linux-kernel - Re: [PATCH] gpiolib: check for overflow when reading the 'ngpios' property

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Message-ID: <CAHp75Vfgsa5Ru5aA7Bx_mV--h-GFKSX9Uocf+njvh8Rc1yNTow@mail.gmail.com>
Date:   Mon, 7 Mar 2022 00:19:30 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: check for overflow when reading the 'ngpios' property

On Mon, Mar 7, 2022 at 12:11 AM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> The ngpio fields both in struct gpio_device as well as gpio_chip are
> 16-bit unsigned integers. Let's not risk an overflow and check if the
> property value represented as a 32-bit unsigned integer is not greater
> than U16_MAX.

...

> +               if (ngpios > U16_MAX) {
> +                       ret = EINVAL;
> +                       goto err_free_descs;
> +               }

I don't think it's a fatal error in this case. I would perhaps print a
warning and simply use a masked (which is done implicitly by an
assignment of the different type) value. Note, the above is buggy on
the buggy DTs, where the upper part of the value is not used. After
this patch you effectively make a regression on, yes, broken DTs.

-- 
With Best Regards,
Andy Shevchenko