linux-kernel - Re: [PATCH 2/2] Perform check in iov_iter_fault_in_readable() by check_readable

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Message-ID: <20090515143726.GE8235@shareable.org>
Date:	Fri, 15 May 2009 15:37:27 +0100
From:	Jamie Lokier <jamie@...reable.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Vitaly Mayatskikh <v.mayatskih@...il.com>,
	Josef Bacik <josef@...hat.com>, sandeen@...hat.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] Perform check in iov_iter_fault_in_readable() by check_readable_bytes()

Andi Kleen wrote:
> > It would be quite nice if it were safe to call read(), get EFAULT
> 
> Even with that patch it is not safe, not even for write, because
> it's racy.

That's not necessarily a problem for the applications I described,
because they can be made to only increase access in parallel with
access; decreasing access can be synchronised over the whole program.

But I agree with you, as no application should depend on such subtle
details, which would probably be broken again in a future kernel anyway.

-- Jamie
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