linux-hardening - Re: [PATCH] mlxsw: core_acl_flex_actions: Split memcpy() of struct flow_action

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Date:   Mon, 26 Sep 2022 20:10:11 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
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,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] mlxsw: core_acl_flex_actions: Split memcpy() of struct
 flow_action_cookie flexible array

On Mon, Sep 26, 2022 at 05:40:33PM -0700, Kees Cook wrote:
> To work around a misbehavior of the compiler's ability to see into
> composite flexible array structs (as detailed in the coming memcpy()
> hardening series[1]), split the memcpy() of the header and the payload
> so no false positive run-time overflow warning will be generated.
> 
> [1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org
> 
> 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>


Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks!
--
Gustavo

> ---
>  drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_actions.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_actions.c b/drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_actions.c
> index 636db9a87457..9dfe7148199f 100644
> --- a/drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_actions.c
> +++ b/drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_actions.c
> @@ -737,8 +737,9 @@ mlxsw_afa_cookie_create(struct mlxsw_afa *mlxsw_afa,
>  	if (!cookie)
>  		return ERR_PTR(-ENOMEM);
>  	refcount_set(&cookie->ref_count, 1);
> -	memcpy(&cookie->fa_cookie, fa_cookie,
> -	       sizeof(*fa_cookie) + fa_cookie->cookie_len);
> +	cookie->fa_cookie = *fa_cookie;
> +	memcpy(cookie->fa_cookie.cookie, fa_cookie->cookie,
> +	       fa_cookie->cookie_len);
>  
>  	err = rhashtable_insert_fast(&mlxsw_afa->cookie_ht, &cookie->ht_node,
>  				     mlxsw_afa_cookie_ht_params);
> -- 
> 2.34.1
>