linux-kernel - Re: [PATCH] fb: sm501fb off-by-1 sysfs store

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Message-ID: <20070301091633.GA21140@fluff.org.uk>
Date:	Thu, 1 Mar 2007 09:16:33 +0000
From:	Ben Dooks <ben-linux@...ff.org>
To:	Paul Mundt <lethal@...ux-sh.org>, linux-kernel@...r.kernel.org,
	linux-fbdev-devel@...ts.sourceforge.net
Subject: Re: [PATCH] fb: sm501fb off-by-1 sysfs store

On Thu, Mar 01, 2007 at 05:24:56PM +0900, Paul Mundt wrote:
> Currently sm501fb_crtsrc_store() won't allow the routing to be changed
> via echos from userspace in to the sysfs file. The reason for this is
> that the strnicmp() for both heads uses a sizeof() for the string length,
> which ends up being strlen() + 1 (\0 in the normal case, but the echo
> gives a newline, which is where the issue occurs), this then causes a
> mismatch and subsequently bails with the -EINVAL.
> 
> In addition to this, the hardcoded lengths were then used for the store
> length that was returned, which ended up being erroneous and resulting in
> a write error. There's also no point in returning anything but the full
> length since it will -EINVAL out on a mismatch well before then anyways.
> 
> sizeof("string") is great for making sure you have space in your buffer,
> but rather less so for string comparisons :-)
> 
> Signed-off-by: Paul Mundt <lethal@...ux-sh.org>
Acked-by: Ben Dooks <ben-linux@...ff.org>

> --
> 
>  drivers/video/sm501fb.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/video/sm501fb.c b/drivers/video/sm501fb.c
> index 02b290c..72b5358 100644
> --- a/drivers/video/sm501fb.c
> +++ b/drivers/video/sm501fb.c
> @@ -1074,9 +1074,9 @@ static ssize_t sm501fb_crtsrc_store(struct device *dev,
>  	if (len < 1)
>  		return -EINVAL;
>  
> -	if (strnicmp(buf, "crt", sizeof("crt")) == 0)
> +	if (strnicmp(buf, "crt", 3) == 0)
>  		head = HEAD_CRT;
> -	else if (strnicmp(buf, "panel", sizeof("panel")) == 0)
> +	else if (strnicmp(buf, "panel", 5) == 0)
>  		head = HEAD_PANEL;
>  	else
>  		return -EINVAL;
> @@ -1098,7 +1098,7 @@ static ssize_t sm501fb_crtsrc_store(struct device *dev,
>  	writel(ctrl, info->regs + SM501_DC_CRT_CONTROL);
>  	sm501fb_sync_regs(info);
>  
> -	return (head == HEAD_CRT) ? 3 : 5;
> +	return len;
>  }
>  
>  /* Prepare the device_attr for registration with sysfs later */
> -
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-- 
Ben (ben@...ff.org, http://www.fluff.org/)

  'a smiley only costs 4 bytes'
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