linux-hardening - Re: [PATCH 5/5] mlxsw: spectrum_span: Annotate struct mlxsw_sp_span with __counted

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Message-ID: <CAFhGd8pCJa=qevxwhtQDvXMwdhF-33fV87m90GGaUFkOa6eRuA@mail.gmail.com>
Date: Tue, 3 Oct 2023 16:06:28 -0700
From: Justin Stitt <justinstitt@...gle.com>
To: Kees Cook <keescook@...omium.org>
Cc: Ido Schimmel <idosch@...dia.com>, Petr Machata <petrm@...dia.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH 5/5] mlxsw: spectrum_span: Annotate struct mlxsw_sp_span
 with __counted_by

On Fri, Sep 29, 2023 at 11:08 AM Kees Cook <keescook@...omium.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@...dia.com>
> Cc: Petr Machata <petrm@...dia.com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: netdev@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.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@...gle.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