Re: [PATCH 18/22] gpio: acpi: fix string overflow for large pin numbers

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Arnd Bergmann <arnd@arndb.de>,
	linux-kernel@vger.kernel.org,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Linus Walleij <linus.walleij@linaro.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Guenter Roeck <linux@roeck-us.net>,
	akpm@linux-foundation.org, netdev@vger.kernel.org,
	"David S . Miller" <davem@davemloft.net>,
	"James E . J . Bottomley" <jejb@linux.vnet.ibm.com>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	linux-scsi@vger.kernel.org, x86@kernel.org,
	Hans de Goede <hdegoede@redhat.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Wei Yongjun <weiyongjun1@huawei.com>,
	linux-gpio@vger.kernel.org, linux-acpi@vger.kernel.org
Subject: Re: [PATCH 18/22] gpio: acpi: fix string overflow for large pin numbers
Date: Fri, 14 Jul 2017 15:52:20 +0300	[thread overview]
Message-ID: <1500036740.29303.7.camel@linux.intel.com> (raw)
In-Reply-To: <20170714120720.906842-19-arnd@arndb.de>

On Fri, 2017-07-14 at 14:07 +0200, Arnd Bergmann wrote:
> gcc-7 notices that the pin_table is an array of 16-bit numbers,
> but we assume it can be printed as a two-character hexadecimal
> string:
> 
> drivers/gpio/gpiolib-acpi.c: In function
> 'acpi_gpiochip_request_interrupt':
> drivers/gpio/gpiolib-acpi.c:206:24: warning: '%02X' directive writing
> between 2 and 4 bytes into a region of size 3 [-Wformat-overflow=]
>    sprintf(ev_name, "_%c%02X",
>                         ^~~~
> drivers/gpio/gpiolib-acpi.c:206:20: note: directive argument in the
> range [0, 65535]
>    sprintf(ev_name, "_%c%02X",
>                     ^~~~~~~~~
> drivers/gpio/gpiolib-acpi.c:206:3: note: 'sprintf' output between 5
> and 7 bytes into a destination of size 5
>    sprintf(ev_name, "_%c%02X",
>    ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>     agpio->triggering == ACPI_EDGE_SENSITIVE ? 'E' : 'L',
>     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     pin);
>     ~~~~

This is obviously a false positive warning.

Here we have
int pin = u16 pin_table[0] <= 255 (implying >= 0).

I see few options how to make it more clear
1) your proposal;
2) use "%02hhX" instead;
3) use if (ret >= 0 && ret <= 255) condition.

I would choose one of the 2-3.

In case gcc will complain about 3), file a bug to gcc crazy warning.

> 
> This can't be right, so this changes it to truncate the number to
> an 8-bit pin number.
> 
> Fixes: 0d1c28a449c6 ("gpiolib-acpi: Add ACPI5 event model support to
> gpio.")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/gpio/gpiolib-acpi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpio/gpiolib-acpi.c b/drivers/gpio/gpiolib-acpi.c
> index c9b42dd12dfa..c3faea724af8 100644
> --- a/drivers/gpio/gpiolib-acpi.c
> +++ b/drivers/gpio/gpiolib-acpi.c
> @@ -205,7 +205,7 @@ static acpi_status
> acpi_gpiochip_request_interrupt(struct acpi_resource *ares,
>  		char ev_name[5];
>  		sprintf(ev_name, "_%c%02X",
>  			agpio->triggering == ACPI_EDGE_SENSITIVE ?
> 'E' : 'L',
> -			pin);
> +			(u8)pin);
>  		if (ACPI_SUCCESS(acpi_get_handle(handle, ev_name,
> &evt_handle)))
>  			handler = acpi_gpio_irq_handler;
>  	}

-- 
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy