linux-kernel - Re: [PATCH 1/2] Introduce check_readable

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Message-ID: <87iqk3zhwl.wl%vmayatsk@redhat.com>
Date:	Thu, 14 May 2009 19:57:46 +0200
From:	Vitaly Mayatskikh <v.mayatskih@...il.com>
To:	Josef Bacik <josef@...hat.com>
Cc:	Vitaly Mayatskikh <v.mayatskih@...il.com>, sandeen@...hat.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] Introduce check_readable_bytes()

At Thu, 14 May 2009 13:40:09 -0400, Josef Bacik wrote:

> > +	volatile char c;
> > +	int ret = 0;
> > +	long page_begin = (unsigned long)uaddr & PAGE_MASK;
> > +	long page_end = ((unsigned long)uaddr + size) & PAGE_MASK;
> > +	long ptr = page_begin;
> > +
> 
> Firstly page_begin/page_end/ptr should all be unsigned long.  Secondly page_end
> should be uaddr+size-1.
> 
> > +	if (unlikely(size == 0))
> > +		goto out;
> > +
> > +	while (!ret && ptr <= page_end) {
> > +		ret = __get_user(c, (const char __user*)ptr);
> > +		if (!ret)
> > +			ptr += PAGE_SIZE;
> > +	}
> > +
> > +	if (likely(!ret))
> > +		ret = size;
> > +	else
> > +		ret = (ptr == page_begin) ?
> > +			-EFAULT : (const char __user *)ptr - uaddr;
> 
> This isn't quite right either, we do some pointer math, and return that and its
> casted as an int?  That seems like a bad idea in general.  Thanks,

Did you like the approach in general?

-- 
wbr, Vitaly
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