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

Justin Stitt
2023-10-03T23:06:45Z

On Fri, Sep 29, 2023 at 11:08 AM Kees Cook <keescook@chromium.org> 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@nvidia.com>
> Cc: Petr Machata <petrm@nvidia.com>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: netdev@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---

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@google.com>

> 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