linux-kernel - Re: [PATCH][next] staging: greybus: i2c: Use struct_size() helper in gb_i2c_operation

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Message-ID: <202201241213.82E7D9F598@keescook>
Date:   Mon, 24 Jan 2022 12:19:03 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Viresh Kumar <vireshk@...nel.org>, Johan Hovold <johan@...nel.org>,
        Alex Elder <elder@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        greybus-dev@...ts.linaro.org, linux-staging@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] staging: greybus: i2c: Use struct_size() helper in
 gb_i2c_operation_create()

On Fri, Jan 21, 2022 at 04:22:50PM -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:
> drivers/staging/greybus/i2c.c:111:24: 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>
> ---
>  drivers/staging/greybus/i2c.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/greybus/i2c.c b/drivers/staging/greybus/i2c.c
> index de2f6516da09..9dfc6791c20e 100644
> --- a/drivers/staging/greybus/i2c.c
> +++ b/drivers/staging/greybus/i2c.c
> @@ -108,9 +108,7 @@ gb_i2c_operation_create(struct gb_connection *connection,
>  		else
>  			data_out_size += (u32)msg->len;
>  
> -	request_size = sizeof(*request);
> -	request_size += msg_count * sizeof(*op);
> -	request_size += data_out_size;
> +	request_size = struct_size(request, ops, msg_count) + data_out_size;

This could still overflow if struct_size() returns SIZE_MAX. Perhaps:

	if (check_add_overflow(struct_size(request, ops, msg_count),
			       data_out_size, &request_size))
		request_size = SIZE_MAX;

I should brush off the saturating arithmetic helpers series:
https://lore.kernel.org/all/20210920180853.1825195-1-keescook@chromium.org/

>  
>  	/* Response consists only of incoming data */
>  	operation = gb_operation_create(connection, GB_I2C_TYPE_TRANSFER,
> -- 
> 2.27.0
> 

-- 
Kees Cook