linux-kernel - Re: [PATCH 1/2] debugfs: prevent access to possibly dead file

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Date:	Mon, 30 Nov 2015 17:25:35 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Nicolai Stange <nicstange@...il.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Jonathan Corbet <corbet@....net>, Jan Kara <jack@...e.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] debugfs: prevent access to possibly dead
 file_operations at file open

On Tue, Dec 01, 2015 at 12:21:31AM +0100, Nicolai Stange wrote:
> Nothing prevents a dentry found by path lookup before a return of
> __debugfs_remove() to actually get opened after that return. Now, after
> the return of __debugfs_remove(), there are no guarantees whatsoever
> regarding the memory the corresponding inode's file_operations object
> had been kept in.
> 
> Since __debugfs_remove() is seldomly invoked, usually from module exit
> handlers only, the race is hard to trigger and the impact is very low.
> 
> A discussion of the problem outlined above as well as a suggested
> solution can be found in the (sub-)thread rooted at
> 
>   http://lkml.kernel.org/g/20130401203445.GA20862@ZenIV.linux.org.uk
>   ("Yet another pipe related oops.")
> 
> Basically, Greg KH suggests to introduce an intermediate fops and
> Al Viro points out that a pointer to the original ones may be stored in
> ->d_fsdata.

Nice work, thanks for doing this.  I'll review it in a week or so when
I've caught up on my huge pending patch queue...

greg k-h
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