linux-kernel - Re: [PATCH 5/9] staging: panel: check put

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Date:	Sat, 31 Jul 2010 10:39:51 +0200
From:	walter harms <wharms@....de>
To:	Willy Tarreau <w@....eu>
CC:	Kulikov Vasiliy <segooon@...il.com>,
	kernel-janitors@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Peter Huewe <peterhuewe@....de>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	Julia Lawall <julia@...u.dk>, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/9] staging: panel: check put_user() return value



Willy Tarreau schrieb:
> On Fri, Jul 30, 2010 at 03:08:42PM +0400, Kulikov Vasiliy wrote:
>> diff --git a/drivers/staging/panel/panel.c b/drivers/staging/panel/panel.c
>> index f58da32..57f4946 100644
>> --- a/drivers/staging/panel/panel.c
>> +++ b/drivers/staging/panel/panel.c
>> @@ -1589,25 +1589,30 @@ void lcd_init(void)
>>  static ssize_t keypad_read(struct file *file,
>>  			   char *buf, size_t count, loff_t *ppos)
>>  {
>> -
>> +	int buflen = keypad_buflen;
>>  	unsigned i = *ppos;
>>  	char *tmp = buf;
>> +	int start = keypad_start;
>>  
>> -	if (keypad_buflen == 0) {
>> +	if (buflen == 0) {
>>  		if (file->f_flags & O_NONBLOCK)
>>  			return -EAGAIN;
>>  
>>  		interruptible_sleep_on(&keypad_read_wait);
>>  		if (signal_pending(current))
>>  			return -EINTR;
>> +		buflen = keypad_buflen;
>>  	}
> 
> Not sure what the intent was here, I think you're re-adjusting
> the buffer's length in case something else was read. But then
> I don't understand why buflen it not simply assigned after the
> if() block.
> 
> The rest below looks fine otherwise.
> 
>>  
>> -	for (; count-- > 0 && (keypad_buflen > 0);
>> -	     ++i, ++tmp, --keypad_buflen) {
>> -		put_user(keypad_buffer[keypad_start], tmp);
>> -		keypad_start = (keypad_start + 1) % KEYPAD_BUFFER;
>> +	for (; count-- > 0 && (buflen > 0);
>> +	     ++i, ++tmp, --buflen) {
>> +		if (put_user(keypad_buffer[start], tmp))
>> +			return -EFAULT;
>> +		start = (start + 1) % KEYPAD_BUFFER;
>>  	}
>>  	*ppos = i;
>> +	keypad_buflen = buflen;
>> +	keypad_start = start;
>>  
>>  	return tmp - buf;
>>  }
> 
> 

IMHO opinion the for() construct breaks the rule of "no surprise please".
perhaps a while() would improve readability.

just my two cents,
re,
 wh




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