linux-kernel - Re: [PATCH 0/2] vfs: ensure that dentries are revalidated on open (try #2)

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Date:	Wed, 18 Nov 2009 20:33:08 +0100
From:	Pavel Machek <pavel@....cz>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] vfs: ensure that dentries are revalidated on open
 (try #2)

Hi!

> > > Does it? Here's what I just did to check that:
> > 
> > Yes it does, see http://seclists.org/bugtraq/2009/Oct/179
...
> > /proc does not allow you to use /proc/XX/fd of unrelated users; it is
> > another mechanism disallowing access. (Plus, I did my experiments with
> > /proc/XX/fd, not /exe).

> Thanks for the info. Took me a while to get through it but I read most
> of the thread. I agree that it sounds like a very similar problem.
> 
> I'm beginning to wonder whether the right answer is to just make
> these /proc symlinks behave more like normal symlinks. Get rid of
> LAST_BIND and have follow_link turn the dentry into a path via
> d_path().

That would work for me.

> It's less efficient, but it means less special-casing in the path
> walking code. I don't see /proc symlinks as being so performance
> critical that we can't do it that way instead.

Current approach works with deleted files; without special-casing that
will stop. But I see it as a good thing: you should not have to chmod
000 before deleting a file.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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