linux-kernel - Re: backlight: catch invalid input

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Message-ID: <20081122103717.GA8136@elf.ucw.cz>
Date:	Sat, 22 Nov 2008 11:37:17 +0100
From:	Pavel Machek <pavel@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	rpurdie@...ys.net, linux-kernel@...r.kernel.org
Subject: Re: backlight: catch invalid input

On Fri 2008-11-21 15:54:21, Andrew Morton wrote:
> On Fri, 21 Nov 2008 12:14:14 +0100
> Pavel Machek <pavel@...e.cz> wrote:
> 
> > 
> > Currently, echo > brightness turns brightness to zero due to
> > insufficient checking. Add a test to catch that.
> > 
> 
> OK.  And what happens if you do
> 
> 	echo wibble > brightness
> 
> ?

That's okay, that is catched by tests already existing in there. size
is the size we decoded, count is how many bytes user wrote. If (size
!= count), we return failure.

But there's an exception for whitespace, and missing check for nothing
at all being written.

> > diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
> > index fab0bc8..5c2e23d 100644
> > --- a/drivers/video/backlight/backlight.c
> > +++ b/drivers/video/backlight/backlight.c
> > @@ -86,6 +86,8 @@ static ssize_t backlight_store_power(str
> >  	int power = simple_strtoul(buf, &endp, 0);
> >  	size_t size = endp - buf;
> >  
> > +	if (!size)
> > +		return -EINVAL;
> >  	if (*endp && isspace(*endp))
> >  		size++;
> >  	if (size != count)
> 
> A better fix would be to use strict_strtoul() and check its return
> value.

Aha, here's the hint :-). Ok, will do.
									Pavel

-- 
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