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

From: Hugh Dickins
Date: Wed Jun 17 2015 - 20:23:18 EST

Wed, Jun 17, 2015 at 12:45 PM, Morten Stevens
<mstevens@xxxxxxxxxxxxxxxxx> wrote:
> 2015-06-15 8:09 GMT+02:00 Daniel Wagner <wagi@xxxxxxxxx>:
>> 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@xxxxxxxxxx>
>>> Reported-by: Daniel Wagner <wagi@xxxxxxxxx>
>> Reported-and-tested-by: Daniel Wagner <wagi@xxxxxxxxx>
>> 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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