linux-kernel - Re: [PATCH] [RFC] fs: Possible filp

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Date:   Tue, 31 Jan 2017 13:58:14 +0100
From:   Christoph Hellwig <hch@....de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Marek Vasut <marex@...x.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        hch@....de, Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Joel Becker <jlbec@...lplan.org>
Subject: Re: [PATCH] [RFC] fs: Possible filp_open race experiment

On Tue, Jan 31, 2017 at 11:21:02AM +0100, Greg Kroah-Hartman wrote:
> 
> -next isn't Linus's tree, sometimes stuff sits in there for years :)
> 
> Anyway, if this is a configfs issue, Christoph and Joel can take a look
> at it.  Any reason you didn't cc: Joel as well (the MAINTAINERS file is
> your friend...)

It's really a mismatched assumption.  The configfs binary file
code just chunks updates up into a buffer, which only gets flushed
at ->release time.  If we'd move that to ->flush the issue Marek reports
would be fixed.

But I don't think we want that - triggering a filp_open from the update
of a _binary_ attribute for a start is wrong.  And second doing this
using ->fs of a random calling process is bound to cause problems.

I think he is using the wrong kind of interface for the job.