linux-hardening - Re: [PATCH][next] hostap: Add __counted_by for struct prism2_download_data and use struct

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Date: Mon, 9 Oct 2023 12:54:28 -0700
From: Kees Cook <keescook@...omium.org>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Kalle Valo <kvalo@...nel.org>, linux-wireless@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] hostap: Add __counted_by for struct
 prism2_download_data and use struct_size()

On Mon, Oct 09, 2023 at 01:41:18PM -0600, Gustavo A. R. Silva 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).
> 
> While there, use struct_size() helper, instead of the open-coded
> version, to calculate the size for the allocation of the whole
> flexible structure, including of course, the flexible-array member.
> 
> This code was found with the help of Coccinelle, and audited and
> fixed manually.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  drivers/net/wireless/intersil/hostap/hostap_download.c | 3 +--
>  drivers/net/wireless/intersil/hostap/hostap_wlan.h     | 2 +-
>  2 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/wireless/intersil/hostap/hostap_download.c b/drivers/net/wireless/intersil/hostap/hostap_download.c
> index 3672291ced5c..5e5bada28b5b 100644
> --- a/drivers/net/wireless/intersil/hostap/hostap_download.c
> +++ b/drivers/net/wireless/intersil/hostap/hostap_download.c
> @@ -732,8 +732,7 @@ static int prism2_download(local_info_t *local,
>  		goto out;
>  	}
>  
> -	dl = kzalloc(sizeof(*dl) + param->num_areas *
> -		     sizeof(struct prism2_download_data_area), GFP_KERNEL);
> +	dl = kzalloc(struct_size(dl, data, param->num_areas), GFP_KERNEL);
>  	if (dl == NULL) {
>  		ret = -ENOMEM;
>  		goto out;
> diff --git a/drivers/net/wireless/intersil/hostap/hostap_wlan.h b/drivers/net/wireless/intersil/hostap/hostap_wlan.h
> index c25cd21d18bd..f71c0545c0be 100644
> --- a/drivers/net/wireless/intersil/hostap/hostap_wlan.h
> +++ b/drivers/net/wireless/intersil/hostap/hostap_wlan.h
> @@ -617,7 +617,7 @@ struct prism2_download_data {
>  		u32 addr; /* wlan card address */
>  		u32 len;
>  		u8 *data; /* allocated data */
> -	} data[];
> +	} data[] __counted_by(num_areas);
>  };

Should this be considered a v2 of:
https://lore.kernel.org/linux-hardening/94848cc3-6f5c-46d7-8cc7-98a4f10865b3@embeddedor.com/

?

Yours is more complete since it includes the struct_size() change...

-- 
Kees Cook