Re: [PATCH 5/5] mlxsw: spectrum_span: Annotate struct mlxsw_sp_span with __counted_by

[Justin Stitt]

On Fri, Sep 29, 2023 at 11:08 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
>
> As found with Coccinelle[1], add __counted_by for struct mlxsw_sp_span.
>
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
>
> Cc: Ido Schimmel <idosch@xxxxxxxxxx>
> Cc: Petr Machata <petrm@xxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---

Great patch!

Crucially, span->entries_count is assigned before any flexible array
accesses.

        span->entries_count = entries_count;
        ...
        for (i = 0; i < mlxsw_sp->span->entries_count; i++)
                mlxsw_sp->span->entries[i].id = i;


Reviewed-by: Justin Stitt <justinstitt@xxxxxxxxxx>

>  drivers/net/ethernet/mellanox/mlxsw/spectrum_span.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_span.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_span.c
> index b3472fb94617..af50ff9e5f26 100644
> --- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_span.c
> +++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_span.c
> @@ -31,7 +31,7 @@ struct mlxsw_sp_span {
>         refcount_t policer_id_base_ref_count;
>         atomic_t active_entries_count;
>         int entries_count;
> -       struct mlxsw_sp_span_entry entries[];
> +       struct mlxsw_sp_span_entry entries[] __counted_by(entries_count);
>  };
>
>  struct mlxsw_sp_span_analyzed_port {
> --
> 2.34.1
>
>
Thanks
Justin