linux-kernel - Re: [PATCH] staging/fbtft: Remove all strcpy() uses

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Date:   Mon, 19 Jul 2021 09:53:29 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Len Baker <len.baker@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Phil Reid <preid@...ctromag.com.au>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "open list:FRAMEBUFFER LAYER" <linux-fbdev@...r.kernel.org>,
        linux-staging@...ts.linux.dev,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging/fbtft: Remove all strcpy() uses

On Sun, Jul 18, 2021 at 9:43 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Sun, Jul 18, 2021 at 4:43 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. 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@...ux-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