linux-kernel - Re: [PATCH] firmware: dmi: Check DMI structure length

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Date:   Thu, 1 Jun 2017 16:40:19 +0200
From:   Jean Delvare <jdelvare@...e.de>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH] firmware: dmi: Check DMI structure length

Hi Andy,

Thanks for the review.

On Thu, 1 Jun 2017 16:16:05 +0300, Andy Shevchenko wrote:
> On Thu, Jun 1, 2017 at 4:08 PM, Jean Delvare <jdelvare@...e.de> wrote:
> > Before accessing DMI data to record it for later, we should ensure
> > that the DMI structures are large enough to contain the data in
> > question.  
> 
> > -       const u8 *d = (u8 *) dm + index;
> > +       const u8 *d;  
> 
> > +       d = (u8 *) dm + index;  
> 
> I think you may leave this as is and make it compiler's burden to optimize.

Is there any benefit except making the patch smaller?

> > -       const u8 *d = (u8 *) dm + index;
> > +       const u8 *d;  
> 
> > +       d = (u8 *) dm + index;  
> 
> Ditto.
> 
> > -       int i, count = *(u8 *)(dm + 1);
> > +       int i, count;  
> 
> > +       count = *(u8 *)(dm + 1);  
> 
> Ditto.

I would expect a static code analyzer to complain about at least the
last one. Dereferencing a pointer before checking its validity is bad.

I'm not a big fan of counting of compiler optimizations to make the
code right.

-- 
Jean Delvare
SUSE L3 Support