linux-kernel - Re: [PATCH v3] vfs: new O

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Date:	Wed, 02 Dec 2009 21:13:46 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	miklos@...redi.hu, akpm@...ux-foundation.org,
	viro@...IV.linux.org.uk, dhowells@...hat.com, hch@...radead.org,
	adilger@....com, mtk.manpages@...il.com,
	torvalds@...ux-foundation.org, drepper@...il.com,
	jamie@...reable.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] vfs: new O_NODE open flag

On Wed, 2 Dec 2009, Alan Cox wrote:
> > 1) There's a security hole with dynamicly allocated devices if
> > permissions on new device are difference than on old device.
> > 
> > The issue is valid, but also exists if hard links are created to
> > device nodes.  udev already defends against this by setting
> > permissions on device to zero before unlinking it.
> 
> udev defends against it with the specific knowledge that any existing
> open means the device is open and cannot be unloaded. The combination is
> required (and some other happenstance properties).

You're still missing the point.  O_NODE is like a hard link, except
the reference doesn't come from the filesystem but from a file
descriptor.  From udev's perspective there's no difference.

Miklos
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