[FFmpeg-devel] [PATCH 2/2 v2] avformat/matroskadec: use av_fast_realloc to reallocate ebml list arrays

[Andreas Rheinhardt]

James Almer:
> Speeds up the process considerably.
> 
> Fixes ticket #8109.
> 
> Suggested-by: nevcairiel
> Suggested-by: cehoyos
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
>  libavformat/matroskadec.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
> index 439ee462a5..0f227eb33d 100644
> --- a/libavformat/matroskadec.c
> +++ b/libavformat/matroskadec.c
> @@ -110,6 +110,7 @@ typedef const struct EbmlSyntax {
>  
>  typedef struct EbmlList {
>      int nb_elem;
> +    unsigned int alloc_elem_size;
>      void *elem;
>  } EbmlList;
>  
> @@ -1236,8 +1237,14 @@ static int ebml_parse(MatroskaDemuxContext *matroska,
>          data = (char *) data + syntax->data_offset;
>          if (syntax->list_elem_size) {
>              EbmlList *list = data;
> -            void *newelem = av_realloc_array(list->elem, list->nb_elem + 1,
> -                                                   syntax->list_elem_size);
> +            void *newelem;
> +
> +            if ((unsigned)list->nb_elem + 1 >= UINT_MAX / syntax->list_elem_size)
> +                return AVERROR(ENOMEM);
> +
> +            newelem = av_fast_realloc(list->elem,
> +                                      &list->alloc_elem_size,
> +                                      (list->nb_elem + 1) * syntax->list_elem_size);
If this fails, list->alloc_elem_size will be zero, yet list->elem and
list->nb_elem might be non NULL/zero. I actually think that this will
probably work, but it is nevertheless ugly.

- Andreas