Re: [PATCH 1/7] serial: sc16is7xx: fix snprintf format specifier in sc16is7xx_regmap_name()

[Hugo Villeneuve <hugo@hugovil.com>]

On Wed, 6 Dec 2023 14:29:39 +0800
kernel test robot <lkp@intel.com> wrote:

> Hi Hugo,
> 
> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on d804987153e7bedf503f8e4ba649afe52cfd7f6d]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Hugo-Villeneuve/serial-sc16is7xx-fix-snprintf-format-specifier-in-sc16is7xx_regmap_name/20231201-031413
> base:   d804987153e7bedf503f8e4ba649afe52cfd7f6d
> patch link:    https://lore.kernel.org/r/20231130191050.3165862-2-hugo%40hugovil.com
> patch subject: [PATCH 1/7] serial: sc16is7xx: fix snprintf format specifier in sc16is7xx_regmap_name()
> config: x86_64-buildonly-randconfig-001-20231201 (https://download.01.org/0day-ci/archive/20231206/202312061443.Cknef7Uq-lkp@intel.com/config)
> compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231206/202312061443.Cknef7Uq-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202312061443.Cknef7Uq-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
>    drivers/tty/serial/sc16is7xx.c: In function 'sc16is7xx_i2c_probe':
> >> drivers/tty/serial/sc16is7xx.c:1703:41: warning: '%u' directive output may be truncated writing between 1 and 10 bytes into a region of size 2 [-Wformat-truncation=]
>     1703 |         snprintf(buf, sizeof(buf), "port%u", port_id);
>          |                                         ^~
>    In function 'sc16is7xx_regmap_name',
>        inlined from 'sc16is7xx_i2c_probe' at drivers/tty/serial/sc16is7xx.c:1805:17:
>    drivers/tty/serial/sc16is7xx.c:1703:36: note: directive argument in the range [0, 4294967294]
>     1703 |         snprintf(buf, sizeof(buf), "port%u", port_id);
>          |                                    ^~~~~~~~
>    drivers/tty/serial/sc16is7xx.c:1703:9: note: 'snprintf' output between 6 and 15 bytes into a destination of size 6
>     1703 |         snprintf(buf, sizeof(buf), "port%u", port_id);
>          |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Hi,
the only solution I could find is to add this line just before snprintf:

    BUG_ON(port_id > MAX310X_MAX_PORTS);

it allows us to have the smallest buffer size possible.

One other solution would be to change port_id from "unsigned int"
to "u8", and increase the buffer by an additional 2 bytes to silence
the warning, but then wasting 2 bytes for each channel, like so:

static const char *max310x_regmap_name(u8 port_id)
{
    static char buf[
        sizeof(MAX310X_PORT_NAME_SUFFIX __stringify(UCHAR_MAX))];

I prefer solution 1, unless there is another solution that I am
unaware of.

Hugo.


> vim +1703 drivers/tty/serial/sc16is7xx.c
> 
>   1698	
>   1699	static const char *sc16is7xx_regmap_name(unsigned int port_id)
>   1700	{
>   1701		static char buf[6];
>   1702	
> > 1703		snprintf(buf, sizeof(buf), "port%u", port_id);
>   1704	
>   1705		return buf;
>   1706	}
>   1707	
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
> 


-- 
Hugo Villeneuve