sc->sh.ctb_addr_in_curr_slice[k];
> -                VVCTask *t   = ft->tasks + rs;
> -
> -                task_init_parse(t, sc, ep, k);
> -                check_colocation(s, t);
> +    // We'll handle this in two passes:
> +    // Pass 0 to initialize tasks with parser, this will help detect bit stream error
> +    // Pass 1 to shedule location check and submit the entry point
> +    for (int pass = 0; pass < 2; pass++) {
> +        for (int i = 0; i < fc->nb_slices; i++) {
> +            SliceContext *sc = fc->slices[i];
> +            for (int j = 0; j < sc->nb_eps; j++) {
> +                EntryPoint *ep = sc->eps + j;
> +                for (int k = ep->ctu_start; k < ep->ctu_end; k++) {
> +                    const int rs = sc->sh.ctb_addr_in_curr_slice[k];
> +                    VVCTask *t   = ft->tasks + rs;
> +                    if (pass) {
> +                        check_colocation(s, t);
> +                    } else {
> +                        const int ret = task_init_parse(t, sc, ep, k);
> +                        if (ret < 0)
> +                            return ret;
> +                    }
> +                }
> +                if (pass)
> +                    submit_entry_point(s, ft, sc, ep);
>              }
> -            submit_entry_point(s, ft, sc, ep);
>          }
>      }
> +    return 0;
>  }
>  
>  int ff_vvc_frame_wait(VVCContext *s, VVCFrameContext *fc)
> diff --git a/libavcodec/vvc/thread.h b/libavcodec/vvc/thread.h
> index 55bb4ea244..8ac59b2ecf 100644
> --- a/libavcodec/vvc/thread.h
> +++ b/libavcodec/vvc/thread.h
> @@ -30,7 +30,7 @@ void ff_vvc_executor_free(struct AVExecutor **e);
>  
>  int ff_vvc_frame_thread_init(VVCFrameContext *fc);
>  void ff_vvc_frame_thread_free(VVCFrameContext *fc);
> -void ff_vvc_frame_submit(VVCContext *s, VVCFrameContext *fc);
> +int ff_vvc_frame_submit(VVCContext *s, VVCFrameContext *fc);
>  int ff_vvc_frame_wait(VVCContext *s, VVCFrameContext *fc);
>  
>  #endif // AVCODEC_VVC_THREAD_H

This patch fixes most of the fuzz bitstreams I have which enter infinite
loops, but also introduces a regression, turning some other bitstreams
which were okay before into infinite loops.

-- 
Frank