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Message-ID: <CALLzPKa8zz9g_YrRzgJty2BRZe=9_Gt5cH+cXAzjRy-B8TaimA@mail.gmail.com>
Date: Thu, 22 Mar 2012 16:58:43 +0200
From: "Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>
To: Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc: Al Viro <viro@...iv.linux.org.uk>,
linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
David Safford <safford@...ux.vnet.ibm.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 4:53 PM, Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
> 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.
>>
In current solution, deferred call can be added directly to __fput and checking
if mmap_sem is locked.
>> 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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