linux-kernel - Re: [PATCH v2 10/15] auxdisplay: linedisp: Provide a small buffer in the struct linedisp

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Message-ID: <CAMuHMdUR8i_08bz_B6HTzD4yx4URaC5aGG6byYNbmLmM0Gb4=w@mail.gmail.com>
Date: Thu, 15 Feb 2024 13:33:29 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Robin van der Gracht <robin@...tonic.nl>, Paul Burton <paulburton@...nel.org>
Subject: Re: [PATCH v2 10/15] auxdisplay: linedisp: Provide a small buffer in
 the struct linedisp

Hi Andy,

On Thu, Feb 15, 2024 at 1:19 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
> On Thu, Feb 15, 2024 at 02:17:00PM +0200, Andy Shevchenko wrote:
> > On Thu, Feb 15, 2024 at 11:40:44AM +0100, Geert Uytterhoeven wrote:
> > > On Mon, Feb 12, 2024 at 6:04 PM Andy Shevchenko
> > > <andriy.shevchenko@...ux.intel.com> wrote:
> > > > +       linedisp->buf = buf ? buf : linedisp->curr;
> > > > +       linedisp->num_chars = buf ? num_chars : min(num_chars, LINEDISP_DEFAULT_BUF_SZ);
> > >
> > > I think it would be safer to return an error if buf == NULL and
> > > num_chars < LINEDISP_DEFAULT_BUF_SZ.
> >
> > I think you meant >= ?

Oops, yes/

> >
> > > Else a careless driver that doesn't check linedisp->num_chars might
> > > overflow the buffer.
> >
> > Okay, check has been added.
>
> Hold on, but I have min() being called, isn't it enough?

Yes you have.

A careless driver might not use linedisp->num_chars later, but instead
just hardcode e.g. memcpy(linedisp->buf, source, LARGE_BUF_SIZE).

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68korg

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