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

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Message-ID: <Zc4YZo8Pt5qA9R38@smile.fi.intel.com>
Date: Thu, 15 Feb 2024 15:57:58 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
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

On Thu, Feb 15, 2024 at 01:33:29PM +0100, Geert Uytterhoeven wrote:
> 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).

I see the point, yes, we need an additional check.

-- 
With Best Regards,
Andy Shevchenko