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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Sun, 8 Aug 2021 22:00:34 +0300
Message-ID: <CAHp75VfSX-7UqH9Lbr_GxQRY3dGjGo7H8++kBdrrSds1p6nB1Q@mail.gmail.com>
Subject: Re: [PATCH v2] drivers/iio: Remove all strcpy() uses in favor of strscpy()
To:     Jonathan Cameron <jic23@kernel.org>
Cc:     Len Baker <len.baker@gmx.com>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Kees Cook <keescook@chromium.org>,
        linux-hardening@vger.kernel.org,
        linux-iio <linux-iio@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Sun, Aug 8, 2021 at 7:25 PM Jonathan Cameron <jic23@kernel.org> wrote:
>
> On Sat,  7 Aug 2021 17:22:25 +0200
> Len Baker <len.baker@gmx.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. The safe replacement is strscpy().
> >
> > 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
> >
> > Signed-off-by: Len Baker <len.baker@gmx.com>
> Applied to the togreg branch of iio.git and pushed out as testing
> so 0-day can poke at it and see if we missed anything.

Isn't it too early? Or am I missing something (see below)?

...

> >                       /* use length + 2 for adding minus sign if needed */
> > -                     str = devm_kzalloc(regmap_get_device(st->map),
> > -                                        strlen(orient) + 2, GFP_KERNEL);
> > +                     n = strlen(orient) + 2;
> > +                     str = devm_kzalloc(regmap_get_device(st->map), n,
> > +                                        GFP_KERNEL);
> >                       if (str == NULL)
> >                               return -ENOMEM;
> >                       if (strcmp(orient, "0") == 0) {
> > -                             strcpy(str, orient);
> > +                             strscpy(str, orient, n);
> >                       } else if (orient[0] == '-') {
> > -                             strcpy(str, &orient[1]);
> > +                             strscpy(str, &orient[1], n);
> >                       } else {
> >                               str[0] = '-';
> > -                             strcpy(&str[1], orient);
> > +                             strscpy(&str[1], orient, n - 1);

Why n-1?

> >                       }

As far as I understood the logic, it  inverts the sign except the case
when it equals 0.

I have a question here, why can't we always use +/-?
Why can't 0 be prefixed with a sign?

If the above can be used, we may simplify this code.

Len, I think this task may be considered simple, but I recommend
thinking about each case and finding a way to simplify it more.

-- 
With Best Regards,
Andy Shevchenko