linux-kernel - Re: strict copy_from

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Message-ID: <4B43B2D7.6000208@zytor.com>
Date:	Tue, 05 Jan 2010 13:44:55 -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 01/05/2010 07:20 AM, Arnd Bergmann wrote:
> 
> You mean like this?
> 
> It adds some complexity and about 200 bytes of object code,
> I'm not sure it's worth it.
> 

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...

> --
> [UNTESTED PATCH] tun: avoid copy_from_user size warning
> 
> For 32 bit compat code, the tun driver only copies the
> fields it needs using a short length, which copy_from_user
> now warns about. Moving the copy operation outside of the
> main ioctl function lets us avoid the warning.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

	-hpa

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