linux-kernel - Re: [PATCH v3 10/12] ima: defer calling _

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Message-ID: <20120322150945.GW6589@ZenIV.linux.org.uk>
Date:	Thu, 22 Mar 2012 15:09:45 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
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, Mar 22, 2012 at 10:53:04AM -0400, Mimi Zohar wrote:
> > 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.

Don't do it, then?  If you _must_ write to xattr on final fput, I'd suggest
starting to figure out if xattr needs its protection to be ->i_mutex - it
might make sense to introduce a separate mutex for xattr crap.  Or not - I'm
not familiar enough with the guts of xattr handling in individual filesystems
to tell if that would work (e.g. if it would need unpleasant changes to
->setattr() instances)...
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