linux-hardening - Re: [PATCH] net/mlx5: Annotate struct mlx5_flow_handle with __counted

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Date: Tue, 3 Oct 2023 16:26:35 -0700
From: Justin Stitt <justinstitt@...gle.com>
To: Kees Cook <keescook@...omium.org>
Cc: Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>, 
	"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, 
	linux-rdma@...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] net/mlx5: Annotate struct mlx5_flow_handle with __counted_by

On Tue, Oct 3, 2023 at 4:17 PM 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 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 mlx5_flow_handle.
>
> Cc: Saeed Mahameed <saeedm@...dia.com>
> Cc: Leon Romanovsky <leon@...nel.org>
> 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
> Cc: linux-rdma@...r.kernel.org
> Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/fs_core.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/fs_core.h b/drivers/net/ethernet/mellanox/mlx5/core/fs_core.h
> index 4aed1768b85f..78eb6b7097e1 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/fs_core.h
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/fs_core.h
> @@ -181,7 +181,7 @@ struct mlx5_flow_rule {
>
>  struct mlx5_flow_handle {
>         int num_rules;
> -       struct mlx5_flow_rule *rule[];
> +       struct mlx5_flow_rule *rule[] __counted_by(num_rules);
>  };

Great patch!

handle->num_rules is properly assigned to before handle->rule
has any accesses.

        handle = alloc_handle((dest_num) ? dest_num : 1);

then

        static struct mlx5_flow_handle *alloc_handle(int num_rules) {
                ...
               handle->num_rules = num_rules;

then

        handle->rule[i] = rule;


Reviewed-by: Justin Stitt <justinstitt@...gle.com>
>
>  /* Type of children is mlx5_flow_group */
> --
> 2.34.1
>
>
Thanks
Justin