linux-kernel - Re: strict copy_from

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Message-ID: <4B4674FF.5070700@zytor.com>
Date:	Thu, 07 Jan 2010 15:57:51 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Arjan van de Ven <arjan@...radead.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: strict copy_from_user checks issues?

On 01/07/2010 06:02 AM, Arnd Bergmann wrote:
> On Tuesday 05 January 2010, H. Peter Anvin wrote:
>> What's much worse is that it adds churn to an otherwise-tested code path.
>>
>> We almost need a copy_from/to_user_audited() to override the warning.
>> Not that errors can't creap back in...
>>
> 
> Maybe just splitting it up into access_ok() and __copy_from_user(),
> plus a comment is enough? That way we don't need to add another interface
> for the rare case.
> 

Adding a named interface makes it clear *what* you are doing and
*why*... just open-coding the implementation does neither.

> On a related topic, one interface that may actually be worth adding is
> a get_user/put_user variant that can operate on full data structures
> and return -EFAULT on failure rather than the number of remaining
> bytes that 99% of the code never need.

What is wrong with checking for zero?

	-hpa

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