linux-hardening - Re: [PATCH] s390/qeth: Split memcpy() of struct qeth_ipacmd_addr

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Message-ID: <YzJO0f7v7N4Z+9Dk@work>
Date:   Mon, 26 Sep 2022 20:16:01 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Alexandra Winter <wintera@...ux.ibm.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] s390/qeth: Split memcpy() of struct
 qeth_ipacmd_addr_change flexible array

On Mon, Sep 26, 2022 at 05:39:53PM -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: Alexandra Winter <wintera@...ux.ibm.com>
> Cc: Wenjia Zhang <wenjia@...ux.ibm.com>
> Cc: Heiko Carstens <hca@...ux.ibm.com>
> Cc: Vasily Gorbik <gor@...ux.ibm.com>
> Cc: Alexander Gordeev <agordeev@...ux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@...ux.ibm.com>
> Cc: Sven Schnelle <svens@...ux.ibm.com>
> Cc: linux-s390@...r.kernel.org
> 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/s390/net/qeth_l2_main.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/s390/net/qeth_l2_main.c b/drivers/s390/net/qeth_l2_main.c
> index 2d4436cbcb47..0ce635b7b472 100644
> --- a/drivers/s390/net/qeth_l2_main.c
> +++ b/drivers/s390/net/qeth_l2_main.c
> @@ -1530,8 +1530,8 @@ static void qeth_addr_change_event(struct qeth_card *card,
>  	else
>  		INIT_DELAYED_WORK(&data->dwork, qeth_l2_dev2br_worker);
>  	data->card = card;
> -	memcpy(&data->ac_event, hostevs,
> -			sizeof(struct qeth_ipacmd_addr_change) + extrasize);
> +	data->ac_event = *hostevs;
> +	memcpy(data->ac_event.entry, hostevs->entry, extrasize);
>  	queue_delayed_work(card->event_wq, &data->dwork, 0);
>  }
>  
> -- 
> 2.34.1
>