linux-kernel - Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

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Message-ID: <CANsGZ6aEKYgnGZyqO8VrpL8t=68Fwzt5WYbjtC7Nzq0uKPteUw@mail.gmail.com>
Date:	Thu, 18 Jun 2015 01:22:50 +0100
From:	Hugh Dickins <hughd@...gle.com>
To:	Morten Stevens <mstevens@...oraproject.org>
Cc:	Daniel Wagner <wagi@...om.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Prarit Bhargava <prarit@...hat.com>,
	Dave Chinner <david@...morbit.com>,
	Eric Paris <eparis@...hat.com>,
	Eric Sandeen <esandeen@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: mm: shmem_zero_setup skip security check and lockdep conflict
 with XFS

 Wed, Jun 17, 2015 at 12:45 PM, Morten Stevens
<mstevens@...oraproject.org> wrote:
> 2015-06-15 8:09 GMT+02:00 Daniel Wagner <wagi@...om.org>:
>> On 06/14/2015 06:48 PM, Hugh Dickins wrote:
>>> It appears that, at some point last year, XFS made directory handling
>>> changes which bring it into lockdep conflict with shmem_zero_setup():
>>> it is surprising that mmap() can clone an inode while holding mmap_sem,
>>> but that has been so for many years.
>>>
>>> Since those few lockdep traces that I've seen all implicated selinux,
>>> I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
>>> v3.13's commit c7277090927a ("security: shmem: implement kernel private
>>> shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
>>> the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
>>>
>>> This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
>>> (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
>>> which cloned inode in mmap(), but if so, I cannot locate them now.
>>>
>>> Reported-and-tested-by: Prarit Bhargava <prarit@...hat.com>
>>> Reported-by: Daniel Wagner <wagi@...om.org>
>>
>> Reported-and-tested-by: Daniel Wagner <wagi@...om.org>
>>
>> Sorry for the long delay. It took me a while to figure out my original
>> setup. I could verify that this patch made the lockdep message go away
>> on 4.0-rc6 and also on 4.1-rc8.
>
> Yes, it's also fixed for me after applying this patch to 4.1-rc8.

Thank you - Hugh

>
> Best regards,
>
> Morten
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