linux-hardening - Re: [PATCH v3] drivers/iio: Remove all strcpy() uses

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Message-ID: <CAHp75VfxYd0pS-WmE62F5w4SFWchDS=7iedaG1rY0Nc9+092RQ@mail.gmail.com>
Date:   Sat, 14 Aug 2021 13:08:48 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Len Baker <len.baker@....com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        David Laight <David.Laight@...lab.com>,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] drivers/iio: Remove all strcpy() uses

On Sat, Aug 14, 2021 at 12:06 PM Len Baker <len.baker@....com> wrote:
>
> strcpy() performs no bounds checking on the destination buffer. This
> could result in linear overflows beyond the end of the buffer, leading
> to all kinds of misbehaviors. So, remove all the uses and add
> devm_kstrdup() or devm_kasprintf() instead.
>
> This patch is an effort to clean up the proliferation of str*()
> functions in the kernel and a previous step in the path to remove
> the strcpy function from the kernel entirely [1].
>
> [1] https://github.com/KSPP/linux/issues/88

Thanks for an update, my comments below.

...

> This patch doesn't change the logic. I think it is better to use the
> current logic and not use always the plus and minus signs as suggested
> in the previous version. I don't like the idea that 0 has sign.

Agree on that, the safest way to go with.

...

>         const char *orient;
>         char *str;
>         int i;
> +       struct device *dev;

Please, keep this in reversed xmas tree order (longer lines first).

...

> +               dev = regmap_get_device(st->map);

I haven't checked the code in between, but maybe it's possible to move
an assignment directly to the definition block above.

...

> +                       /*
> +                        * The value is inverted according to the following

"to one of the"
And technically speaking "inversion" is not the same as negation
(which is "sign inversion").

> +                        * rules:
> +                        *
> +                        * 1) Drop leading minus.
> +                        * 2) Add leading minus.
> +                        * 3) Leave 0 as is.
> +                        */
> +                       if (orient[0] == '-')
> +                               str = devm_kstrdup(dev, orient + 1, GFP_KERNEL);

> +                       else if (orient[0] != '0' || orient[1] != '\0')
> +                               str = devm_kasprintf(dev, GFP_KERNEL, "-%s", orient);

I would go with the logic I suggested later on, i.e.

                       else if (orient[0] == '0' && orient[1] == '\0')
                               str = devm_kstrdup(dev, orient, GFP_KERNEL);

and below changed accordingly. It will clarify the "0" check.

> +                       else
> +                               str = devm_kstrdup(dev, orient, GFP_KERNEL);

> +

Redundant blank line.

> +                       if (!str)
>                                 return -ENOMEM;

-- 
With Best Regards,
Andy Shevchenko