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

From: Morten Stevens
Date: Wed Jun 17 2015 - 07:45:43 EST

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.

Best regards,

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