linux-kernel - Re: [PATCH] gpiolib: cdev: Annotate struct linereq with __counted

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Date:   Sat, 23 Sep 2023 10:34:44 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Kees Cook <keescook@...omium.org>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        Andy Shevchenko <andy@...nel.org>, linux-gpio@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] gpiolib: cdev: Annotate struct linereq with __counted_by



On 9/22/23 11:52, Kees Cook 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 checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> As found with Coccinelle[1], add __counted_by for struct linereq.
> Additionally, since the element count member must be set before accessing
> the annotated flexible array member, move its initialization earlier.
> 
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> 
> Cc: Linus Walleij <linus.walleij@...aro.org>
> Cc: Bartosz Golaszewski <brgl@...ev.pl>
> Cc: Andy Shevchenko <andy@...nel.org>
> Cc: linux-gpio@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

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

Thanks
-- 
Gustavo

> ---
>   drivers/gpio/gpiolib-cdev.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> index e39d344feb28..31fc71a612c2 100644
> --- a/drivers/gpio/gpiolib-cdev.c
> +++ b/drivers/gpio/gpiolib-cdev.c
> @@ -572,7 +572,7 @@ struct linereq {
>   	DECLARE_KFIFO_PTR(events, struct gpio_v2_line_event);
>   	atomic_t seqno;
>   	struct mutex config_mutex;
> -	struct line lines[];
> +	struct line lines[] __counted_by(num_lines);
>   };
>   
>   #define GPIO_V2_LINE_BIAS_FLAGS \
> @@ -1656,6 +1656,7 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
>   	lr = kzalloc(struct_size(lr, lines, ulr.num_lines), GFP_KERNEL);
>   	if (!lr)
>   		return -ENOMEM;
> +	lr->num_lines = ulr.num_lines;
>   
>   	lr->gdev = gpio_device_get(gdev);
>   
> @@ -1684,7 +1685,6 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
>   		lr->event_buffer_size = GPIO_V2_LINES_MAX * 16;
>   
>   	atomic_set(&lr->seqno, 0);
> -	lr->num_lines = ulr.num_lines;
>   
>   	/* Request each GPIO */
>   	for (i = 0; i < ulr.num_lines; i++) {