linux-kernel - Re: [KVM PATCH v3 2/2] kvm: add support for irqfd via eventfd-notification interface

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Message-ID: <alpine.DEB.1.10.0905031103290.7899@makko.or.mcafeemobile.com>
Date:	Sun, 3 May 2009 11:07:26 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Al Viro <viro@...IV.linux.org.uk>
cc:	Gregory Haskins <ghaskins@...ell.com>, kvm@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	avi@...hat.com
Subject: Re: [KVM PATCH v3 2/2] kvm: add support for irqfd via eventfd-notification
 interface

On Sun, 3 May 2009, Al Viro wrote:

> On Mon, Apr 27, 2009 at 02:33:34PM -0400, Gregory Haskins wrote:
> > +	/* We re-use eventfd for irqfd */
> > +	fd = sys_eventfd2(0, 0);
> > +	if (fd < 0) {
> > +		ret = fd;
> > +		goto fail;
> > +	}
> > +
> > +	/* We maintain a reference to eventfd for the irqfd lifetime */
> > +	file = eventfd_fget(fd);
> > +	if (IS_ERR(file)) {
> > +		ret = PTR_ERR(file);
> > +		goto fail;
> > +	}
> > +
> > +	irqfd->file = file;
> 
> This is just plain wrong.  You have no promise whatsoever that caller of
> that sucker won't race with e.g. dup2().  IOW, you can't assume that
> file will be of the expected kind.

The eventfd_fget() checks for the file_operations pointer, before 
returning the file*, and fails if the fd in not an eventfd. Or you have 
other concerns?



- Davide


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