linux-kernel - Re: [kernel-hardening] Re: Add overflow protection to kref

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Date:	Fri, 24 Feb 2012 23:59:47 +0200
From:	"PaX Team" <pageexec@...email.hu>
To:	Nick Bowler <nbowler@...iptictech.com>,
	Vasiliy Kulikov <segoon@...nwall.com>
CC:	Kees Cook <keescook@...omium.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	David Windsor <dwindsor@...il.com>,
	Roland Dreier <roland@...estorage.com>,
	Djalal Harouni <tixxdz@...ndz.org>,
	kernel-hardening@...ts.openwall.com,
	Ubuntu security discussion <ubuntu-hardened@...ts.ubuntu.com>,
	linux-kernel@...r.kernel.org, spender@...ecurity.net
Subject: Re: [kernel-hardening] Re: Add overflow protection to kref

On 24 Feb 2012 at 23:13, Vasiliy Kulikov wrote:

> > But in this case, the principle does not apply because we can recover.
> > The reason we cannot recover from the stack protector case is because
> > the stack protector is reacting after the fact, which is not the case
> > here.  Simply peg the reference count at the maximum value, neither
> > incrementing it nor decrementing it further.
> 
> ...and simply loose one reference, which leads to use-after-free.

saturating the refcount keeps the protected object allocated, so it is
a memory leak, but it is not a use-after-free.

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