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

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Message-ID: <CAKSJeFKR+jWYiMiexvqGyBQe-=hGmq0DO0TZK-EQszTwcbmG4A@mail.gmail.com>
Date:	Wed, 17 Jun 2015 13:45:27 +0200
From:	Morten Stevens <mstevens@...oraproject.org>
To:	Daniel Wagner <wagi@...om.org>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Prarit Bhargava <prarit@...hat.com>,
	Morten Stevens <mstevens@...oraproject.org>,
	Dave Chinner <david@...morbit.com>,
	Eric Paris <eparis@...hat.com>,
	Eric Sandeen <esandeen@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: mm: shmem_zero_setup skip security check and lockdep conflict
 with XFS

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.

Best regards,

Morten
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