linux-hardening - Re: [PATCH] w1: Split memcpy() of struct cn

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Date:   Mon, 26 Sep 2022 20:19:26 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Evgeniy Polyakov <zbr@...emap.net>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] w1: Split memcpy() of struct cn_msg flexible array

On Mon, Sep 26, 2022 at 05:39:27PM -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: Evgeniy Polyakov <zbr@...emap.net>
> Signed-off-by: Kees Cook <keescook@...omium.org>

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

Thanks!
--
Gustavo

> ---
>  drivers/w1/w1_netlink.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/w1/w1_netlink.c b/drivers/w1/w1_netlink.c
> index fa490aa4407c..db110cc442b1 100644
> --- a/drivers/w1/w1_netlink.c
> +++ b/drivers/w1/w1_netlink.c
> @@ -611,7 +611,8 @@ static void w1_cn_callback(struct cn_msg *cn, struct netlink_skb_parms *nsp)
>  		}
>  		atomic_set(&block->refcnt, 1);
>  		block->portid = nsp->portid;
> -		memcpy(&block->request_cn, cn, sizeof(*cn) + cn->len);
> +		block->request_cn = *cn;
> +		memcpy(block->request_cn.data, cn->data, cn->len);
>  		node = (struct w1_cb_node *)(block->request_cn.data + cn->len);
>  
>  		/* Sneeky, when not bundling, reply_size is the allocated space
> -- 
> 2.34.1
>