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

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Message-ID: <20150422012633.GA2680@shlinux2>
Date:	Wed, 22 Apr 2015 09:26:35 +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 Tue, Apr 21, 2015 at 09:25:41PM +0200, Heinrich Schuchardt wrote:
> Hello Peter,
> 
> thanks for reviewing.
> 
> On 21.04.2015 03:32, Peter Chen wrote:
> > 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?
> 
> Otherwise we would have two lines with the term
> min_t(size_t, sizeof(buf) - 1, count).

Sorry, two lines of min_t(..)? Why I can't find it?


> 
> This would make the code harder to read.
> 
> >>  
> >> +	/* sscanf requires a zero terminated string */
> >> +	buf[count] = 0;
> >> +
> > 
> > I prefer using '\0'
> 
> If you confirm the rest of the patch is ok, I will send an updated patch.
> 
> Best regards
> 
> Heinrich
> 
> > 
> >>  	if (sscanf(buf, "%u", &mode) != 1)
> >>  		return -EINVAL;
> >>  
> 

-- 

Best Regards,
Peter Chen
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