From: Vasiliy Kulikov <segoon@openwall.com>
To: kernel-hardening@lists.openwall.com
Cc: Kees Cook <keescook@chromium.org>,
Ubuntu security discussion <ubuntu-hardened@lists.ubuntu.com>,
linux-kernel@vger.kernel.org, David Windsor <dwindsor@gmail.com>,
Greg KH <gregkh@linuxfoundation.org>,
pageexec@freemail.hu, spender@grsecurity.net
Subject: Re: [kernel-hardening] Re: Add overflow protection to kref
Date: Fri, 17 Feb 2012 11:59:45 +0400 [thread overview]
Message-ID: <20120217075945.GA2831@albatros> (raw)
In-Reply-To: <20120217002405.GB7746@kroah.com>
Hi,
> And in all that time, I've never seen an instance where you can overflow
> the reference count,
Do you mean that the overflow is theoretically impossible or that this
type of programmer error is rare?
If the former, it is only 2**32 incs - if you can find open() implementation
with a missing atomic_dec() in error path and you can call open() faster than
10000 times per second, you can overflow the counter in ~4 days.
If the latter, it is just a question of finding missing put() in some triggerable
error path. Kees has already posted a link to a bug with a missing fput().
BTW, moving from atomic_t to 64 bit refcounter would kill the possibility of
overflow. Unfortunately, AFAIU, 64 bit operations are not atomic on some 64 bit
archs.
Thanks,
--
Vasiliy
next prev parent reply other threads:[~2012-02-17 7:59 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-16 14:02 [kernel-hardening] Add overflow protection to kref David Windsor
2012-02-16 20:45 ` [kernel-hardening] " Kees Cook
2012-02-17 0:24 ` Greg Kroah-Hartman
2012-02-17 1:06 ` Kees Cook
2012-02-17 1:40 ` Greg KH
2012-02-17 2:11 ` [kernel-hardening] Re: [ubuntu-hardened] " Kees Cook
2012-02-17 2:48 ` David Windsor
2012-02-17 3:32 ` Greg KH
2012-02-17 6:33 ` Alexey Dobriyan
2012-02-17 13:23 ` [kernel-hardening] " pageexec
2012-02-17 7:59 ` Vasiliy Kulikov [this message]
2012-02-17 17:53 ` Greg KH
2012-02-17 17:54 ` Greg KH
2012-02-17 19:37 ` Vasiliy Kulikov
2012-02-17 23:39 ` Djalal Harouni
2012-02-18 1:44 ` Roland Dreier
2012-02-18 16:15 ` David Windsor
2012-02-18 16:35 ` Vasiliy Kulikov
2012-02-18 16:18 ` Greg KH
2012-02-24 17:58 ` David Windsor
2012-02-24 18:37 ` Greg KH
2012-02-24 18:52 ` Kees Cook
2012-02-24 19:05 ` Nick Bowler
2012-02-24 19:13 ` Vasiliy Kulikov
2012-02-24 19:35 ` Nick Bowler
2012-02-24 21:59 ` PaX Team
2012-02-24 18:58 ` Vasiliy Kulikov
2012-02-24 19:41 ` Greg KH
2012-02-24 20:04 ` Kees Cook
2012-02-24 19:04 ` David Windsor
2012-02-24 22:14 ` PaX Team
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