linux-kernel - Re: strict copy_from

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Message-Id: <201001071502.29777.arnd@arndb.de>
Date:	Thu, 7 Jan 2010 15:02:29 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	"H. Peter Anvin" <hpa@...or.com>
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 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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