linux-kernel - Re: [PATCH v2][next] ALSA: usb-audio: scarlett2: Use struct_size() helper in scarlett2

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Date:   Thu, 20 Jan 2022 15:22:11 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     "Geoffrey D. Bennett" <g@...vu>, Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2][next] ALSA: usb-audio: scarlett2: Use struct_size()
 helper in scarlett2_usb()

On Thu, Jan 20, 2022 at 03:16:00PM -0600, Gustavo A. R. Silva wrote:
> Make use of the struct_size() helper instead of an open-coded version,
> in order to avoid any potential type mistakes or integer overflows that,
> in the worst scenario, could lead to heap overflows.
> 
> Also, address the following sparse warnings:
> sound/usb/mixer_scarlett_gen2.c:1064:28: warning: using sizeof on a flexible structure
> sound/usb/mixer_scarlett_gen2.c:1065:29: warning: using sizeof on a flexible structure
> 
> Link: https://github.com/KSPP/linux/issues/174
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Looks good to me!

Reviewed-by: Kees Cook <keescook@...omium.org>

> ---
> Changes in v2:
>  - Use correct format specifier %zu for type size_t argument.
> 
>  sound/usb/mixer_scarlett_gen2.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c
> index 53ebabf42472..7ff8a4817c67 100644
> --- a/sound/usb/mixer_scarlett_gen2.c
> +++ b/sound/usb/mixer_scarlett_gen2.c
> @@ -1061,9 +1061,9 @@ static int scarlett2_usb(
>  {
>  	struct scarlett2_data *private = mixer->private_data;
>  	struct usb_device *dev = mixer->chip->dev;
> -	u16 req_buf_size = sizeof(struct scarlett2_usb_packet) + req_size;
> -	u16 resp_buf_size = sizeof(struct scarlett2_usb_packet) + resp_size;
>  	struct scarlett2_usb_packet *req, *resp = NULL;
> +	size_t req_buf_size = struct_size(req, data, req_size);
> +	size_t resp_buf_size = struct_size(resp, data, resp_size);
>  	int err;
>  
>  	req = kmalloc(req_buf_size, GFP_KERNEL);
> @@ -1111,7 +1111,7 @@ static int scarlett2_usb(
>  		usb_audio_err(
>  			mixer->chip,
>  			"Scarlett Gen 2/3 USB response result cmd %x was %d "
> -			"expected %d\n",
> +			"expected %zu\n",
>  			cmd, err, resp_buf_size);
>  		err = -EINVAL;
>  		goto unlock;
> -- 
> 2.27.0
> 

-- 
Kees Cook