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Message-ID: <CAL1RGDWM0C26YR+GGbguRQd0R3HoPJ5QVyEFkLGFfPqs6wb5Mg@mail.gmail.com>
Date: Fri, 17 Feb 2012 17:44:57 -0800
From: Roland Dreier <roland@...estorage.com>
To: Djalal Harouni <tixxdz@...ndz.org>
Cc: Vasiliy Kulikov <segoon@...nwall.com>, kernel-hardening@...ts.openwall.com,
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,
gregkh@...uxfoundation.org
Subject: Re: Re: Add overflow protection to kref
On Fri, Feb 17, 2012 at 3:39 PM, Djalal Harouni <tixxdz@...ndz.org> wrote:
>> 2) what to do with architectures-loosers?
> There is lib/atomic64.c but with a static hashed array of raw_spinlocks.
Even leaving aside performance impact of atomic64_t (and probably
in most cases the performance of kref is not important at all), it is
unfortunate to bloat the size from 4 bytes to 8 bytes.
It seems much better to have some out-of-line code for overflow
checking rather than increasing the size of every data structure
that embeds a kref.
Greg, I'm not sure why you're opposed to adding this checking...
it's pretty clear that buggy error paths that forget to do a put are
pretty common and will continue to be common in new code, and
making them harder to exploit seems pretty sane to me.
What's the downside?
- R.
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