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

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Message-ID: <20091206084633.GA2766@ucw.cz>
Date:	Sun, 6 Dec 2009 09:46:33 +0100
From:	Pavel Machek <pavel@....cz>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	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 2009-12-02 17:16:57, Miklos Szeredi wrote:
> v2->v3 slightly updated patch description
> 
> Thanks to Alan for the feedback.  The main points raised were I think:
> 
> 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.

Perhaps machine has /dev on separate filesystem, not writeable to
users?

Adding new security holes is bad...

> 3) There's an alleged security hole (commonly referred to as "Pavel's
> issue" :) with reopening for write (or truncating) a file desciptor
> through /proc/P/fd for a file descriptor opened for read-only.
> 
> This patch doens't change any of that except the file opened without
> any permission can also be re-opened with increased permissions, as
> long as i_mode allows.  I think this is an othogonal issue and so this
> patch doesn't deal with it.

You just made the hole way more common and easier to exploit.

> Comments?  Any chance of this being accepted into -mm?

With adding 2 new security problems?
									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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