Message-ID: <4B43B2D7.6000208@zytor.com>
Date: Tue, 05 Jan 2010 13:44:55 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Arnd Bergmann <arnd@arndb.de>
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
Subject: Re: strict copy_from_user checks issues?
References: <20100104154345.GA5671@osiris.boeblingen.de.ibm.com> <201001051445.26149.arnd@arndb.de> <20100105055224.39f9efff@infradead.org> <201001051620.38943.arnd@arndb.de>
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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@arndb.de>

	-hpa

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