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Message-ID: <1332427986.2218.53.camel@falcor>
Date: Thu, 22 Mar 2012 10:53:04 -0400
From: Mimi Zohar <zohar@...ux.vnet.ibm.com>
To: Al Viro <viro@...IV.linux.org.uk>
Cc: linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
David Safford <safford@...ux.vnet.ibm.com>,
Dmitry Kasatkin <dmitry.kasatkin@...el.com>,
Matt Helsley <matt.helsley@...il.com>,
Mimi Zohar <zohar@...ibm.com>
Subject: Re: [PATCH v3 10/12] ima: defer calling __fput()
On Thu, 2012-03-22 at 14:22 +0000, Al Viro wrote:
> On Wed, Mar 21, 2012 at 02:54:15PM -0400, Mimi Zohar wrote:
> > If a file is closed before it is munmapped, __fput() is called with
> > the mmap_sem taken. With IMA-appraisal enabled, this results in an
> > mmap_sem/i_mutex lockdep. ima_defer_fput() increments the f_count
> > to defer __fput() being called until after the mmap_sem is released.
>
> NAK. It's far too heavy-weight for what's a very common path. Worse,
> it causes different locking conditions on IMA and non-IMA kernels and makes
> bugs harder to spot. Rejected with extreme prejudice; please, fix your
> locking instead.
Al, thanks for replying! I realize you are very prejudiced against IMA,
but have you taken a look at IMA-appraisal? It probably would have been
better if we used another name in order to avoid this prejudice, but
unfortunately we didn't. :( IMA-appraisal is about enforcing file
integrity.
> BTW, you've missed several other places in mm/* doing fput(), so it wouldn't
> be enough to paper over your problem anyway.
>
> Final fput() *can* happen under mmap_sem. Period.
I think I got that loud and clear; otherwise we wouldn't have come up
with deferring the __fput(). We have a very real problem here - writing
extended attributes requires taking the i_mutex. I'm open to any
suggestions.
thanks,
Mimi
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