linux-kernel - Re: [PATCH] proc: revalidate dentry returned by proc_pid_follow

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Message-ID: <20091106203601.GD27751@shareable.org>
Date:	Fri, 6 Nov 2009 20:36:01 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-nfs@...r.kernel.org, adobriyan@...il.com,
	viro@...IV.linux.org.uk
Subject: Re: [PATCH] proc: revalidate dentry returned by proc_pid_follow_link

Jeff Layton wrote:
> The problem here is that this makes that code shortcut any lookup or
> revalidation of the dentry. In general, this isn't a problem -- in most
> cases the dentry is known to be good. It is a problem however for NFSv4.
> If this symlink is followed on an open operation no actual open call
> occurs and the open state isn't properly established. This causes
> problems when we later try to use this file descriptor for actual
> operations.

As NFS uses open() as a kind of fcntl-lock barrier, I can see it's
important to do _something_ on new opens, rather than just cloning
most of the file descriptor.

> This patch takes a minimalist approach to fixing this by making the
> /proc/pid follow_link routine revalidate the dentry before returning it.

What happens if the file descriptor you are re-opening is for a file
which has been deleted.  Does it still have a revalidatable dentry?

-- Jamie
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