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Date: Fri, 17 Feb 2012 23:37:19 +0400
From: Vasiliy Kulikov <segoon@...nwall.com>
To: kernel-hardening@...ts.openwall.com
Cc: Kees Cook <keescook@...omium.org>,
Ubuntu security discussion <ubuntu-hardened@...ts.ubuntu.com>,
linux-kernel@...r.kernel.org, David Windsor <dwindsor@...il.com>,
pageexec@...email.hu, spender@...ecurity.net
Subject: Re: Re: Add overflow protection to kref
On Fri, Feb 17, 2012 at 09:54 -0800, Greg KH wrote:
> I'm referring to the fact that the use of kref in this type of error or
> problem is rare.
>
> Yes, we have these types of problems at times, but a kref doesn't seem
> to be involved in them that I know of, so changing the kref code
> wouldn't help here from what I can tell.
Ehr, what's the difference between kref and "raw" atomic_t in a refcounting case?
There is _no_ difference in sense of overflows as a kref uses the same atomic_t.
I second David that we should use kref for overflow protection: we want to
hook an overflow case somehow in cases atomic_t is used as a refcounter. It is
_ideally_ handled by introducing atomic_t's subtype. And this subtype already
exists - it is called kref.
I expect all atomic_t refcounters users have
if (atomic_dec_and_test()) smth_put()
pattern, otherwise it is not a true refcounter :) It should be straightforward to
move to kref.
Moving to atomic64_t is attractive, but:
1) we still should find all atomic_t refcounters. Why not move to kref then?
2) what to do with architectures-loosers?
Thanks,
--
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
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