From: Arnd Bergmann <arnd@arndb.de>
To: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: strict copy_from_user checks issues?
Date: Thu, 7 Jan 2010 15:02:29 +0100
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Cc: Arjan van de Ven <arjan@infradead.org>,
       Heiko Carstens <heiko.carstens@de.ibm.com>, Ingo Molnar <mingo@elte.hu>,
       David Miller <davem@davemloft.net>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
References: <20100104154345.GA5671@osiris.boeblingen.de.ibm.com> <201001051620.38943.arnd@arndb.de> <4B43B2D7.6000208@zytor.com>
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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.

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.

	Arnd
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