linux-kernel - Re: [PATCH 1/1] drivers/usb/chipidea/debuc.c: avoid out of bound read

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Message-ID: <20150421013254.GA25710@shlinux2>
Date:	Tue, 21 Apr 2015 09:32:56 +0800
From:	Peter Chen <peter.chen@...escale.com>
To:	Heinrich Schuchardt <xypron.glpk@....de>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] drivers/usb/chipidea/debuc.c: avoid out of bound read

On Fri, Apr 17, 2015 at 08:04:13AM +0200, Heinrich Schuchardt wrote:
> A string written by the user may not be zero terminated.
> 
> sscanf may read memory beyond the buffer if no zero byte
> is found.
> 
> Signed-off-by: Heinrich Schuchardt <xypron.glpk@....de>
> ---
>  drivers/usb/chipidea/debug.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/chipidea/debug.c b/drivers/usb/chipidea/debug.c
> index dfb05ed..ef08af3 100644
> --- a/drivers/usb/chipidea/debug.c
> +++ b/drivers/usb/chipidea/debug.c
> @@ -88,9 +88,13 @@ static ssize_t ci_port_test_write(struct file *file, const char __user *ubuf,
>  	char buf[32];
>  	int ret;
>  
> -	if (copy_from_user(buf, ubuf, min_t(size_t, sizeof(buf) - 1, count)))
> +	count = min_t(size_t, sizeof(buf) - 1, count);
> +	if (copy_from_user(buf, ubuf, count))
>  		return -EFAULT;

Any reasons to change above?
>  
> +	/* sscanf requires a zero terminated string */
> +	buf[count] = 0;
> +

I prefer using '\0'

>  	if (sscanf(buf, "%u", &mode) != 1)
>  		return -EINVAL;
>  
> -- 
> 2.1.4
> 

-- 

Best Regards,
Peter Chen
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