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

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Date:   Sat, 24 Jul 2021 13:15:32 +0200
From:   Len Baker <len.baker@....com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Len Baker <len.baker@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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 Mon, Jul 19, 2021 at 09:53:29AM +0200, Geert Uytterhoeven wrote:
> 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.

Ok, understood. Thanks.

>
> > > 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".

Ok, I will work on it and I will send a v2 for review. Thanks for the
feedback.

>
> 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

Regards,
Len