Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210718133920.15825-1-len.baker@gmx.com> <CAHp75VeEA0=KFsfdjCnBm-b9+F+NnFWJ38nkh+qtb85XdXVWog@mail.gmail.com>
In-Reply-To: <CAHp75VeEA0=KFsfdjCnBm-b9+F+NnFWJ38nkh+qtb85XdXVWog@mail.gmail.com>
From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Mon, 19 Jul 2021 09:53:29 +0200
Message-ID: <CAMuHMdXnhzumSrr=MAkv5nwY2o8xCa4s5zKa9meJTuo0r9yABw@mail.gmail.com>
Subject: Re: [PATCH] staging/fbtft: Remove all strcpy() uses
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Len Baker <len.baker@gmx.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Phil Reid <preid@electromag.com.au>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        "open list:FRAMEBUFFER LAYER" <linux-fbdev@vger.kernel.org>,
        linux-staging@lists.linux.dev,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Sun, Jul 18, 2021 at 9:43 PM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
> On Sun, Jul 18, 2021 at 4:43 PM 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() but in
> > this case it is simpler to add NULL to the first position since we want

"NULL" is a pointer value, "NUL" is the character with value zero.

> > to empty the string.
>
> > This is a previous step in the path to remove the strcpy() function.
>
> Any document behind this (something to read on the site(s) more or
> less affiliated with what is going to happen in the kernel) to read
> background?
>
> ...
>
> >                 case -1:
> >                         i++;
> >                         /* make debug message */
> > -                       strcpy(msg, "");

While this strcpy() is provably safe at compile-time, and will probably
be replaced by an assignment to zero by the compiler...

> > +                       msg[0] = 0;
>
> Strictly speaking it should be '\0'.
>
> >                         j = i + 1;
> >                         while (par->init_sequence[j] >= 0) {
> >                                 sprintf(str, "0x%02X ", par->init_sequence[j]);

... the real danger is the

        strcat(msg, str);

on the next line.
Fortunately this whole debug printing block (including the strcpy)
can (and should) be rewritten to just use "%*ph".

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds