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

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Message-ID: <5536A435.1030808@gmx.de>
Date:	Tue, 21 Apr 2015 21:25:41 +0200
From:	Heinrich Schuchardt <xypron.glpk@....de>
To:	Peter Chen <peter.chen@...escale.com>
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

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).

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;
>>  

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